Merge remote-tracking branch 'origin/master' into nixbuildaddprintstorepaths

doc/manual/src/release-notes/rl-next.md

@@ -3,5 +3,9 @@
 * `nix repl` has a new build-'n-link (`:bl`) command that builds a derivation
   while creating GC root symlinks.
 
+* The path produced by `builtins.toFile` is now allowed to be imported or read
+  even with restricted evaluation. Note that this will not work with a
+  read-only store.
+
 * `nix build` has a new `--print-out-paths` flag to print the resulting output paths.
   This matches the default behaviour of `nix-build`.

docker.nix

@@ -22,6 +22,7 @@ let
     findutils
     iana-etc
     git
+    openssh
   ];
 
   users = {

src/libcmd/command.cc

@@ -197,17 +197,17 @@ void StorePathCommand::run(ref<Store> store, std::vector<StorePath> && storePath
     run(store, *storePaths.begin());
 }
 
-Strings editorFor(const Pos & pos)
+Strings editorFor(const Path & file, uint32_t line)
 {
     auto editor = getEnv("EDITOR").value_or("cat");
     auto args = tokenizeString<Strings>(editor);
-    if (pos.line > 0 && (
+    if (line > 0 && (
         editor.find("emacs") != std::string::npos ||
         editor.find("nano") != std::string::npos ||
         editor.find("vim") != std::string::npos ||
         editor.find("kak") != std::string::npos))
-        args.push_back(fmt("+%d", pos.line));
+        args.push_back(fmt("+%d", line));
-    args.push_back(pos.file);
+    args.push_back(file);
     return args;
 }
 

src/libcmd/command.hh

@@ -219,7 +219,7 @@ static RegisterCommand registerCommand2(std::vector<std::string> && name)
 
 /* Helper function to generate args that invoke $EDITOR on
    filename:lineno. */
-Strings editorFor(const Pos & pos);
+Strings editorFor(const Path & file, uint32_t line);
 
 struct MixProfile : virtual StoreCommand
 {

src/libcmd/installables.cc

@@ -235,7 +235,7 @@ void SourceExprCommand::completeInstallable(std::string_view prefix)
 
         if (v2.type() == nAttrs) {
             for (auto & i : *v2.attrs) {
-                std::string name = i.name;
+                std::string name = state->symbols[i.name];
                 if (name.find(searchWord) == 0) {
                     if (prefix_ == "")
                         completions->add(name);
@@ -473,7 +473,7 @@ struct InstallableAttrPath : InstallableValue
 
     std::string what() const override { return attrPath; }
 
-    std::pair<Value *, Pos> toValue(EvalState & state) override
+    std::pair<Value *, PosIdx> toValue(EvalState & state) override
     {
         auto [vRes, pos] = findAlongAttrPath(state, attrPath, *cmd.getAutoArgs(state), **v);
         state.forceValue(*vRes, pos);
@@ -600,7 +600,7 @@ std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableF
 
     auto drvInfo = DerivationInfo {
         std::move(drvPath),
-        attr->getAttr(state->sOutputName)->getString()
+        attr->getAttr("outputName")->getString()
     };
 
     return {attrPath, getLockedFlake()->flake.lockedRef, std::move(drvInfo)};
@@ -613,7 +613,7 @@ std::vector<InstallableValue::DerivationInfo> InstallableFlake::toDerivations()
     return res;
 }
 
-std::pair<Value *, Pos> InstallableFlake::toValue(EvalState & state)
+std::pair<Value *, PosIdx> InstallableFlake::toValue(EvalState & state)
 {
     return {&getCursor(state)->forceValue(), noPos};
 }
@@ -831,8 +831,8 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> Installable::bui
                                 auto realisation = store->queryRealisation(outputId);
                                 if (!realisation)
                                     throw Error(
-                                        "cannot operate on an output of unbuilt "
+                                        "cannot operate on an output of the "
-                                        "content-addressed derivation '%s'",
+                                        "unbuilt derivation '%s'",
                                         outputId.to_string());
                                 outputs.insert_or_assign(output, realisation->outPath);
                             } else {

src/libcmd/installables.hh

@@ -68,7 +68,7 @@ struct Installable
 
     UnresolvedApp toApp(EvalState & state);
 
-    virtual std::pair<Value *, Pos> toValue(EvalState & state)
+    virtual std::pair<Value *, PosIdx> toValue(EvalState & state)
     {
         throw Error("argument '%s' cannot be evaluated", what());
     }
@@ -178,7 +178,7 @@ struct InstallableFlake : InstallableValue
 
     std::vector<DerivationInfo> toDerivations() override;
 
-    std::pair<Value *, Pos> toValue(EvalState & state) override;
+    std::pair<Value *, PosIdx> toValue(EvalState & state) override;
 
     /* Get a cursor to every attrpath in getActualAttrPaths() that
        exists. */

src/libexpr/attr-path.cc

@@ -36,18 +36,18 @@ std::vector<Symbol> parseAttrPath(EvalState & state, std::string_view s)
 {
     std::vector<Symbol> res;
     for (auto & a : parseAttrPath(s))
-        res.push_back(state.symbols.create(a));
+        res.emplace_back(a);
     return res;
 }
 
 
-std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const std::string & attrPath,
+std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::string & attrPath,
     Bindings & autoArgs, Value & vIn)
 {
     Strings tokens = parseAttrPath(attrPath);
 
     Value * v = &vIn;
-    Pos pos = noPos;
+    PosIdx pos = noPos;
 
     for (auto & attr : tokens) {
 
@@ -77,13 +77,13 @@ std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const std::string &
             if (a == v->attrs->end()) {
                 std::set<std::string> attrNames;
                 for (auto & attr : *v->attrs)
-                    attrNames.insert(attr.name);
+                    attrNames.insert(state.symbols[attr.name]);
 
                 auto suggestions = Suggestions::bestMatches(attrNames, attr);
                 throw AttrPathNotFound(suggestions, "attribute '%1%' in selection path '%2%' not found", attr, attrPath);
             }
             v = &*a->value;
-            pos = *a->pos;
+            pos = a->pos;
         }
 
         else {
@@ -106,7 +106,7 @@ std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const std::string &
 }
 
 
-Pos findPackageFilename(EvalState & state, Value & v, std::string what)
+std::pair<std::string, uint32_t> findPackageFilename(EvalState & state, Value & v, std::string what)
 {
     Value * v2;
     try {
@@ -132,9 +132,7 @@ Pos findPackageFilename(EvalState & state, Value & v, std::string what)
         throw ParseError("cannot parse line number '%s'", pos);
     }
 
-    Symbol file = state.symbols.create(filename);
+    return { std::move(filename), lineno };
-
-    return { foFile, file, lineno, 0 };
 }
 
 

src/libexpr/attr-path.hh

@@ -10,14 +10,14 @@ namespace nix {
 MakeError(AttrPathNotFound, Error);
 MakeError(NoPositionInfo, Error);
 
-std::pair<Value *, Pos> findAlongAttrPath(
+std::pair<Value *, PosIdx> findAlongAttrPath(
     EvalState & state,
     const std::string & attrPath,
     Bindings & autoArgs,
     Value & vIn);
 
 /* Heuristic to find the filename and lineno or a nix value. */
-Pos findPackageFilename(EvalState & state, Value & v, std::string what);
+std::pair<std::string, uint32_t> findPackageFilename(EvalState & state, Value & v, std::string what);
 
 std::vector<Symbol> parseAttrPath(EvalState & state, std::string_view s);
 

src/libexpr/attr-set.cc

@@ -26,7 +26,7 @@ Bindings * EvalState::allocBindings(size_t capacity)
 /* Create a new attribute named 'name' on an existing attribute set stored
    in 'vAttrs' and return the newly allocated Value which is associated with
    this attribute. */
-Value * EvalState::allocAttr(Value & vAttrs, const Symbol & name)
+Value * EvalState::allocAttr(Value & vAttrs, const SymbolIdx & name)
 {
     Value * v = allocValue();
     vAttrs.attrs->push_back(Attr(name, v));
@@ -40,7 +40,7 @@ Value * EvalState::allocAttr(Value & vAttrs, std::string_view name)
 }
 
 
-Value & BindingsBuilder::alloc(const Symbol & name, ptr<Pos> pos)
+Value & BindingsBuilder::alloc(const SymbolIdx & name, PosIdx pos)
 {
     auto value = state.allocValue();
     bindings->push_back(Attr(name, value, pos));
@@ -48,7 +48,7 @@ Value & BindingsBuilder::alloc(const Symbol & name, ptr<Pos> pos)
 }
 
 
-Value & BindingsBuilder::alloc(std::string_view name, ptr<Pos> pos)
+Value & BindingsBuilder::alloc(std::string_view name, PosIdx pos)
 {
     return alloc(state.symbols.create(name), pos);
 }

src/libexpr/attr-set.hh

@@ -15,18 +15,27 @@ struct Value;
 /* Map one attribute name to its value. */
 struct Attr
 {
-    Symbol name;
+    /* the placement of `name` and `pos` in this struct is important.
+       both of them are uint32 wrappers, they are next to each other
+       to make sure that Attr has no padding on 64 bit machines. that
+       way we keep Attr size at two words with no wasted space. */
+    SymbolIdx name;
+    PosIdx pos;
     Value * value;
-    ptr<Pos> pos;
+    Attr(SymbolIdx name, Value * value, PosIdx pos = noPos)
-    Attr(Symbol name, Value * value, ptr<Pos> pos = ptr(&noPos))
+        : name(name), pos(pos), value(value) { };
-        : name(name), value(value), pos(pos) { };
+    Attr() { };
-    Attr() : pos(&noPos) { };
     bool operator < (const Attr & a) const
     {
         return name < a.name;
     }
 };
 
+static_assert(sizeof(Attr) == 2 * sizeof(uint32_t) + sizeof(Value *),
+    "performance of the evaluator is highly sensitive to the size of Attr. "
+    "avoid introducing any padding into Attr if at all possible, and do not "
+    "introduce new fields that need not be present for almost every instance.");
+
 /* Bindings contains all the attributes of an attribute set. It is defined
    by its size and its capacity, the capacity being the number of Attr
    elements allocated after this structure, while the size corresponds to
@@ -35,13 +44,13 @@ class Bindings
 {
 public:
     typedef uint32_t size_t;
-    ptr<Pos> pos;
+    PosIdx pos;
 
 private:
     size_t size_, capacity_;
     Attr attrs[0];
 
-    Bindings(size_t capacity) : pos(&noPos), size_(0), capacity_(capacity) { }
+    Bindings(size_t capacity) : size_(0), capacity_(capacity) { }
     Bindings(const Bindings & bindings) = delete;
 
 public:
@@ -57,7 +66,7 @@ public:
         attrs[size_++] = attr;
     }
 
-    iterator find(const Symbol & name)
+    iterator find(const SymbolIdx & name)
     {
         Attr key(name, 0);
         iterator i = std::lower_bound(begin(), end(), key);
@@ -65,7 +74,7 @@ public:
         return end();
     }
 
-    Attr * get(const Symbol & name)
+    Attr * get(const SymbolIdx & name)
     {
         Attr key(name, 0);
         iterator i = std::lower_bound(begin(), end(), key);
@@ -73,18 +82,6 @@ public:
         return nullptr;
     }
 
-    Attr & need(const Symbol & name, const Pos & pos = noPos)
-    {
-        auto a = get(name);
-        if (!a)
-            throw Error({
-                .msg = hintfmt("attribute '%s' missing", name),
-                .errPos = pos
-            });
-
-        return *a;
-    }
-
     iterator begin() { return &attrs[0]; }
     iterator end() { return &attrs[size_]; }
 
@@ -98,14 +95,15 @@ public:
     size_t capacity() { return capacity_; }
 
     /* Returns the attributes in lexicographically sorted order. */
-    std::vector<const Attr *> lexicographicOrder() const
+    std::vector<const Attr *> lexicographicOrder(const SymbolTable & symbols) const
     {
         std::vector<const Attr *> res;
         res.reserve(size_);
         for (size_t n = 0; n < size_; n++)
             res.emplace_back(&attrs[n]);
-        std::sort(res.begin(), res.end(), [](const Attr * a, const Attr * b) {
+        std::sort(res.begin(), res.end(), [&](const Attr * a, const Attr * b) {
-            return (const std::string &) a->name < (const std::string &) b->name;
+            std::string_view sa = symbols[a->name], sb = symbols[b->name];
+            return sa < sb;
         });
         return res;
     }
@@ -130,7 +128,7 @@ public:
         : bindings(bindings), state(state)
     { }
 
-    void insert(Symbol name, Value * value, ptr<Pos> pos = ptr(&noPos))
+    void insert(SymbolIdx name, Value * value, PosIdx pos = noPos)
     {
         insert(Attr(name, value, pos));
     }
@@ -145,9 +143,9 @@ public:
         bindings->push_back(attr);
     }
 
-    Value & alloc(const Symbol & name, ptr<Pos> pos = ptr(&noPos));
+    Value & alloc(const SymbolIdx & name, PosIdx pos = noPos);
 
-    Value & alloc(std::string_view name, ptr<Pos> pos = ptr(&noPos));
+    Value & alloc(std::string_view name, PosIdx pos = noPos);
 
     Bindings * finish()
     {

src/libexpr/eval-cache.cc

@@ -253,7 +253,7 @@ struct AttrDb
                 std::vector<Symbol> attrs;
                 auto queryAttributes(state->queryAttributes.use()(rowId));
                 while (queryAttributes.next())
-                    attrs.push_back(symbols.create(queryAttributes.getStr(0)));
+                    attrs.emplace_back(queryAttributes.getStr(0));
                 return {{rowId, attrs}};
             }
             case AttrType::String: {
@@ -325,7 +325,7 @@ AttrCursor::AttrCursor(
 AttrKey AttrCursor::getKey()
 {
     if (!parent)
-        return {0, root->state.sEpsilon};
+        return {0, {""}};
     if (!parent->first->cachedValue) {
         parent->first->cachedValue = root->db->getAttr(
             parent->first->getKey(), root->state.symbols);
@@ -340,7 +340,7 @@ Value & AttrCursor::getValue()
         if (parent) {
             auto & vParent = parent->first->getValue();
             root->state.forceAttrs(vParent, noPos);
-            auto attr = vParent.attrs->get(parent->second);
+            auto attr = vParent.attrs->get(root->state.symbols.create(parent->second));
             if (!attr)
                 throw Error("attribute '%s' is unexpectedly missing", getAttrPathStr());
             _value = allocRootValue(attr->value);
@@ -419,7 +419,7 @@ Suggestions AttrCursor::getSuggestionsForAttr(Symbol name)
     return Suggestions::bestMatches(strAttrNames, name);
 }
 
-std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErrors)
+std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(std::string_view name, bool forceErrors)
 {
     if (root->db) {
         if (!cachedValue)
@@ -461,10 +461,10 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
 
     for (auto & attr : *v.attrs) {
         if (root->db)
-            root->db->setPlaceholder({cachedValue->first, attr.name});
+            root->db->setPlaceholder({cachedValue->first, root->state.symbols[attr.name]});
     }
 
-    auto attr = v.attrs->get(name);
+    auto attr = v.attrs->get(root->state.symbols.create(name));
 
     if (!attr) {
         if (root->db) {
@@ -486,12 +486,7 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
         root, std::make_pair(shared_from_this(), name), attr->value, std::move(cachedValue2));
 }
 
-std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(std::string_view name)
+ref<AttrCursor> AttrCursor::getAttr(std::string_view name, bool forceErrors)
-{
-    return maybeGetAttr(root->state.symbols.create(name));
-}
-
-ref<AttrCursor> AttrCursor::getAttr(Symbol name, bool forceErrors)
 {
     auto p = maybeGetAttr(name, forceErrors);
     if (!p)
@@ -499,11 +494,6 @@ ref<AttrCursor> AttrCursor::getAttr(Symbol name, bool forceErrors)
     return ref(p);
 }
 
-ref<AttrCursor> AttrCursor::getAttr(std::string_view name)
-{
-    return getAttr(root->state.symbols.create(name));
-}
-
 OrSuggestions<ref<AttrCursor>> AttrCursor::findAlongAttrPath(const std::vector<Symbol> & attrPath, bool force)
 {
     auto res = shared_from_this();
@@ -616,7 +606,7 @@ std::vector<Symbol> AttrCursor::getAttrs()
 
     std::vector<Symbol> attrs;
     for (auto & attr : *getValue().attrs)
-        attrs.push_back(attr.name);
+        attrs.push_back(root->state.symbols[attr.name]);
     std::sort(attrs.begin(), attrs.end(), [](const Symbol & a, const Symbol & b) {
         return (const std::string &) a < (const std::string &) b;
     });
@@ -635,7 +625,7 @@ bool AttrCursor::isDerivation()
 
 StorePath AttrCursor::forceDerivation()
 {
-    auto aDrvPath = getAttr(root->state.sDrvPath, true);
+    auto aDrvPath = getAttr("drvPath", true);
     auto drvPath = root->state.store->parseStorePath(aDrvPath->getString());
     if (!root->state.store->isValidPath(drvPath) && !settings.readOnlyMode) {
         /* The eval cache contains 'drvPath', but the actual path has

src/libexpr/eval-cache.hh

@@ -96,13 +96,9 @@ public:
 
     Suggestions getSuggestionsForAttr(Symbol name);
 
-    std::shared_ptr<AttrCursor> maybeGetAttr(Symbol name, bool forceErrors = false);
+    std::shared_ptr<AttrCursor> maybeGetAttr(std::string_view name, bool forceErrors = false);
 
-    std::shared_ptr<AttrCursor> maybeGetAttr(std::string_view name);
+    ref<AttrCursor> getAttr(std::string_view name, bool forceErrors = false);
-
-    ref<AttrCursor> getAttr(Symbol name, bool forceErrors = false);
-
-    ref<AttrCursor> getAttr(std::string_view name);
 
     /* Get an attribute along a chain of attrsets. Note that this does
        not auto-call functors or functions. */

src/libexpr/eval-inline.hh

@@ -2,27 +2,8 @@
 
 #include "eval.hh"
 
-#define LocalNoInline(f) static f __attribute__((noinline)); f
-#define LocalNoInlineNoReturn(f) static f __attribute__((noinline, noreturn)); f
-
 namespace nix {
 
-LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s))
-{
-    throw EvalError({
-        .msg = hintfmt(s),
-        .errPos = pos
-    });
-}
-
-LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const char * s, const Value & v))
-{
-    throw TypeError({
-        .msg = hintfmt(s, showType(v)),
-        .errPos = pos
-    });
-}
-
 
 /* Note: Various places expect the allocated memory to be zeroed. */
 [[gnu::always_inline]]
@@ -99,7 +80,7 @@ Env & EvalState::allocEnv(size_t size)
 
 
 [[gnu::always_inline]]
-void EvalState::forceValue(Value & v, const Pos & pos)
+void EvalState::forceValue(Value & v, const PosIdx pos)
 {
     forceValue(v, [&]() { return pos; });
 }
@@ -128,7 +109,7 @@ void EvalState::forceValue(Value & v, Callable getPos)
 
 
 [[gnu::always_inline]]
-inline void EvalState::forceAttrs(Value & v, const Pos & pos)
+inline void EvalState::forceAttrs(Value & v, const PosIdx pos)
 {
     forceAttrs(v, [&]() { return pos; });
 }
@@ -145,7 +126,7 @@ inline void EvalState::forceAttrs(Value & v, Callable getPos)
 
 
 [[gnu::always_inline]]
-inline void EvalState::forceList(Value & v, const Pos & pos)
+inline void EvalState::forceList(Value & v, const PosIdx pos)
 {
     forceValue(v, pos);
     if (!v.isList())

src/libexpr/eval.cc

@@ -96,7 +96,8 @@ RootValue allocRootValue(Value * v)
 }
 
 
-void Value::print(std::ostream & str, std::set<const void *> * seen) const
+void Value::print(const SymbolTable & symbols, std::ostream & str,
+    std::set<const void *> * seen) const
 {
     checkInterrupt();
 
@@ -129,9 +130,9 @@ void Value::print(std::ostream & str, std::set<const void *> * seen) const
             str << "«repeated»";
         else {
             str << "{ ";
-            for (auto & i : attrs->lexicographicOrder()) {
+            for (auto & i : attrs->lexicographicOrder(symbols)) {
-                str << i->name << " = ";
+                str << symbols[i->name] << " = ";
-                i->value->print(str, seen);
+                i->value->print(symbols, str, seen);
                 str << "; ";
             }
             str << "}";
@@ -146,7 +147,7 @@ void Value::print(std::ostream & str, std::set<const void *> * seen) const
         else {
             str << "[ ";
             for (auto v2 : listItems()) {
-                v2->print(str, seen);
+                v2->print(symbols, str, seen);
                 str << " ";
             }
             str << "]";
@@ -177,17 +178,18 @@ void Value::print(std::ostream & str, std::set<const void *> * seen) const
 }
 
 
-void Value::print(std::ostream & str, bool showRepeated) const
+void Value::print(const SymbolTable & symbols, std::ostream & str, bool showRepeated) const
 {
     std::set<const void *> seen;
-    print(str, showRepeated ? nullptr : &seen);
+    print(symbols, str, showRepeated ? nullptr : &seen);
 }
 
 
-std::ostream & operator << (std::ostream & str, const Value & v)
+std::string printValue(const EvalState & state, const Value & v)
 {
-    v.print(str, false);
+    std::ostringstream out;
-    return str;
+    v.print(state.symbols, out);
+    return out.str();
 }
 
 
@@ -236,10 +238,10 @@ std::string showType(const Value & v)
     }
 }
 
-Pos Value::determinePos(const Pos & pos) const
+PosIdx Value::determinePos(const PosIdx pos) const
 {
     switch (internalType) {
-        case tAttrs: return *attrs->pos;
+        case tAttrs: return attrs->pos;
         case tLambda: return lambda.fun->pos;
         case tApp: return app.left->determinePos(pos);
         default: return pos;
@@ -306,9 +308,9 @@ static BoehmGCStackAllocator boehmGCStackAllocator;
 #endif
 
 
-static Symbol getName(const AttrName & name, EvalState & state, Env & env)
+static SymbolIdx getName(const AttrName & name, EvalState & state, Env & env)
 {
-    if (name.symbol.set()) {
+    if (name.symbol) {
         return name.symbol;
     } else {
         Value nameValue;
@@ -639,20 +641,20 @@ Value * EvalState::addPrimOp(const std::string & name,
     size_t arity, PrimOpFun primOp)
 {
     auto name2 = name.substr(0, 2) == "__" ? name.substr(2) : name;
-    Symbol sym = symbols.create(name2);
+    auto sym = symbols.create(name2);
 
     /* Hack to make constants lazy: turn them into a application of
        the primop to a dummy value. */
     if (arity == 0) {
         auto vPrimOp = allocValue();
-        vPrimOp->mkPrimOp(new PrimOp { .fun = primOp, .arity = 1, .name = sym });
+        vPrimOp->mkPrimOp(new PrimOp { .fun = primOp, .arity = 1, .name = name2 });
         Value v;
         v.mkApp(vPrimOp, vPrimOp);
         return addConstant(name, v);
     }
 
     Value * v = allocValue();
-    v->mkPrimOp(new PrimOp { .fun = primOp, .arity = arity, .name = sym });
+    v->mkPrimOp(new PrimOp { .fun = primOp, .arity = arity, .name = name2 });
     staticBaseEnv.vars.emplace_back(symbols.create(name), baseEnvDispl);
     baseEnv.values[baseEnvDispl++] = v;
     baseEnv.values[0]->attrs->push_back(Attr(sym, v));
@@ -667,21 +669,21 @@ Value * EvalState::addPrimOp(PrimOp && primOp)
     if (primOp.arity == 0) {
         primOp.arity = 1;
         auto vPrimOp = allocValue();
-        vPrimOp->mkPrimOp(new PrimOp(std::move(primOp)));
+        vPrimOp->mkPrimOp(new PrimOp(primOp));
         Value v;
         v.mkApp(vPrimOp, vPrimOp);
         return addConstant(primOp.name, v);
     }
 
-    Symbol envName = primOp.name;
+    auto envName = symbols.create(primOp.name);
     if (hasPrefix(primOp.name, "__"))
-        primOp.name = symbols.create(std::string(primOp.name, 2));
+        primOp.name = primOp.name.substr(2);
 
     Value * v = allocValue();
-    v->mkPrimOp(new PrimOp(std::move(primOp)));
+    v->mkPrimOp(new PrimOp(primOp));
     staticBaseEnv.vars.emplace_back(envName, baseEnvDispl);
     baseEnv.values[baseEnvDispl++] = v;
-    baseEnv.values[0]->attrs->push_back(Attr(primOp.name, v));
+    baseEnv.values[0]->attrs->push_back(Attr(symbols.create(primOp.name), v));
     return v;
 }
 
@@ -698,7 +700,7 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
         auto v2 = &v;
         if (v2->primOp->doc)
             return Doc {
-                .pos = noPos,
+                .pos = {},
                 .name = v2->primOp->name,
                 .arity = v2->primOp->arity,
                 .args = v2->primOp->args,
@@ -714,113 +716,133 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
    evaluator.  So here are some helper functions for throwing
    exceptions. */
 
-LocalNoInlineNoReturn(void throwEvalError(const char * s, const std::string & s2))
+void EvalState::throwEvalError(const PosIdx pos, const char * s) const
+{
+    throw EvalError({
+        .msg = hintfmt(s),
+        .errPos = positions[pos]
+    });
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s, const Value & v) const
+{
+    throw TypeError({
+        .msg = hintfmt(s, showType(v)),
+        .errPos = positions[pos]
+    });
+}
+
+void EvalState::throwEvalError(const char * s, const std::string & s2) const
 {
     throw EvalError(s, s2);
 }
 
-LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const Suggestions & suggestions, const char * s, const std::string & s2))
+void EvalState::throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s,
+    const std::string & s2) const
 {
     throw EvalError(ErrorInfo {
         .msg = hintfmt(s, s2),
-        .errPos = pos,
+        .errPos = positions[pos],
         .suggestions = suggestions,
     });
 }
 
-LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const std::string & s2))
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2) const
 {
     throw EvalError(ErrorInfo {
         .msg = hintfmt(s, s2),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 
-LocalNoInlineNoReturn(void throwEvalError(const char * s, const std::string & s2, const std::string & s3))
+void EvalState::throwEvalError(const char * s, const std::string & s2, const std::string & s3) const
 {
     throw EvalError(s, s2, s3);
 }
 
-LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const std::string & s2, const std::string & s3))
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2,
+    const std::string & s3) const
 {
     throw EvalError({
         .msg = hintfmt(s, s2, s3),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 
-LocalNoInlineNoReturn(void throwEvalError(const Pos & p1, const char * s, const Symbol & sym, const Pos & p2))
+void EvalState::throwEvalError(const PosIdx p1, const char * s, const SymbolIdx sym, const PosIdx p2) const
 {
     // p1 is where the error occurred; p2 is a position mentioned in the message.
     throw EvalError({
-        .msg = hintfmt(s, sym, p2),
+        .msg = hintfmt(s, symbols[sym], positions[p2]),
-        .errPos = p1
+        .errPos = positions[p1]
     });
 }
 
-LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const char * s))
+void EvalState::throwTypeError(const PosIdx pos, const char * s) const
 {
     throw TypeError({
         .msg = hintfmt(s),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 
-LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const char * s, const ExprLambda & fun, const Symbol & s2))
+void EvalState::throwTypeError(const PosIdx pos, const char * s, const ExprLambda & fun,
+    const SymbolIdx s2) const
 {
     throw TypeError({
-        .msg = hintfmt(s, fun.showNamePos(), s2),
+        .msg = hintfmt(s, fun.showNamePos(*this), symbols[s2]),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 
-LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const Suggestions & suggestions, const char * s, const ExprLambda & fun, const Symbol & s2))
+void EvalState::throwTypeError(const PosIdx pos, const Suggestions & suggestions, const char * s,
+    const ExprLambda & fun, const SymbolIdx s2) const
 {
     throw TypeError(ErrorInfo {
-        .msg = hintfmt(s, fun.showNamePos(), s2),
+        .msg = hintfmt(s, fun.showNamePos(*this), symbols[s2]),
-        .errPos = pos,
+        .errPos = positions[pos],
         .suggestions = suggestions,
     });
 }
 
 
-LocalNoInlineNoReturn(void throwTypeError(const char * s, const Value & v))
+void EvalState::throwTypeError(const char * s, const Value & v) const
 {
     throw TypeError(s, showType(v));
 }
 
-LocalNoInlineNoReturn(void throwAssertionError(const Pos & pos, const char * s, const std::string & s1))
+void EvalState::throwAssertionError(const PosIdx pos, const char * s, const std::string & s1) const
 {
     throw AssertionError({
         .msg = hintfmt(s, s1),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 
-LocalNoInlineNoReturn(void throwUndefinedVarError(const Pos & pos, const char * s, const std::string & s1))
+void EvalState::throwUndefinedVarError(const PosIdx pos, const char * s, const std::string & s1) const
 {
     throw UndefinedVarError({
         .msg = hintfmt(s, s1),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 
-LocalNoInlineNoReturn(void throwMissingArgumentError(const Pos & pos, const char * s, const std::string & s1))
+void EvalState::throwMissingArgumentError(const PosIdx pos, const char * s, const std::string & s1) const
 {
     throw MissingArgumentError({
         .msg = hintfmt(s, s1),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 
-LocalNoInline(void addErrorTrace(Error & e, const char * s, const std::string & s2))
+void EvalState::addErrorTrace(Error & e, const char * s, const std::string & s2) const
 {
     e.addTrace(std::nullopt, s, s2);
 }
 
-LocalNoInline(void addErrorTrace(Error & e, const Pos & pos, const char * s, const std::string & s2))
+void EvalState::addErrorTrace(Error & e, const PosIdx pos, const char * s, const std::string & s2) const
 {
-    e.addTrace(pos, s, s2);
+    e.addTrace(positions[pos], s, s2);
 }
 
 
@@ -877,11 +899,11 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
         }
         Bindings::iterator j = env->values[0]->attrs->find(var.name);
         if (j != env->values[0]->attrs->end()) {
-            if (countCalls) attrSelects[*j->pos]++;
+            if (countCalls) attrSelects[j->pos]++;
             return j->value;
         }
         if (!env->prevWith)
-            throwUndefinedVarError(var.pos, "undefined variable '%1%'", var.name);
+            throwUndefinedVarError(var.pos, "undefined variable '%1%'", symbols[var.name]);
         for (size_t l = env->prevWith; l; --l, env = env->up) ;
     }
 }
@@ -911,13 +933,14 @@ void EvalState::mkThunk_(Value & v, Expr * expr)
 }
 
 
-void EvalState::mkPos(Value & v, ptr<Pos> pos)
+void EvalState::mkPos(Value & v, PosIdx p)
 {
-    if (pos->file.set()) {
+    auto pos = positions[p];
+    if (!pos.file.empty()) {
         auto attrs = buildBindings(3);
-        attrs.alloc(sFile).mkString(pos->file);
+        attrs.alloc(sFile).mkString(pos.file);
-        attrs.alloc(sLine).mkInt(pos->line);
+        attrs.alloc(sLine).mkInt(pos.line);
-        attrs.alloc(sColumn).mkInt(pos->column);
+        attrs.alloc(sColumn).mkInt(pos.column);
         v.mkAttrs(attrs);
     } else
         v.mkNull();
@@ -1050,7 +1073,7 @@ inline bool EvalState::evalBool(Env & env, Expr * e)
 }
 
 
-inline bool EvalState::evalBool(Env & env, Expr * e, const Pos & pos)
+inline bool EvalState::evalBool(Env & env, Expr * e, const PosIdx pos)
 {
     Value v;
     e->eval(*this, env, v);
@@ -1124,7 +1147,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
             } else
                 vAttr = i.second.e->maybeThunk(state, i.second.inherited ? env : env2);
             env2.values[displ++] = vAttr;
-            v.attrs->push_back(Attr(i.first, vAttr, ptr(&i.second.pos)));
+            v.attrs->push_back(Attr(i.first, vAttr, i.second.pos));
         }
 
         /* If the rec contains an attribute called `__overrides', then
@@ -1156,7 +1179,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 
     else
         for (auto & i : attrs)
-            v.attrs->push_back(Attr(i.first, i.second.e->maybeThunk(state, env), ptr(&i.second.pos)));
+            v.attrs->push_back(Attr(i.first, i.second.e->maybeThunk(state, env), i.second.pos));
 
     /* Dynamic attrs apply *after* rec and __overrides. */
     for (auto & i : dynamicAttrs) {
@@ -1166,18 +1189,18 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         if (nameVal.type() == nNull)
             continue;
         state.forceStringNoCtx(nameVal);
-        Symbol nameSym = state.symbols.create(nameVal.string.s);
+        auto nameSym = state.symbols.create(nameVal.string.s);
         Bindings::iterator j = v.attrs->find(nameSym);
         if (j != v.attrs->end())
-            throwEvalError(i.pos, "dynamic attribute '%1%' already defined at %2%", nameSym, *j->pos);
+            state.throwEvalError(i.pos, "dynamic attribute '%1%' already defined at %2%", nameSym, j->pos);
 
         i.valueExpr->setName(nameSym);
         /* Keep sorted order so find can catch duplicates */
-        v.attrs->push_back(Attr(nameSym, i.valueExpr->maybeThunk(state, *dynamicEnv), ptr(&i.pos)));
+        v.attrs->push_back(Attr(nameSym, i.valueExpr->maybeThunk(state, *dynamicEnv), i.pos));
         v.attrs->sort(); // FIXME: inefficient
     }
 
-    v.attrs->pos = ptr(&pos);
+    v.attrs->pos = pos;
 }
 
 
@@ -1222,10 +1245,12 @@ static std::string showAttrPath(EvalState & state, Env & env, const AttrPath & a
     for (auto & i : attrPath) {
         if (!first) out << '.'; else first = false;
         try {
-            out << getName(i, state, env);
+            out << state.symbols[getName(i, state, env)];
         } catch (Error & e) {
-            assert(!i.symbol.set());
+            assert(!i.symbol);
-            out << "\"${" << *i.expr << "}\"";
+            out << "\"${";
+            i.expr->show(state.symbols, out);
+            out << "}\"";
         }
     }
     return out.str();
@@ -1235,7 +1260,7 @@ static std::string showAttrPath(EvalState & state, Env & env, const AttrPath & a
 void ExprSelect::eval(EvalState & state, Env & env, Value & v)
 {
     Value vTmp;
-    ptr<Pos> pos2(&noPos);
+    PosIdx pos2;
     Value * vAttrs = &vTmp;
 
     e->eval(state, env, vTmp);
@@ -1245,7 +1270,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
         for (auto & i : attrPath) {
             state.nrLookups++;
             Bindings::iterator j;
-            Symbol name = getName(i, state, env);
+            auto name = getName(i, state, env);
             if (def) {
                 state.forceValue(*vAttrs, pos);
                 if (vAttrs->type() != nAttrs ||
@@ -1259,23 +1284,24 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                 if ((j = vAttrs->attrs->find(name)) == vAttrs->attrs->end()) {
                     std::set<std::string> allAttrNames;
                     for (auto & attr : *vAttrs->attrs)
-                        allAttrNames.insert(attr.name);
+                        allAttrNames.insert(state.symbols[attr.name]);
-                    throwEvalError(
+                    state.throwEvalError(
                         pos,
-                        Suggestions::bestMatches(allAttrNames, name),
+                        Suggestions::bestMatches(allAttrNames, state.symbols[name]),
-                        "attribute '%1%' missing", name);
+                        "attribute '%1%' missing", state.symbols[name]);
                 }
             }
             vAttrs = j->value;
             pos2 = j->pos;
-            if (state.countCalls) state.attrSelects[*pos2]++;
+            if (state.countCalls) state.attrSelects[pos2]++;
         }
 
-        state.forceValue(*vAttrs, (*pos2 != noPos ? *pos2 : this->pos ) );
+        state.forceValue(*vAttrs, (pos2 ? pos2 : this->pos ) );
 
     } catch (Error & e) {
-        if (*pos2 != noPos && pos2->file != state.sDerivationNix)
+        auto pos2r = state.positions[pos2];
-            addErrorTrace(e, *pos2, "while evaluating the attribute '%1%'",
+        if (pos2 && pos2r.file != state.derivationNixPath)
+            state.addErrorTrace(e, pos2, "while evaluating the attribute '%1%'",
                 showAttrPath(state, env, attrPath));
         throw;
     }
@@ -1294,7 +1320,7 @@ void ExprOpHasAttr::eval(EvalState & state, Env & env, Value & v)
     for (auto & i : attrPath) {
         state.forceValue(*vAttrs, noPos);
         Bindings::iterator j;
-        Symbol name = getName(i, state, env);
+        auto name = getName(i, state, env);
         if (vAttrs->type() != nAttrs ||
             (j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
         {
@@ -1315,9 +1341,11 @@ void ExprLambda::eval(EvalState & state, Env & env, Value & v)
 }
 
 
-void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const Pos & pos)
+void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const PosIdx pos)
 {
-    auto trace = evalSettings.traceFunctionCalls ? std::make_unique<FunctionCallTrace>(pos) : nullptr;
+    auto trace = evalSettings.traceFunctionCalls
+        ? std::make_unique<FunctionCallTrace>(positions[pos])
+        : nullptr;
 
     forceValue(fun, pos);
 
@@ -1342,7 +1370,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
             ExprLambda & lambda(*vCur.lambda.fun);
 
             auto size =
-                (lambda.arg.empty() ? 0 : 1) +
+                (!lambda.arg ? 0 : 1) +
                 (lambda.hasFormals() ? lambda.formals->formals.size() : 0);
             Env & env2(allocEnv(size));
             env2.up = vCur.lambda.env;
@@ -1355,7 +1383,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
             else {
                 forceAttrs(*args[0], pos);
 
-                if (!lambda.arg.empty())
+                if (lambda.arg)
                     env2.values[displ++] = args[0];
 
                 /* For each formal argument, get the actual argument.  If
@@ -1383,10 +1411,10 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                         if (!lambda.formals->has(i.name)) {
                             std::set<std::string> formalNames;
                             for (auto & formal : lambda.formals->formals)
-                                formalNames.insert(formal.name);
+                                formalNames.insert(symbols[formal.name]);
                             throwTypeError(
                                 pos,
-                                Suggestions::bestMatches(formalNames, i.name),
+                                Suggestions::bestMatches(formalNames, symbols[i.name]),
                                 "%1% called with unexpected argument '%2%'",
                                 lambda,
                                 i.name);
@@ -1404,8 +1432,8 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
             } catch (Error & e) {
                 if (loggerSettings.showTrace.get()) {
                     addErrorTrace(e, lambda.pos, "while evaluating %s",
-                        (lambda.name.set()
+                        (lambda.name
-                            ? "'" + (const std::string &) lambda.name + "'"
+                            ? concatStrings("'", symbols[lambda.name], "'")
                             : "anonymous lambda"));
                     addErrorTrace(e, pos, "from call site%s", "");
                 }
@@ -1554,7 +1582,7 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
 Nix attempted to evaluate a function as a top level expression; in
 this case it must have its arguments supplied either by default
 values, or passed explicitly with '--arg' or '--argstr'. See
-https://nixos.org/manual/nix/stable/#ss-functions.)", i.name);
+https://nixos.org/manual/nix/stable/#ss-functions.)", symbols[i.name]);
 
             }
         }
@@ -1586,8 +1614,8 @@ void ExprAssert::eval(EvalState & state, Env & env, Value & v)
 {
     if (!state.evalBool(env, cond, pos)) {
         std::ostringstream out;
-        cond->show(out);
+        cond->show(state.symbols, out);
-        throwAssertionError(pos, "assertion '%1%' failed", out.str());
+        state.throwAssertionError(pos, "assertion '%1%' failed", out.str());
     }
     body->eval(state, env, v);
 }
@@ -1680,7 +1708,7 @@ void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v)
 }
 
 
-void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const Pos & pos)
+void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos)
 {
     nrListConcats++;
 
@@ -1764,14 +1792,14 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
                 nf = n;
                 nf += vTmp.fpoint;
             } else
-                throwEvalError(i_pos, "cannot add %1% to an integer", showType(vTmp));
+                state.throwEvalError(i_pos, "cannot add %1% to an integer", showType(vTmp));
         } else if (firstType == nFloat) {
             if (vTmp.type() == nInt) {
                 nf += vTmp.integer;
             } else if (vTmp.type() == nFloat) {
                 nf += vTmp.fpoint;
             } else
-                throwEvalError(i_pos, "cannot add %1% to a float", showType(vTmp));
+                state.throwEvalError(i_pos, "cannot add %1% to a float", showType(vTmp));
         } else {
             if (s.empty()) s.reserve(es->size());
             /* skip canonization of first path, which would only be not
@@ -1791,7 +1819,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
         v.mkFloat(nf);
     else if (firstType == nPath) {
         if (!context.empty())
-            throwEvalError(pos, "a string that refers to a store path cannot be appended to a path");
+            state.throwEvalError(pos, "a string that refers to a store path cannot be appended to a path");
         v.mkPath(canonPath(str()));
     } else
         v.mkStringMove(c_str(), context);
@@ -1800,7 +1828,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
 
 void ExprPos::eval(EvalState & state, Env & env, Value & v)
 {
-    state.mkPos(v, ptr(&pos));
+    state.mkPos(v, pos);
 }
 
 
@@ -1820,7 +1848,7 @@ void EvalState::forceValueDeep(Value & v)
                 try {
                     recurse(*i.value);
                 } catch (Error & e) {
-                    addErrorTrace(e, *i.pos, "while evaluating the attribute '%1%'", i.name);
+                    addErrorTrace(e, i.pos, "while evaluating the attribute '%1%'", symbols[i.name]);
                     throw;
                 }
         }
@@ -1835,7 +1863,7 @@ void EvalState::forceValueDeep(Value & v)
 }
 
 
-NixInt EvalState::forceInt(Value & v, const Pos & pos)
+NixInt EvalState::forceInt(Value & v, const PosIdx pos)
 {
     forceValue(v, pos);
     if (v.type() != nInt)
@@ -1844,7 +1872,7 @@ NixInt EvalState::forceInt(Value & v, const Pos & pos)
 }
 
 
-NixFloat EvalState::forceFloat(Value & v, const Pos & pos)
+NixFloat EvalState::forceFloat(Value & v, const PosIdx pos)
 {
     forceValue(v, pos);
     if (v.type() == nInt)
@@ -1855,7 +1883,7 @@ NixFloat EvalState::forceFloat(Value & v, const Pos & pos)
 }
 
 
-bool EvalState::forceBool(Value & v, const Pos & pos)
+bool EvalState::forceBool(Value & v, const PosIdx pos)
 {
     forceValue(v, pos);
     if (v.type() != nBool)
@@ -1870,7 +1898,7 @@ bool EvalState::isFunctor(Value & fun)
 }
 
 
-void EvalState::forceFunction(Value & v, const Pos & pos)
+void EvalState::forceFunction(Value & v, const PosIdx pos)
 {
     forceValue(v, pos);
     if (v.type() != nFunction && !isFunctor(v))
@@ -1878,7 +1906,7 @@ void EvalState::forceFunction(Value & v, const Pos & pos)
 }
 
 
-std::string_view EvalState::forceString(Value & v, const Pos & pos)
+std::string_view EvalState::forceString(Value & v, const PosIdx pos)
 {
     forceValue(v, pos);
     if (v.type() != nString) {
@@ -1931,7 +1959,7 @@ NixStringContext Value::getContext(const Store & store)
 }
 
 
-std::string_view EvalState::forceString(Value & v, PathSet & context, const Pos & pos)
+std::string_view EvalState::forceString(Value & v, PathSet & context, const PosIdx pos)
 {
     auto s = forceString(v, pos);
     copyContext(v, context);
@@ -1939,7 +1967,7 @@ std::string_view EvalState::forceString(Value & v, PathSet & context, const Pos
 }
 
 
-std::string_view EvalState::forceStringNoCtx(Value & v, const Pos & pos)
+std::string_view EvalState::forceStringNoCtx(Value & v, const PosIdx pos)
 {
     auto s = forceString(v, pos);
     if (v.string.context) {
@@ -1959,13 +1987,13 @@ bool EvalState::isDerivation(Value & v)
     if (v.type() != nAttrs) return false;
     Bindings::iterator i = v.attrs->find(sType);
     if (i == v.attrs->end()) return false;
-    forceValue(*i->value, *i->pos);
+    forceValue(*i->value, i->pos);
     if (i->value->type() != nString) return false;
     return strcmp(i->value->string.s, "derivation") == 0;
 }
 
 
-std::optional<std::string> EvalState::tryAttrsToString(const Pos & pos, Value & v,
+std::optional<std::string> EvalState::tryAttrsToString(const PosIdx pos, Value & v,
     PathSet & context, bool coerceMore, bool copyToStore)
 {
     auto i = v.attrs->find(sToString);
@@ -1978,7 +2006,7 @@ std::optional<std::string> EvalState::tryAttrsToString(const Pos & pos, Value &
     return {};
 }
 
-BackedStringView EvalState::coerceToString(const Pos & pos, Value & v, PathSet & context,
+BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet & context,
     bool coerceMore, bool copyToStore, bool canonicalizePath)
 {
     forceValue(v, pos);
@@ -2007,7 +2035,7 @@ BackedStringView EvalState::coerceToString(const Pos & pos, Value & v, PathSet &
     }
 
     if (v.type() == nExternal)
-        return v.external->coerceToString(pos, context, coerceMore, copyToStore);
+        return v.external->coerceToString(positions[pos], context, coerceMore, copyToStore);
 
     if (coerceMore) {
 
@@ -2060,7 +2088,7 @@ std::string EvalState::copyPathToStore(PathSet & context, const Path & path)
 }
 
 
-Path EvalState::coerceToPath(const Pos & pos, Value & v, PathSet & context)
+Path EvalState::coerceToPath(const PosIdx pos, Value & v, PathSet & context)
 {
     auto path = coerceToString(pos, v, context, false, false).toOwned();
     if (path == "" || path[0] != '/')
@@ -2069,14 +2097,14 @@ Path EvalState::coerceToPath(const Pos & pos, Value & v, PathSet & context)
 }
 
 
-StorePath EvalState::coerceToStorePath(const Pos & pos, Value & v, PathSet & context)
+StorePath EvalState::coerceToStorePath(const PosIdx pos, Value & v, PathSet & context)
 {
     auto path = coerceToString(pos, v, context, false, false).toOwned();
     if (auto storePath = store->maybeParseStorePath(path))
         return *storePath;
     throw EvalError({
         .msg = hintfmt("path '%1%' is not in the Nix store", path),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 
@@ -2243,14 +2271,14 @@ void EvalState::printStats()
                 auto list = topObj.list("functions");
                 for (auto & i : functionCalls) {
                     auto obj = list.object();
-                    if (i.first->name.set())
+                    if (i.first->name)
                         obj.attr("name", (const std::string &) i.first->name);
                     else
                         obj.attr("name", nullptr);
-                    if (i.first->pos) {
+                    if (auto pos = positions[i.first->pos]) {
-                        obj.attr("file", (const std::string &) i.first->pos.file);
+                        obj.attr("file", (const std::string &) pos.file);
-                        obj.attr("line", i.first->pos.line);
+                        obj.attr("line", pos.line);
-                        obj.attr("column", i.first->pos.column);
+                        obj.attr("column", pos.column);
                     }
                     obj.attr("count", i.second);
                 }
@@ -2259,10 +2287,10 @@ void EvalState::printStats()
                 auto list = topObj.list("attributes");
                 for (auto & i : attrSelects) {
                     auto obj = list.object();
-                    if (i.first) {
+                    if (auto pos = positions[i.first]) {
-                        obj.attr("file", (const std::string &) i.first.file);
+                        obj.attr("file", (const std::string &) pos.file);
-                        obj.attr("line", i.first.line);
+                        obj.attr("line", pos.line);
-                        obj.attr("column", i.first.column);
+                        obj.attr("column", pos.column);
                     }
                     obj.attr("count", i.second);
                 }

src/libexpr/eval.hh

@@ -23,14 +23,14 @@ class StorePath;
 enum RepairFlag : bool;
 
 
-typedef void (* PrimOpFun) (EvalState & state, const Pos & pos, Value * * args, Value & v);
+typedef void (* PrimOpFun) (EvalState & state, const PosIdx pos, Value * * args, Value & v);
 
 
 struct PrimOp
 {
     PrimOpFun fun;
     size_t arity;
-    Symbol name;
+    std::string name;
     std::vector<std::string> args;
     const char * doc = nullptr;
 };
@@ -53,7 +53,8 @@ void copyContext(const Value & v, PathSet & context);
 typedef std::map<Path, StorePath> SrcToStore;
 
 
-std::ostream & operator << (std::ostream & str, const Value & v);
+std::ostream & printValue(const EvalState & state, std::ostream & str, const Value & v);
+std::string printValue(const EvalState & state, const Value & v);
 
 
 typedef std::pair<std::string, std::string> SearchPathElem;
@@ -73,8 +74,11 @@ class EvalState
 {
 public:
     SymbolTable symbols;
+    PosTable positions;
 
-    const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sValue,
+    static inline std::string derivationNixPath = "//builtin/derivation.nix";
+
+    const SymbolIdx sWith, sOutPath, sDrvPath, sType, sMeta, sName, sValue,
         sSystem, sOverrides, sOutputs, sOutputName, sIgnoreNulls,
         sFile, sLine, sColumn, sFunctor, sToString,
         sRight, sWrong, sStructuredAttrs, sBuilder, sArgs,
@@ -83,7 +87,7 @@ public:
         sRecurseForDerivations,
         sDescription, sSelf, sEpsilon, sStartSet, sOperator, sKey, sPath,
         sPrefix;
-    Symbol sDerivationNix;
+    SymbolIdx sDerivationNix;
 
     /* If set, force copying files to the Nix store even if they
        already exist there. */
@@ -205,7 +209,7 @@ public:
 
     /* Look up a file in the search path. */
     Path findFile(const std::string_view path);
-    Path findFile(SearchPath & searchPath, const std::string_view path, const Pos & pos = noPos);
+    Path findFile(SearchPath & searchPath, const std::string_view path, const PosIdx pos = noPos);
 
     /* If the specified search path element is a URI, download it. */
     std::pair<bool, std::string> resolveSearchPathElem(const SearchPathElem & elem);
@@ -217,14 +221,14 @@ public:
     /* Evaluation the expression, then verify that it has the expected
        type. */
     inline bool evalBool(Env & env, Expr * e);
-    inline bool evalBool(Env & env, Expr * e, const Pos & pos);
+    inline bool evalBool(Env & env, Expr * e, const PosIdx pos);
     inline void evalAttrs(Env & env, Expr * e, Value & v);
 
     /* If `v' is a thunk, enter it and overwrite `v' with the result
        of the evaluation of the thunk.  If `v' is a delayed function
        application, call the function and overwrite `v' with the
        result.  Otherwise, this is a no-op. */
-    inline void forceValue(Value & v, const Pos & pos);
+    inline void forceValue(Value & v, const PosIdx pos);
 
     template <typename Callable>
     inline void forceValue(Value & v, Callable getPos);
@@ -234,33 +238,72 @@ public:
     void forceValueDeep(Value & v);
 
     /* Force `v', and then verify that it has the expected type. */
-    NixInt forceInt(Value & v, const Pos & pos);
+    NixInt forceInt(Value & v, const PosIdx pos);
-    NixFloat forceFloat(Value & v, const Pos & pos);
+    NixFloat forceFloat(Value & v, const PosIdx pos);
-    bool forceBool(Value & v, const Pos & pos);
+    bool forceBool(Value & v, const PosIdx pos);
 
-    void forceAttrs(Value & v, const Pos & pos);
+    void forceAttrs(Value & v, const PosIdx pos);
 
     template <typename Callable>
     inline void forceAttrs(Value & v, Callable getPos);
 
-    inline void forceList(Value & v, const Pos & pos);
+    inline void forceList(Value & v, const PosIdx pos);
-    void forceFunction(Value & v, const Pos & pos); // either lambda or primop
+    void forceFunction(Value & v, const PosIdx pos); // either lambda or primop
-    std::string_view forceString(Value & v, const Pos & pos = noPos);
+    std::string_view forceString(Value & v, const PosIdx pos = noPos);
-    std::string_view forceString(Value & v, PathSet & context, const Pos & pos = noPos);
+    std::string_view forceString(Value & v, PathSet & context, const PosIdx pos = noPos);
-    std::string_view forceStringNoCtx(Value & v, const Pos & pos = noPos);
+    std::string_view forceStringNoCtx(Value & v, const PosIdx pos = noPos);
 
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const Value & v) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s,
+        const std::string & s2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2, const std::string & s3) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2, const std::string & s3) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx p1, const char * s, const SymbolIdx sym, const PosIdx p2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const ExprLambda & fun, const SymbolIdx s2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const Suggestions & suggestions, const char * s,
+        const ExprLambda & fun, const SymbolIdx s2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const char * s, const Value & v) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwAssertionError(const PosIdx pos, const char * s, const std::string & s1) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwUndefinedVarError(const PosIdx pos, const char * s, const std::string & s1) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwMissingArgumentError(const PosIdx pos, const char * s, const std::string & s1) const;
+
+    [[gnu::noinline]]
+    void addErrorTrace(Error & e, const char * s, const std::string & s2) const;
+    [[gnu::noinline]]
+    void addErrorTrace(Error & e, const PosIdx pos, const char * s, const std::string & s2) const;
+
+public:
     /* Return true iff the value `v' denotes a derivation (i.e. a
        set with attribute `type = "derivation"'). */
     bool isDerivation(Value & v);
 
-    std::optional<std::string> tryAttrsToString(const Pos & pos, Value & v,
+    std::optional<std::string> tryAttrsToString(const PosIdx pos, Value & v,
         PathSet & context, bool coerceMore = false, bool copyToStore = true);
 
     /* String coercion.  Converts strings, paths and derivations to a
        string.  If `coerceMore' is set, also converts nulls, integers,
        booleans and lists to a string.  If `copyToStore' is set,
        referenced paths are copied to the Nix store as a side effect. */
-    BackedStringView coerceToString(const Pos & pos, Value & v, PathSet & context,
+    BackedStringView coerceToString(const PosIdx pos, Value & v, PathSet & context,
         bool coerceMore = false, bool copyToStore = true,
         bool canonicalizePath = true);
 
@@ -269,10 +312,10 @@ public:
     /* Path coercion.  Converts strings, paths and derivations to a
        path.  The result is guaranteed to be a canonicalised, absolute
        path.  Nothing is copied to the store. */
-    Path coerceToPath(const Pos & pos, Value & v, PathSet & context);
+    Path coerceToPath(const PosIdx pos, Value & v, PathSet & context);
 
     /* Like coerceToPath, but the result must be a store path. */
-    StorePath coerceToStorePath(const Pos & pos, Value & v, PathSet & context);
+    StorePath coerceToStorePath(const PosIdx pos, Value & v, PathSet & context);
 
 public:
 
@@ -305,7 +348,7 @@ public:
     struct Doc
     {
         Pos pos;
-        std::optional<Symbol> name;
+        std::optional<std::string> name;
         size_t arity;
         std::vector<std::string> args;
         const char * doc;
@@ -333,9 +376,9 @@ public:
     bool isFunctor(Value & fun);
 
     // FIXME: use std::span
-    void callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const Pos & pos);
+    void callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const PosIdx pos);
 
-    void callFunction(Value & fun, Value & arg, Value & vRes, const Pos & pos)
+    void callFunction(Value & fun, Value & arg, Value & vRes, const PosIdx pos)
     {
         Value * args[] = {&arg};
         callFunction(fun, 1, args, vRes, pos);
@@ -349,7 +392,7 @@ public:
     inline Value * allocValue();
     inline Env & allocEnv(size_t size);
 
-    Value * allocAttr(Value & vAttrs, const Symbol & name);
+    Value * allocAttr(Value & vAttrs, const SymbolIdx & name);
     Value * allocAttr(Value & vAttrs, std::string_view name);
 
     Bindings * allocBindings(size_t capacity);
@@ -361,9 +404,9 @@ public:
 
     void mkList(Value & v, size_t length);
     void mkThunk_(Value & v, Expr * expr);
-    void mkPos(Value & v, ptr<Pos> pos);
+    void mkPos(Value & v, PosIdx pos);
 
-    void concatLists(Value & v, size_t nrLists, Value * * lists, const Pos & pos);
+    void concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos);
 
     /* Print statistics. */
     void printStats();
@@ -391,7 +434,7 @@ private:
 
     bool countCalls;
 
-    typedef std::map<Symbol, size_t> PrimOpCalls;
+    typedef std::map<std::string, size_t> PrimOpCalls;
     PrimOpCalls primOpCalls;
 
     typedef std::map<ExprLambda *, size_t> FunctionCalls;
@@ -399,7 +442,7 @@ private:
 
     void incrFunctionCall(ExprLambda * fun);
 
-    typedef std::map<Pos, size_t> AttrSelects;
+    typedef std::map<PosIdx, size_t> AttrSelects;
     AttrSelects attrSelects;
 
     friend struct ExprOpUpdate;
@@ -410,9 +453,9 @@ private:
     friend struct ExprFloat;
     friend struct ExprPath;
     friend struct ExprSelect;
-    friend void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v);
+    friend void prim_getAttr(EvalState & state, const PosIdx pos, Value * * args, Value & v);
-    friend void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v);
+    friend void prim_match(EvalState & state, const PosIdx pos, Value * * args, Value & v);
-    friend void prim_split(EvalState & state, const Pos & pos, Value * * args, Value & v);
+    friend void prim_split(EvalState & state, const PosIdx pos, Value * * args, Value & v);
 
     friend struct Value;
 };

src/libexpr/flake/flake.cc

@@ -72,7 +72,7 @@ static std::tuple<fetchers::Tree, FlakeRef, FlakeRef> fetchOrSubstituteTree(
     return {std::move(tree), resolvedRef, lockedRef};
 }
 
-static void forceTrivialValue(EvalState & state, Value & value, const Pos & pos)
+static void forceTrivialValue(EvalState & state, Value & value, const PosIdx pos)
 {
     if (value.isThunk() && value.isTrivial())
         state.forceValue(value, pos);
@@ -80,20 +80,20 @@ static void forceTrivialValue(EvalState & state, Value & value, const Pos & pos)
 
 
 static void expectType(EvalState & state, ValueType type,
-    Value & value, const Pos & pos)
+    Value & value, const PosIdx pos)
 {
     forceTrivialValue(state, value, pos);
     if (value.type() != type)
         throw Error("expected %s but got %s at %s",
-            showType(type), showType(value.type()), pos);
+            showType(type), showType(value.type()), state.positions[pos]);
 }
 
 static std::map<FlakeId, FlakeInput> parseFlakeInputs(
-    EvalState & state, Value * value, const Pos & pos,
+    EvalState & state, Value * value, const PosIdx pos,
     const std::optional<Path> & baseDir, InputPath lockRootPath);
 
 static FlakeInput parseFlakeInput(EvalState & state,
-    const std::string & inputName, Value * value, const Pos & pos,
+    const std::string & inputName, Value * value, const PosIdx pos,
     const std::optional<Path> & baseDir, InputPath lockRootPath)
 {
     expectType(state, nAttrs, *value, pos);
@@ -111,37 +111,39 @@ static FlakeInput parseFlakeInput(EvalState & state,
     for (nix::Attr attr : *(value->attrs)) {
         try {
             if (attr.name == sUrl) {
-                expectType(state, nString, *attr.value, *attr.pos);
+                expectType(state, nString, *attr.value, attr.pos);
                 url = attr.value->string.s;
                 attrs.emplace("url", *url);
             } else if (attr.name == sFlake) {
-                expectType(state, nBool, *attr.value, *attr.pos);
+                expectType(state, nBool, *attr.value, attr.pos);
                 input.isFlake = attr.value->boolean;
             } else if (attr.name == sInputs) {
-                input.overrides = parseFlakeInputs(state, attr.value, *attr.pos, baseDir, lockRootPath);
+                input.overrides = parseFlakeInputs(state, attr.value, attr.pos, baseDir, lockRootPath);
             } else if (attr.name == sFollows) {
-                expectType(state, nString, *attr.value, *attr.pos);
+                expectType(state, nString, *attr.value, attr.pos);
                 auto follows(parseInputPath(attr.value->string.s));
                 follows.insert(follows.begin(), lockRootPath.begin(), lockRootPath.end());
                 input.follows = follows;
             } else {
                 switch (attr.value->type()) {
                     case nString:
-                        attrs.emplace(attr.name, attr.value->string.s);
+                        attrs.emplace(state.symbols[attr.name], attr.value->string.s);
                         break;
                     case nBool:
-                        attrs.emplace(attr.name, Explicit<bool> { attr.value->boolean });
+                        attrs.emplace(state.symbols[attr.name], Explicit<bool> { attr.value->boolean });
                         break;
                     case nInt:
-                        attrs.emplace(attr.name, (long unsigned int)attr.value->integer);
+                        attrs.emplace(state.symbols[attr.name], (long unsigned int)attr.value->integer);
                         break;
                     default:
                         throw TypeError("flake input attribute '%s' is %s while a string, Boolean, or integer is expected",
-                            attr.name, showType(*attr.value));
+                            state.symbols[attr.name], showType(*attr.value));
                 }
             }
         } catch (Error & e) {
-            e.addTrace(*attr.pos, hintfmt("in flake attribute '%s'", attr.name));
+            e.addTrace(
+                state.positions[attr.pos],
+                hintfmt("in flake attribute '%s'", state.symbols[attr.name]));
             throw;
         }
     }
@@ -150,13 +152,13 @@ static FlakeInput parseFlakeInput(EvalState & state,
         try {
             input.ref = FlakeRef::fromAttrs(attrs);
         } catch (Error & e) {
-            e.addTrace(pos, hintfmt("in flake input"));
+            e.addTrace(state.positions[pos], hintfmt("in flake input"));
             throw;
         }
     else {
         attrs.erase("url");
         if (!attrs.empty())
-            throw Error("unexpected flake input attribute '%s', at %s", attrs.begin()->first, pos);
+            throw Error("unexpected flake input attribute '%s', at %s", attrs.begin()->first, state.positions[pos]);
         if (url)
             input.ref = parseFlakeRef(*url, baseDir, true, input.isFlake);
     }
@@ -168,7 +170,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
 }
 
 static std::map<FlakeId, FlakeInput> parseFlakeInputs(
-    EvalState & state, Value * value, const Pos & pos,
+    EvalState & state, Value * value, const PosIdx pos,
     const std::optional<Path> & baseDir, InputPath lockRootPath)
 {
     std::map<FlakeId, FlakeInput> inputs;
@@ -176,11 +178,11 @@ static std::map<FlakeId, FlakeInput> parseFlakeInputs(
     expectType(state, nAttrs, *value, pos);
 
     for (nix::Attr & inputAttr : *(*value).attrs) {
-        inputs.emplace(inputAttr.name,
+        inputs.emplace(state.symbols[inputAttr.name],
             parseFlakeInput(state,
-                inputAttr.name,
+                state.symbols[inputAttr.name],
                 inputAttr.value,
-                *inputAttr.pos,
+                inputAttr.pos,
                 baseDir,
                 lockRootPath));
     }
@@ -218,28 +220,28 @@ static Flake getFlake(
     Value vInfo;
     state.evalFile(flakeFile, vInfo, true); // FIXME: symlink attack
 
-    expectType(state, nAttrs, vInfo, Pos(foFile, state.symbols.create(flakeFile), 0, 0));
+    expectType(state, nAttrs, vInfo, state.positions.add({flakeFile, foFile}, 0, 0));
 
     if (auto description = vInfo.attrs->get(state.sDescription)) {
-        expectType(state, nString, *description->value, *description->pos);
+        expectType(state, nString, *description->value, description->pos);
         flake.description = description->value->string.s;
     }
 
     auto sInputs = state.symbols.create("inputs");
 
     if (auto inputs = vInfo.attrs->get(sInputs))
-        flake.inputs = parseFlakeInputs(state, inputs->value, *inputs->pos, flakeDir, lockRootPath);
+        flake.inputs = parseFlakeInputs(state, inputs->value, inputs->pos, flakeDir, lockRootPath);
 
     auto sOutputs = state.symbols.create("outputs");
 
     if (auto outputs = vInfo.attrs->get(sOutputs)) {
-        expectType(state, nFunction, *outputs->value, *outputs->pos);
+        expectType(state, nFunction, *outputs->value, outputs->pos);
 
         if (outputs->value->isLambda() && outputs->value->lambda.fun->hasFormals()) {
             for (auto & formal : outputs->value->lambda.fun->formals->formals) {
                 if (formal.name != state.sSelf)
-                    flake.inputs.emplace(formal.name, FlakeInput {
+                    flake.inputs.emplace(state.symbols[formal.name], FlakeInput {
-                        .ref = parseFlakeRef(formal.name)
+                        .ref = parseFlakeRef(state.symbols[formal.name])
                     });
             }
         }
@@ -250,35 +252,41 @@ static Flake getFlake(
     auto sNixConfig = state.symbols.create("nixConfig");
 
     if (auto nixConfig = vInfo.attrs->get(sNixConfig)) {
-        expectType(state, nAttrs, *nixConfig->value, *nixConfig->pos);
+        expectType(state, nAttrs, *nixConfig->value, nixConfig->pos);
 
         for (auto & setting : *nixConfig->value->attrs) {
-            forceTrivialValue(state, *setting.value, *setting.pos);
+            forceTrivialValue(state, *setting.value, setting.pos);
             if (setting.value->type() == nString)
-                flake.config.settings.insert({setting.name, std::string(state.forceStringNoCtx(*setting.value, *setting.pos))});
+                flake.config.settings.emplace(
+                    state.symbols[setting.name],
+                    std::string(state.forceStringNoCtx(*setting.value, setting.pos)));
             else if (setting.value->type() == nPath) {
                 PathSet emptyContext = {};
                 flake.config.settings.emplace(
-                    setting.name,
+                    state.symbols[setting.name],
-                    state.coerceToString(*setting.pos, *setting.value, emptyContext, false, true, true) .toOwned());
+                    state.coerceToString(setting.pos, *setting.value, emptyContext, false, true, true) .toOwned());
             }
             else if (setting.value->type() == nInt)
-                flake.config.settings.insert({setting.name, state.forceInt(*setting.value, *setting.pos)});
+                flake.config.settings.emplace(
+                    state.symbols[setting.name],
+                    state.forceInt(*setting.value, setting.pos));
             else if (setting.value->type() == nBool)
-                flake.config.settings.insert({setting.name, Explicit<bool> { state.forceBool(*setting.value, *setting.pos) }});
+                flake.config.settings.emplace(
+                    state.symbols[setting.name],
+                    Explicit<bool> { state.forceBool(*setting.value, setting.pos) });
             else if (setting.value->type() == nList) {
                 std::vector<std::string> ss;
                 for (auto elem : setting.value->listItems()) {
                     if (elem->type() != nString)
                         throw TypeError("list element in flake configuration setting '%s' is %s while a string is expected",
-                            setting.name, showType(*setting.value));
+                            state.symbols[setting.name], showType(*setting.value));
-                    ss.emplace_back(state.forceStringNoCtx(*elem, *setting.pos));
+                    ss.emplace_back(state.forceStringNoCtx(*elem, setting.pos));
                 }
-                flake.config.settings.insert({setting.name, ss});
+                flake.config.settings.emplace(state.symbols[setting.name], ss);
             }
             else
                 throw TypeError("flake configuration setting '%s' is %s",
-                    setting.name, showType(*setting.value));
+                    state.symbols[setting.name], showType(*setting.value));
         }
     }
 
@@ -288,7 +296,7 @@ static Flake getFlake(
             attr.name != sOutputs &&
             attr.name != sNixConfig)
             throw Error("flake '%s' has an unsupported attribute '%s', at %s",
-                lockedRef, attr.name, *attr.pos);
+                lockedRef, state.symbols[attr.name], state.positions[attr.pos]);
     }
 
     return flake;
@@ -704,12 +712,12 @@ void callFlake(EvalState & state,
     state.callFunction(*vTmp2, *vRootSubdir, vRes, noPos);
 }
 
-static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_getFlake(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     std::string flakeRefS(state.forceStringNoCtx(*args[0], pos));
     auto flakeRef = parseFlakeRef(flakeRefS, {}, true);
     if (evalSettings.pureEval && !flakeRef.input.isLocked())
-        throw Error("cannot call 'getFlake' on unlocked flake reference '%s', at %s (use --impure to override)", flakeRefS, pos);
+        throw Error("cannot call 'getFlake' on unlocked flake reference '%s', at %s (use --impure to override)", flakeRefS, state.positions[pos]);
 
     callFlake(state,
         lockFlake(state, flakeRef,

src/libexpr/function-trace.hh

@@ -8,7 +8,7 @@ namespace nix {
 
 struct FunctionCallTrace
 {
-    const Pos & pos;
+    const Pos pos;
     FunctionCallTrace(const Pos & pos);
     ~FunctionCallTrace();
 };

src/libexpr/get-drvs.cc

@@ -61,7 +61,7 @@ std::string DrvInfo::querySystem() const
 {
     if (system == "" && attrs) {
         auto i = attrs->find(state->sSystem);
-        system = i == attrs->end() ? "unknown" : state->forceStringNoCtx(*i->value, *i->pos);
+        system = i == attrs->end() ? "unknown" : state->forceStringNoCtx(*i->value, i->pos);
     }
     return system;
 }
@@ -75,7 +75,7 @@ std::optional<StorePath> DrvInfo::queryDrvPath() const
         if (i == attrs->end())
             drvPath = {std::nullopt};
         else
-            drvPath = {state->coerceToStorePath(*i->pos, *i->value, context)};
+            drvPath = {state->coerceToStorePath(i->pos, *i->value, context)};
     }
     return drvPath.value_or(std::nullopt);
 }
@@ -95,7 +95,7 @@ StorePath DrvInfo::queryOutPath() const
         Bindings::iterator i = attrs->find(state->sOutPath);
         PathSet context;
         if (i != attrs->end())
-            outPath = state->coerceToStorePath(*i->pos, *i->value, context);
+            outPath = state->coerceToStorePath(i->pos, *i->value, context);
     }
     if (!outPath)
         throw UnimplementedError("CA derivations are not yet supported");
@@ -109,23 +109,23 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
         /* Get the ‘outputs’ list. */
         Bindings::iterator i;
         if (attrs && (i = attrs->find(state->sOutputs)) != attrs->end()) {
-            state->forceList(*i->value, *i->pos);
+            state->forceList(*i->value, i->pos);
 
             /* For each output... */
             for (auto elem : i->value->listItems()) {
-                std::string output(state->forceStringNoCtx(*elem, *i->pos));
+                std::string output(state->forceStringNoCtx(*elem, i->pos));
 
                 if (withPaths) {
                     /* Evaluate the corresponding set. */
                     Bindings::iterator out = attrs->find(state->symbols.create(output));
                     if (out == attrs->end()) continue; // FIXME: throw error?
-                    state->forceAttrs(*out->value, *i->pos);
+                    state->forceAttrs(*out->value, i->pos);
 
                     /* And evaluate its ‘outPath’ attribute. */
                     Bindings::iterator outPath = out->value->attrs->find(state->sOutPath);
                     if (outPath == out->value->attrs->end()) continue; // FIXME: throw error?
                     PathSet context;
-                    outputs.emplace(output, state->coerceToStorePath(*outPath->pos, *outPath->value, context));
+                    outputs.emplace(output, state->coerceToStorePath(outPath->pos, *outPath->value, context));
                 } else
                     outputs.emplace(output, std::nullopt);
             }
@@ -168,7 +168,7 @@ Bindings * DrvInfo::getMeta()
     if (!attrs) return 0;
     Bindings::iterator a = attrs->find(state->sMeta);
     if (a == attrs->end()) return 0;
-    state->forceAttrs(*a->value, *a->pos);
+    state->forceAttrs(*a->value, a->pos);
     meta = a->value->attrs;
     return meta;
 }
@@ -179,7 +179,7 @@ StringSet DrvInfo::queryMetaNames()
     StringSet res;
     if (!getMeta()) return res;
     for (auto & i : *meta)
-        res.insert(i.name);
+        res.emplace(state->symbols[i.name]);
     return res;
 }
 
@@ -269,7 +269,7 @@ void DrvInfo::setMeta(const std::string & name, Value * v)
 {
     getMeta();
     auto attrs = state->buildBindings(1 + (meta ? meta->size() : 0));
-    Symbol sym = state->symbols.create(name);
+    auto sym = state->symbols.create(name);
     if (meta)
         for (auto i : *meta)
             if (i.name != sym)
@@ -356,11 +356,11 @@ static void getDerivations(EvalState & state, Value & vIn,
            there are names clashes between derivations, the derivation
            bound to the attribute with the "lower" name should take
            precedence). */
-        for (auto & i : v.attrs->lexicographicOrder()) {
+        for (auto & i : v.attrs->lexicographicOrder(state.symbols)) {
-            debug("evaluating attribute '%1%'", i->name);
+            debug("evaluating attribute '%1%'", state.symbols[i->name]);
-            if (!std::regex_match(std::string(i->name), attrRegex))
+            if (!std::regex_match(std::string(state.symbols[i->name]), attrRegex))
                 continue;
-            std::string pathPrefix2 = addToPath(pathPrefix, i->name);
+            std::string pathPrefix2 = addToPath(pathPrefix, state.symbols[i->name]);
             if (combineChannels)
                 getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
             else if (getDerivation(state, *i->value, pathPrefix2, drvs, done, ignoreAssertionFailures)) {
@@ -369,7 +369,7 @@ static void getDerivations(EvalState & state, Value & vIn,
                    `recurseForDerivations = true' attribute. */
                 if (i->value->type() == nAttrs) {
                     Bindings::iterator j = i->value->attrs->find(state.sRecurseForDerivations);
-                    if (j != i->value->attrs->end() && state.forceBool(*j->value, *j->pos))
+                    if (j != i->value->attrs->end() && state.forceBool(*j->value, j->pos))
                         getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
                 }
             }

src/libexpr/lexer.l

@@ -28,9 +28,9 @@ using namespace nix;
 
 namespace nix {
 
-static inline Pos makeCurPos(const YYLTYPE & loc, ParseData * data)
+static inline PosIdx makeCurPos(const YYLTYPE & loc, ParseData * data)
 {
-    return Pos(data->origin, data->file, loc.first_line, loc.first_column);
+    return data->state.positions.add(data->origin, loc.first_line, loc.first_column);
 }
 
 #define CUR_POS makeCurPos(*yylloc, data)
@@ -155,7 +155,7 @@ or          { return OR_KW; }
               } catch (const boost::bad_lexical_cast &) {
                   throw ParseError({
                       .msg = hintfmt("invalid integer '%1%'", yytext),
-                      .errPos = CUR_POS,
+                      .errPos = data->state.positions[CUR_POS],
                   });
               }
               return INT;
@@ -165,7 +165,7 @@ or          { return OR_KW; }
               if (errno != 0)
                   throw ParseError({
                       .msg = hintfmt("invalid float '%1%'", yytext),
-                      .errPos = CUR_POS,
+                      .errPos = data->state.positions[CUR_POS],
                   });
               return FLOAT;
             }
@@ -294,7 +294,7 @@ or          { return OR_KW; }
 <INPATH_SLASH><<EOF>> {
   throw ParseError({
       .msg = hintfmt("path has a trailing slash"),
-      .errPos = CUR_POS,
+      .errPos = data->state.positions[CUR_POS],
   });
 }
 

src/libexpr/nixexpr.cc

@@ -1,5 +1,7 @@
 #include "nixexpr.hh"
 #include "derivations.hh"
+#include "eval.hh"
+#include "symbol-table.hh"
 #include "util.hh"
 
 #include <cstdlib>
@@ -10,12 +12,6 @@ namespace nix {
 
 /* Displaying abstract syntax trees. */
 
-std::ostream & operator << (std::ostream & str, const Expr & e)
-{
-    e.show(str);
-    return str;
-}
-
 static void showString(std::ostream & str, std::string_view s)
 {
     str << '"';
@@ -54,81 +50,101 @@ static void showId(std::ostream & str, std::string_view s)
 
 std::ostream & operator << (std::ostream & str, const Symbol & sym)
 {
-    showId(str, *sym.s);
+    showId(str, sym.s);
     return str;
 }
 
-void Expr::show(std::ostream & str) const
+void Expr::show(const SymbolTable & symbols, std::ostream & str) const
 {
     abort();
 }
 
-void ExprInt::show(std::ostream & str) const
+void ExprInt::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << n;
 }
 
-void ExprFloat::show(std::ostream & str) const
+void ExprFloat::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << nf;
 }
 
-void ExprString::show(std::ostream & str) const
+void ExprString::show(const SymbolTable & symbols, std::ostream & str) const
 {
     showString(str, s);
 }
 
-void ExprPath::show(std::ostream & str) const
+void ExprPath::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << s;
 }
 
-void ExprVar::show(std::ostream & str) const
+void ExprVar::show(const SymbolTable & symbols, std::ostream & str) const
 {
-    str << name;
+    str << symbols[name];
 }
 
-void ExprSelect::show(std::ostream & str) const
+void ExprSelect::show(const SymbolTable & symbols, std::ostream & str) const
 {
-    str << "(" << *e << ")." << showAttrPath(attrPath);
+    str << "(";
-    if (def) str << " or (" << *def << ")";
+    e->show(symbols, str);
+    str << ")." << showAttrPath(symbols, attrPath);
+    if (def) {
+        str << " or (";
+        def->show(symbols, str);
+        str << ")";
+    }
 }
 
-void ExprOpHasAttr::show(std::ostream & str) const
+void ExprOpHasAttr::show(const SymbolTable & symbols, std::ostream & str) const
 {
-    str << "((" << *e << ") ? " << showAttrPath(attrPath) << ")";
+    str << "((";
+    e->show(symbols, str);
+    str << ") ? " << showAttrPath(symbols, attrPath) << ")";
 }
 
-void ExprAttrs::show(std::ostream & str) const
+void ExprAttrs::show(const SymbolTable & symbols, std::ostream & str) const
 {
     if (recursive) str << "rec ";
     str << "{ ";
     typedef const decltype(attrs)::value_type * Attr;
     std::vector<Attr> sorted;
     for (auto & i : attrs) sorted.push_back(&i);
-        std::sort(sorted.begin(), sorted.end(), [](Attr a, Attr b) {
+    std::sort(sorted.begin(), sorted.end(), [&](Attr a, Attr b) {
-            return (const std::string &) a->first < (const std::string &) b->first;
+        std::string_view sa = symbols[a->first], sb = symbols[b->first];
-        });
+        return sa < sb;
+    });
     for (auto & i : sorted) {
         if (i->second.inherited)
-            str << "inherit " << i->first << " " << "; ";
+            str << "inherit " << symbols[i->first] << " " << "; ";
-        else
+        else {
-            str << i->first << " = " << *i->second.e << "; ";
+            str << symbols[i->first] << " = ";
+            i->second.e->show(symbols, str);
+            str << "; ";
+        }
+    }
+    for (auto & i : dynamicAttrs) {
+        str << "\"${";
+        i.nameExpr->show(symbols, str);
+        str << "}\" = ";
+        i.valueExpr->show(symbols, str);
+        str << "; ";
     }
-    for (auto & i : dynamicAttrs)
-        str << "\"${" << *i.nameExpr << "}\" = " << *i.valueExpr << "; ";
     str << "}";
 }
 
-void ExprList::show(std::ostream & str) const
+void ExprList::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "[ ";
-    for (auto & i : elems)
+    for (auto & i : elems) {
-        str << "(" << *i << ") ";
+        str << "(";
+        i->show(symbols, str);
+        str << ") ";
+    }
     str << "]";
 }
 
-void ExprLambda::show(std::ostream & str) const
+void ExprLambda::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "(";
     if (hasFormals()) {
@@ -136,74 +152,100 @@ void ExprLambda::show(std::ostream & str) const
         bool first = true;
         for (auto & i : formals->formals) {
             if (first) first = false; else str << ", ";
-            str << i.name;
+            str << symbols[i.name];
-            if (i.def) str << " ? " << *i.def;
+            if (i.def) {
+                str << " ? ";
+                i.def->show(symbols, str);
+            }
         }
         if (formals->ellipsis) {
             if (!first) str << ", ";
             str << "...";
         }
         str << " }";
-        if (!arg.empty()) str << " @ ";
+        if (arg) str << " @ ";
     }
-    if (!arg.empty()) str << arg;
+    if (arg) str << symbols[arg];
-    str << ": " << *body << ")";
+    str << ": ";
+    body->show(symbols, str);
+    str << ")";
 }
 
-void ExprCall::show(std::ostream & str) const
+void ExprCall::show(const SymbolTable & symbols, std::ostream & str) const
 {
-    str << '(' << *fun;
+    str << '(';
+    fun->show(symbols, str);
     for (auto e : args) {
         str <<  ' ';
-        str << *e;
+        e->show(symbols, str);
     }
     str << ')';
 }
 
-void ExprLet::show(std::ostream & str) const
+void ExprLet::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "(let ";
     for (auto & i : attrs->attrs)
         if (i.second.inherited) {
-            str << "inherit " << i.first << "; ";
+            str << "inherit " << symbols[i.first] << "; ";
         }
-        else
+        else {
-            str << i.first << " = " << *i.second.e << "; ";
+            str << symbols[i.first] << " = ";
-    str << "in " << *body << ")";
+            i.second.e->show(symbols, str);
+            str << "; ";
+        }
+    str << "in ";
+    body->show(symbols, str);
+    str << ")";
 }
 
-void ExprWith::show(std::ostream & str) const
+void ExprWith::show(const SymbolTable & symbols, std::ostream & str) const
 {
-    str << "(with " << *attrs << "; " << *body << ")";
+    str << "(with ";
+    attrs->show(symbols, str);
+    str << "; ";
+    body->show(symbols, str);
+    str << ")";
 }
 
-void ExprIf::show(std::ostream & str) const
+void ExprIf::show(const SymbolTable & symbols, std::ostream & str) const
 {
-    str << "(if " << *cond << " then " << *then << " else " << *else_ << ")";
+    str << "(if ";
+    cond->show(symbols, str);
+    str << " then ";
+    then->show(symbols, str);
+    str << " else ";
+    else_->show(symbols, str);
+    str << ")";
 }
 
-void ExprAssert::show(std::ostream & str) const
+void ExprAssert::show(const SymbolTable & symbols, std::ostream & str) const
 {
-    str << "assert " << *cond << "; " << *body;
+    str << "assert ";
+    cond->show(symbols, str);
+    str << "; ";
+    body->show(symbols, str);
 }
 
-void ExprOpNot::show(std::ostream & str) const
+void ExprOpNot::show(const SymbolTable & symbols, std::ostream & str) const
 {
-    str << "(! " << *e << ")";
+    str << "(! ";
+    e->show(symbols, str);
+    str << ")";
 }
 
-void ExprConcatStrings::show(std::ostream & str) const
+void ExprConcatStrings::show(const SymbolTable & symbols, std::ostream & str) const
 {
     bool first = true;
     str << "(";
     for (auto & i : *es) {
         if (first) first = false; else str << " + ";
-        str << *i.second;
+        i.second->show(symbols, str);
     }
     str << ")";
 }
 
-void ExprPos::show(std::ostream & str) const
+void ExprPos::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "__curPos";
 }
@@ -234,48 +276,49 @@ std::ostream & operator << (std::ostream & str, const Pos & pos)
 }
 
 
-std::string showAttrPath(const AttrPath & attrPath)
+std::string showAttrPath(const SymbolTable & symbols, const AttrPath & attrPath)
 {
     std::ostringstream out;
     bool first = true;
     for (auto & i : attrPath) {
         if (!first) out << '.'; else first = false;
-        if (i.symbol.set())
+        if (i.symbol)
-            out << i.symbol;
+            out << symbols[i.symbol];
-        else
+        else {
-            out << "\"${" << *i.expr << "}\"";
+            out << "\"${";
+            i.expr->show(symbols, out);
+            out << "}\"";
+        }
     }
     return out.str();
 }
 
 
-Pos noPos;
-
 
 /* Computing levels/displacements for variables. */
 
-void Expr::bindVars(const StaticEnv & env)
+void Expr::bindVars(const EvalState & es, const StaticEnv & env)
 {
     abort();
 }
 
-void ExprInt::bindVars(const StaticEnv & env)
+void ExprInt::bindVars(const EvalState & es, const StaticEnv & env)
 {
 }
 
-void ExprFloat::bindVars(const StaticEnv & env)
+void ExprFloat::bindVars(const EvalState & es, const StaticEnv & env)
 {
 }
 
-void ExprString::bindVars(const StaticEnv & env)
+void ExprString::bindVars(const EvalState & es, const StaticEnv & env)
 {
 }
 
-void ExprPath::bindVars(const StaticEnv & env)
+void ExprPath::bindVars(const EvalState & es, const StaticEnv & env)
 {
 }
 
-void ExprVar::bindVars(const StaticEnv & env)
+void ExprVar::bindVars(const EvalState & es, const StaticEnv & env)
 {
     /* Check whether the variable appears in the environment.  If so,
        set its level and displacement. */
@@ -301,31 +344,31 @@ void ExprVar::bindVars(const StaticEnv & env)
        "undefined variable" error now. */
     if (withLevel == -1)
         throw UndefinedVarError({
-            .msg = hintfmt("undefined variable '%1%'", name),
+            .msg = hintfmt("undefined variable '%1%'", es.symbols[name]),
-            .errPos = pos
+            .errPos = es.positions[pos]
         });
     fromWith = true;
     this->level = withLevel;
 }
 
-void ExprSelect::bindVars(const StaticEnv & env)
+void ExprSelect::bindVars(const EvalState & es, const StaticEnv & env)
 {
-    e->bindVars(env);
+    e->bindVars(es, env);
-    if (def) def->bindVars(env);
+    if (def) def->bindVars(es, env);
     for (auto & i : attrPath)
-        if (!i.symbol.set())
+        if (!i.symbol)
-            i.expr->bindVars(env);
+            i.expr->bindVars(es, env);
 }
 
-void ExprOpHasAttr::bindVars(const StaticEnv & env)
+void ExprOpHasAttr::bindVars(const EvalState & es, const StaticEnv & env)
 {
-    e->bindVars(env);
+    e->bindVars(es, env);
     for (auto & i : attrPath)
-        if (!i.symbol.set())
+        if (!i.symbol)
-            i.expr->bindVars(env);
+            i.expr->bindVars(es, env);
 }
 
-void ExprAttrs::bindVars(const StaticEnv & env)
+void ExprAttrs::bindVars(const EvalState & es, const StaticEnv & env)
 {
     const StaticEnv * dynamicEnv = &env;
     StaticEnv newEnv(false, &env, recursive ? attrs.size() : 0);
@@ -340,35 +383,35 @@ void ExprAttrs::bindVars(const StaticEnv & env)
         // No need to sort newEnv since attrs is in sorted order.
 
         for (auto & i : attrs)
-            i.second.e->bindVars(i.second.inherited ? env : newEnv);
+            i.second.e->bindVars(es, i.second.inherited ? env : newEnv);
     }
 
     else
         for (auto & i : attrs)
-            i.second.e->bindVars(env);
+            i.second.e->bindVars(es, env);
 
     for (auto & i : dynamicAttrs) {
-        i.nameExpr->bindVars(*dynamicEnv);
+        i.nameExpr->bindVars(es, *dynamicEnv);
-        i.valueExpr->bindVars(*dynamicEnv);
+        i.valueExpr->bindVars(es, *dynamicEnv);
     }
 }
 
-void ExprList::bindVars(const StaticEnv & env)
+void ExprList::bindVars(const EvalState & es, const StaticEnv & env)
 {
     for (auto & i : elems)
-        i->bindVars(env);
+        i->bindVars(es, env);
 }
 
-void ExprLambda::bindVars(const StaticEnv & env)
+void ExprLambda::bindVars(const EvalState & es, const StaticEnv & env)
 {
     StaticEnv newEnv(
         false, &env,
         (hasFormals() ? formals->formals.size() : 0) +
-        (arg.empty() ? 0 : 1));
+        (!arg ? 0 : 1));
 
     Displacement displ = 0;
 
-    if (!arg.empty()) newEnv.vars.emplace_back(arg, displ++);
+    if (arg) newEnv.vars.emplace_back(arg, displ++);
 
     if (hasFormals()) {
         for (auto & i : formals->formals)
@@ -377,20 +420,20 @@ void ExprLambda::bindVars(const StaticEnv & env)
         newEnv.sort();
 
         for (auto & i : formals->formals)
-            if (i.def) i.def->bindVars(newEnv);
+            if (i.def) i.def->bindVars(es, newEnv);
     }
 
-    body->bindVars(newEnv);
+    body->bindVars(es, newEnv);
 }
 
-void ExprCall::bindVars(const StaticEnv & env)
+void ExprCall::bindVars(const EvalState & es, const StaticEnv & env)
 {
-    fun->bindVars(env);
+    fun->bindVars(es, env);
     for (auto e : args)
-        e->bindVars(env);
+        e->bindVars(es, env);
 }
 
-void ExprLet::bindVars(const StaticEnv & env)
+void ExprLet::bindVars(const EvalState & es, const StaticEnv & env)
 {
     StaticEnv newEnv(false, &env, attrs->attrs.size());
 
@@ -401,12 +444,12 @@ void ExprLet::bindVars(const StaticEnv & env)
     // No need to sort newEnv since attrs->attrs is in sorted order.
 
     for (auto & i : attrs->attrs)
-        i.second.e->bindVars(i.second.inherited ? env : newEnv);
+        i.second.e->bindVars(es, i.second.inherited ? env : newEnv);
 
-    body->bindVars(newEnv);
+    body->bindVars(es, newEnv);
 }
 
-void ExprWith::bindVars(const StaticEnv & env)
+void ExprWith::bindVars(const EvalState & es, const StaticEnv & env)
 {
     /* Does this `with' have an enclosing `with'?  If so, record its
        level so that `lookupVar' can look up variables in the previous
@@ -420,57 +463,60 @@ void ExprWith::bindVars(const StaticEnv & env)
             break;
         }
 
-    attrs->bindVars(env);
+    attrs->bindVars(es, env);
     StaticEnv newEnv(true, &env);
-    body->bindVars(newEnv);
+    body->bindVars(es, newEnv);
 }
 
-void ExprIf::bindVars(const StaticEnv & env)
+void ExprIf::bindVars(const EvalState & es, const StaticEnv & env)
 {
-    cond->bindVars(env);
+    cond->bindVars(es, env);
-    then->bindVars(env);
+    then->bindVars(es, env);
-    else_->bindVars(env);
+    else_->bindVars(es, env);
 }
 
-void ExprAssert::bindVars(const StaticEnv & env)
+void ExprAssert::bindVars(const EvalState & es, const StaticEnv & env)
 {
-    cond->bindVars(env);
+    cond->bindVars(es, env);
-    body->bindVars(env);
+    body->bindVars(es, env);
 }
 
-void ExprOpNot::bindVars(const StaticEnv & env)
+void ExprOpNot::bindVars(const EvalState & es, const StaticEnv & env)
 {
-    e->bindVars(env);
+    e->bindVars(es, env);
 }
 
-void ExprConcatStrings::bindVars(const StaticEnv & env)
+void ExprConcatStrings::bindVars(const EvalState & es, const StaticEnv & env)
 {
-    for (auto & i : *es)
+    for (auto & i : *this->es)
-        i.second->bindVars(env);
+        i.second->bindVars(es, env);
 }
 
-void ExprPos::bindVars(const StaticEnv & env)
+void ExprPos::bindVars(const EvalState & es, const StaticEnv & env)
 {
 }
 
 
 /* Storing function names. */
 
-void Expr::setName(Symbol & name)
+void Expr::setName(SymbolIdx name)
 {
 }
 
 
-void ExprLambda::setName(Symbol & name)
+void ExprLambda::setName(SymbolIdx name)
 {
     this->name = name;
     body->setName(name);
 }
 
 
-std::string ExprLambda::showNamePos() const
+std::string ExprLambda::showNamePos(const EvalState & state) const
 {
-    return fmt("%1% at %2%", name.set() ? "'" + (std::string) name + "'" : "anonymous function", pos);
+    std::string id(name
+        ? concatStrings("'", state.symbols[name], "'")
+        : "anonymous function");
+    return fmt("%1% at %2%", id, state.positions[pos]);
 }
 
 
@@ -480,8 +526,7 @@ std::string ExprLambda::showNamePos() const
 size_t SymbolTable::totalSize() const
 {
     size_t n = 0;
-    for (auto & i : store)
+    dump([&] (const Symbol & s) { n += std::string_view(s).size(); });
-        n += i.size();
     return n;
 }
 

src/libexpr/nixexpr.hh

@@ -1,8 +1,12 @@
 #pragma once
 
+#include <map>
+#include <vector>
+
 #include "value.hh"
 #include "symbol-table.hh"
 #include "error.hh"
+#include "chunked-vector.hh"
 
 
 namespace nix {
@@ -23,32 +27,92 @@ MakeError(RestrictedPathError, Error);
 
 struct Pos
 {
-    Symbol file;
+    std::string file;
+    FileOrigin origin;
     uint32_t line;
-    FileOrigin origin:2;
+    uint32_t column;
-    uint32_t column:30;
+
-    Pos() : line(0), origin(foString), column(0) { };
+    explicit operator bool() const { return line > 0; }
-    Pos(FileOrigin origin, const Symbol & file, uint32_t line, uint32_t column)
+};
-        : file(file), line(line), origin(origin), column(column) { };
+
-    operator bool() const
+class PosIdx {
+    friend class PosTable;
+
+private:
+    uint32_t id;
+
+    explicit PosIdx(uint32_t id): id(id) {}
+
+public:
+    PosIdx() : id(0) {}
+
+    explicit operator bool() const { return id > 0; }
+
+    bool operator<(const PosIdx other) const { return id < other.id; }
+};
+
+class PosTable
+{
+public:
+    class Origin {
+        friend PosTable;
+    private:
+        // must always be invalid by default, add() replaces this with the actual value.
+        // subsequent add() calls use this index as a token to quickly check whether the
+        // current origins.back() can be reused or not.
+        mutable uint32_t idx = std::numeric_limits<uint32_t>::max();
+
+        explicit Origin(uint32_t idx): idx(idx), file{}, origin{} {}
+
+    public:
+        const std::string file;
+        const FileOrigin origin;
+
+        Origin(std::string file, FileOrigin origin): file(std::move(file)), origin(origin) {}
+    };
+
+    struct Offset {
+        uint32_t line, column;
+    };
+
+private:
+    std::vector<Origin> origins;
+    ChunkedVector<Offset, 8192> offsets;
+
+public:
+    PosTable(): offsets(1024)
     {
-        return line != 0;
+        origins.reserve(1024);
     }
 
-    bool operator < (const Pos & p2) const
+    PosIdx add(const Origin & origin, uint32_t line, uint32_t column)
     {
-        if (!line) return p2.line;
+        const auto idx = offsets.add({line, column}).second;
-        if (!p2.line) return false;
+        if (origins.empty() || origins.back().idx != origin.idx) {
-        int d = ((const std::string &) file).compare((const std::string &) p2.file);
+            origin.idx = idx;
-        if (d < 0) return true;
+            origins.push_back(origin);
-        if (d > 0) return false;
+        }
-        if (line < p2.line) return true;
+        return PosIdx(idx + 1);
-        if (line > p2.line) return false;
+    }
-        return column < p2.column;
+
+    Pos operator[](PosIdx p) const
+    {
+        if (p.id == 0 || p.id > offsets.size())
+            return {};
+        const auto idx = p.id - 1;
+        /* we want the last key <= idx, so we'll take prev(first key > idx).
+           this is guaranteed to never rewind origin.begin because the first
+           key is always 0. */
+        const auto pastOrigin = std::upper_bound(
+            origins.begin(), origins.end(), Origin(idx),
+            [] (const auto & a, const auto & b) { return a.idx < b.idx; });
+        const auto origin = *std::prev(pastOrigin);
+        const auto offset = offsets[idx];
+        return {origin.file, origin.origin, offset.line, offset.column};
     }
 };
 
-extern Pos noPos;
+inline PosIdx noPos = {};
 
 std::ostream & operator << (std::ostream & str, const Pos & pos);
 
@@ -62,15 +126,15 @@ struct StaticEnv;
 /* An attribute path is a sequence of attribute names. */
 struct AttrName
 {
-    Symbol symbol;
+    SymbolIdx symbol;
     Expr * expr;
-    AttrName(const Symbol & s) : symbol(s) {};
+    AttrName(const SymbolIdx & s) : symbol(s) {};
     AttrName(Expr * e) : expr(e) {};
 };
 
 typedef std::vector<AttrName> AttrPath;
 
-std::string showAttrPath(const AttrPath & attrPath);
+std::string showAttrPath(const SymbolTable & symbols, const AttrPath & attrPath);
 
 
 /* Abstract syntax of Nix expressions. */
@@ -78,19 +142,17 @@ std::string showAttrPath(const AttrPath & attrPath);
 struct Expr
 {
     virtual ~Expr() { };
-    virtual void show(std::ostream & str) const;
+    virtual void show(const SymbolTable & symbols, std::ostream & str) const;
-    virtual void bindVars(const StaticEnv & env);
+    virtual void bindVars(const EvalState & es, const StaticEnv & env);
     virtual void eval(EvalState & state, Env & env, Value & v);
     virtual Value * maybeThunk(EvalState & state, Env & env);
-    virtual void setName(Symbol & name);
+    virtual void setName(SymbolIdx name);
 };
 
-std::ostream & operator << (std::ostream & str, const Expr & e);
-
 #define COMMON_METHODS \
-    void show(std::ostream & str) const; \
+    void show(const SymbolTable & symbols, std::ostream & str) const;    \
     void eval(EvalState & state, Env & env, Value & v); \
-    void bindVars(const StaticEnv & env);
+    void bindVars(const EvalState & es, const StaticEnv & env);
 
 struct ExprInt : Expr
 {
@@ -133,8 +195,8 @@ typedef uint32_t Displacement;
 
 struct ExprVar : Expr
 {
-    Pos pos;
+    PosIdx pos;
-    Symbol name;
+    SymbolIdx name;
 
     /* Whether the variable comes from an environment (e.g. a rec, let
        or function argument) or from a "with". */
@@ -149,19 +211,19 @@ struct ExprVar : Expr
     Level level;
     Displacement displ;
 
-    ExprVar(const Symbol & name) : name(name) { };
+    ExprVar(const SymbolIdx & name) : name(name) { };
-    ExprVar(const Pos & pos, const Symbol & name) : pos(pos), name(name) { };
+    ExprVar(const PosIdx & pos, const SymbolIdx & name) : pos(pos), name(name) { };
     COMMON_METHODS
     Value * maybeThunk(EvalState & state, Env & env);
 };
 
 struct ExprSelect : Expr
 {
-    Pos pos;
+    PosIdx pos;
     Expr * e, * def;
     AttrPath attrPath;
-    ExprSelect(const Pos & pos, Expr * e, const AttrPath & attrPath, Expr * def) : pos(pos), e(e), def(def), attrPath(attrPath) { };
+    ExprSelect(const PosIdx & pos, Expr * e, const AttrPath & attrPath, Expr * def) : pos(pos), e(e), def(def), attrPath(attrPath) { };
-    ExprSelect(const Pos & pos, Expr * e, const Symbol & name) : pos(pos), e(e), def(0) { attrPath.push_back(AttrName(name)); };
+    ExprSelect(const PosIdx & pos, Expr * e, const SymbolIdx & name) : pos(pos), e(e), def(0) { attrPath.push_back(AttrName(name)); };
     COMMON_METHODS
 };
 
@@ -176,28 +238,28 @@ struct ExprOpHasAttr : Expr
 struct ExprAttrs : Expr
 {
     bool recursive;
-    Pos pos;
+    PosIdx pos;
     struct AttrDef {
         bool inherited;
         Expr * e;
-        Pos pos;
+        PosIdx pos;
         Displacement displ; // displacement
-        AttrDef(Expr * e, const Pos & pos, bool inherited=false)
+        AttrDef(Expr * e, const PosIdx & pos, bool inherited=false)
             : inherited(inherited), e(e), pos(pos) { };
         AttrDef() { };
     };
-    typedef std::map<Symbol, AttrDef> AttrDefs;
+    typedef std::map<SymbolIdx, AttrDef> AttrDefs;
     AttrDefs attrs;
     struct DynamicAttrDef {
         Expr * nameExpr, * valueExpr;
-        Pos pos;
+        PosIdx pos;
-        DynamicAttrDef(Expr * nameExpr, Expr * valueExpr, const Pos & pos)
+        DynamicAttrDef(Expr * nameExpr, Expr * valueExpr, const PosIdx & pos)
             : nameExpr(nameExpr), valueExpr(valueExpr), pos(pos) { };
     };
     typedef std::vector<DynamicAttrDef> DynamicAttrDefs;
     DynamicAttrDefs dynamicAttrs;
-    ExprAttrs(const Pos &pos) : recursive(false), pos(pos) { };
+    ExprAttrs(const PosIdx &pos) : recursive(false), pos(pos) { };
-    ExprAttrs() : recursive(false), pos(noPos) { };
+    ExprAttrs() : recursive(false) { };
     COMMON_METHODS
 };
 
@@ -210,10 +272,9 @@ struct ExprList : Expr
 
 struct Formal
 {
-    Pos pos;
+    PosIdx pos;
-    Symbol name;
+    SymbolIdx name;
     Expr * def;
-    Formal(const Pos & pos, const Symbol & name, Expr * def) : pos(pos), name(name), def(def) { };
 };
 
 struct Formals
@@ -222,18 +283,19 @@ struct Formals
     Formals_ formals;
     bool ellipsis;
 
-    bool has(Symbol arg) const {
+    bool has(SymbolIdx arg) const {
         auto it = std::lower_bound(formals.begin(), formals.end(), arg,
-            [] (const Formal & f, const Symbol & sym) { return f.name < sym; });
+            [] (const Formal & f, const SymbolIdx & sym) { return f.name < sym; });
         return it != formals.end() && it->name == arg;
     }
 
-    std::vector<Formal> lexicographicOrder() const
+    std::vector<Formal> lexicographicOrder(const SymbolTable & symbols) const
     {
         std::vector<Formal> result(formals.begin(), formals.end());
         std::sort(result.begin(), result.end(),
-            [] (const Formal & a, const Formal & b) {
+            [&] (const Formal & a, const Formal & b) {
-                return std::string_view(a.name) < std::string_view(b.name);
+                std::string_view sa = symbols[a.name], sb = symbols[b.name];
+                return sa < sb;
             });
         return result;
     }
@@ -241,17 +303,21 @@ struct Formals
 
 struct ExprLambda : Expr
 {
-    Pos pos;
+    PosIdx pos;
-    Symbol name;
+    SymbolIdx name;
-    Symbol arg;
+    SymbolIdx arg;
     Formals * formals;
     Expr * body;
-    ExprLambda(const Pos & pos, const Symbol & arg, Formals * formals, Expr * body)
+    ExprLambda(PosIdx pos, SymbolIdx arg, Formals * formals, Expr * body)
         : pos(pos), arg(arg), formals(formals), body(body)
     {
     };
-    void setName(Symbol & name);
+    ExprLambda(PosIdx pos, Formals * formals, Expr * body)
-    std::string showNamePos() const;
+        : pos(pos), formals(formals), body(body)
+    {
+    }
+    void setName(SymbolIdx name);
+    std::string showNamePos(const EvalState & state) const;
     inline bool hasFormals() const { return formals != nullptr; }
     COMMON_METHODS
 };
@@ -260,8 +326,8 @@ struct ExprCall : Expr
 {
     Expr * fun;
     std::vector<Expr *> args;
-    Pos pos;
+    PosIdx pos;
-    ExprCall(const Pos & pos, Expr * fun, std::vector<Expr *> && args)
+    ExprCall(const PosIdx & pos, Expr * fun, std::vector<Expr *> && args)
         : fun(fun), args(args), pos(pos)
     { }
     COMMON_METHODS
@@ -277,26 +343,26 @@ struct ExprLet : Expr
 
 struct ExprWith : Expr
 {
-    Pos pos;
+    PosIdx pos;
     Expr * attrs, * body;
     size_t prevWith;
-    ExprWith(const Pos & pos, Expr * attrs, Expr * body) : pos(pos), attrs(attrs), body(body) { };
+    ExprWith(const PosIdx & pos, Expr * attrs, Expr * body) : pos(pos), attrs(attrs), body(body) { };
     COMMON_METHODS
 };
 
 struct ExprIf : Expr
 {
-    Pos pos;
+    PosIdx pos;
     Expr * cond, * then, * else_;
-    ExprIf(const Pos & pos, Expr * cond, Expr * then, Expr * else_) : pos(pos), cond(cond), then(then), else_(else_) { };
+    ExprIf(const PosIdx & pos, Expr * cond, Expr * then, Expr * else_) : pos(pos), cond(cond), then(then), else_(else_) { };
     COMMON_METHODS
 };
 
 struct ExprAssert : Expr
 {
-    Pos pos;
+    PosIdx pos;
     Expr * cond, * body;
-    ExprAssert(const Pos & pos, Expr * cond, Expr * body) : pos(pos), cond(cond), body(body) { };
+    ExprAssert(const PosIdx & pos, Expr * cond, Expr * body) : pos(pos), cond(cond), body(body) { };
     COMMON_METHODS
 };
 
@@ -310,17 +376,17 @@ struct ExprOpNot : Expr
 #define MakeBinOp(name, s) \
     struct name : Expr \
     { \
-        Pos pos; \
+        PosIdx pos; \
         Expr * e1, * e2; \
         name(Expr * e1, Expr * e2) : e1(e1), e2(e2) { }; \
-        name(const Pos & pos, Expr * e1, Expr * e2) : pos(pos), e1(e1), e2(e2) { }; \
+        name(const PosIdx & pos, Expr * e1, Expr * e2) : pos(pos), e1(e1), e2(e2) { }; \
-        void show(std::ostream & str) const \
+        void show(const SymbolTable & symbols, std::ostream & str) const \
         { \
-            str << "(" << *e1 << " " s " " << *e2 << ")";   \
+            str << "("; e1->show(symbols, str); str << " " s " "; e2->show(symbols, str); str << ")"; \
         } \
-        void bindVars(const StaticEnv & env) \
+        void bindVars(const EvalState & es, const StaticEnv & env)    \
         { \
-            e1->bindVars(env); e2->bindVars(env); \
+            e1->bindVars(es, env); e2->bindVars(es, env);    \
         } \
         void eval(EvalState & state, Env & env, Value & v); \
     };
@@ -335,18 +401,18 @@ MakeBinOp(ExprOpConcatLists, "++")
 
 struct ExprConcatStrings : Expr
 {
-    Pos pos;
+    PosIdx pos;
     bool forceString;
-    std::vector<std::pair<Pos, Expr *> > * es;
+    std::vector<std::pair<PosIdx, Expr *> > * es;
-    ExprConcatStrings(const Pos & pos, bool forceString, std::vector<std::pair<Pos, Expr *> > * es)
+    ExprConcatStrings(const PosIdx & pos, bool forceString, std::vector<std::pair<PosIdx, Expr *> > * es)
         : pos(pos), forceString(forceString), es(es) { };
     COMMON_METHODS
 };
 
 struct ExprPos : Expr
 {
-    Pos pos;
+    PosIdx pos;
-    ExprPos(const Pos & pos) : pos(pos) { };
+    ExprPos(const PosIdx & pos) : pos(pos) { };
     COMMON_METHODS
 };
 
@@ -360,7 +426,7 @@ struct StaticEnv
     const StaticEnv * up;
 
     // Note: these must be in sorted order.
-    typedef std::vector<std::pair<Symbol, Displacement>> Vars;
+    typedef std::vector<std::pair<SymbolIdx, Displacement>> Vars;
     Vars vars;
 
     StaticEnv(bool isWith, const StaticEnv * up, size_t expectedSize = 0) : isWith(isWith), up(up) {
@@ -384,7 +450,7 @@ struct StaticEnv
         vars.erase(it, end);
     }
 
-    Vars::const_iterator find(const Symbol & name) const
+    Vars::const_iterator find(const SymbolIdx & name) const
     {
         Vars::value_type key(name, 0);
         auto i = std::lower_bound(vars.begin(), vars.end(), key);

src/libexpr/parser.y

@@ -32,12 +32,12 @@ namespace nix {
         SymbolTable & symbols;
         Expr * result;
         Path basePath;
-        Symbol file;
+        PosTable::Origin origin;
-        FileOrigin origin;
         std::optional<ErrorInfo> error;
-        ParseData(EvalState & state)
+        ParseData(EvalState & state, PosTable::Origin origin)
             : state(state)
             , symbols(state.symbols)
+            , origin(std::move(origin))
             { };
     };
 
@@ -77,26 +77,26 @@ using namespace nix;
 namespace nix {
 
 
-static void dupAttr(const AttrPath & attrPath, const Pos & pos, const Pos & prevPos)
+static void dupAttr(const EvalState & state, const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos)
 {
     throw ParseError({
          .msg = hintfmt("attribute '%1%' already defined at %2%",
-             showAttrPath(attrPath), prevPos),
+             showAttrPath(state.symbols, attrPath), state.positions[prevPos]),
-         .errPos = pos
+         .errPos = state.positions[pos]
     });
 }
 
-static void dupAttr(Symbol attr, const Pos & pos, const Pos & prevPos)
+static void dupAttr(const EvalState & state, SymbolIdx attr, const PosIdx pos, const PosIdx prevPos)
 {
     throw ParseError({
-        .msg = hintfmt("attribute '%1%' already defined at %2%", attr, prevPos),
+        .msg = hintfmt("attribute '%1%' already defined at %2%", state.symbols[attr], state.positions[prevPos]),
-        .errPos = pos
+        .errPos = state.positions[pos]
     });
 }
 
 
 static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
-    Expr * e, const Pos & pos)
+    Expr * e, const PosIdx pos, const nix::EvalState & state)
 {
     AttrPath::iterator i;
     // All attrpaths have at least one attr
@@ -104,15 +104,15 @@ static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
     // Checking attrPath validity.
     // ===========================
     for (i = attrPath.begin(); i + 1 < attrPath.end(); i++) {
-        if (i->symbol.set()) {
+        if (i->symbol) {
             ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
             if (j != attrs->attrs.end()) {
                 if (!j->second.inherited) {
                     ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.e);
-                    if (!attrs2) dupAttr(attrPath, pos, j->second.pos);
+                    if (!attrs2) dupAttr(state, attrPath, pos, j->second.pos);
                     attrs = attrs2;
                 } else
-                    dupAttr(attrPath, pos, j->second.pos);
+                    dupAttr(state, attrPath, pos, j->second.pos);
             } else {
                 ExprAttrs * nested = new ExprAttrs;
                 attrs->attrs[i->symbol] = ExprAttrs::AttrDef(nested, pos);
@@ -126,7 +126,7 @@ static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
     }
     // Expr insertion.
     // ==========================
-    if (i->symbol.set()) {
+    if (i->symbol) {
         ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
         if (j != attrs->attrs.end()) {
             // This attr path is already defined. However, if both
@@ -139,11 +139,11 @@ static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
                 for (auto & ad : ae->attrs) {
                     auto j2 = jAttrs->attrs.find(ad.first);
                     if (j2 != jAttrs->attrs.end()) // Attr already defined in iAttrs, error.
-                        dupAttr(ad.first, j2->second.pos, ad.second.pos);
+                        dupAttr(state, ad.first, j2->second.pos, ad.second.pos);
                     jAttrs->attrs.emplace(ad.first, ad.second);
                 }
             } else {
-                dupAttr(attrPath, pos, j->second.pos);
+                dupAttr(state, attrPath, pos, j->second.pos);
             }
         } else {
             // This attr path is not defined. Let's create it.
@@ -157,14 +157,14 @@ static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
 
 
 static Formals * toFormals(ParseData & data, ParserFormals * formals,
-    Pos pos = noPos, Symbol arg = {})
+    PosIdx pos = noPos, SymbolIdx arg = {})
 {
     std::sort(formals->formals.begin(), formals->formals.end(),
         [] (const auto & a, const auto & b) {
             return std::tie(a.name, a.pos) < std::tie(b.name, b.pos);
         });
 
-    std::optional<std::pair<Symbol, Pos>> duplicate;
+    std::optional<std::pair<SymbolIdx, PosIdx>> duplicate;
     for (size_t i = 0; i + 1 < formals->formals.size(); i++) {
         if (formals->formals[i].name != formals->formals[i + 1].name)
             continue;
@@ -173,18 +173,18 @@ static Formals * toFormals(ParseData & data, ParserFormals * formals,
     }
     if (duplicate)
         throw ParseError({
-            .msg = hintfmt("duplicate formal function argument '%1%'", duplicate->first),
+            .msg = hintfmt("duplicate formal function argument '%1%'", data.symbols[duplicate->first]),
-            .errPos = duplicate->second
+            .errPos = data.state.positions[duplicate->second]
         });
 
     Formals result;
     result.ellipsis = formals->ellipsis;
     result.formals = std::move(formals->formals);
 
-    if (arg.set() && result.has(arg))
+    if (arg && result.has(arg))
         throw ParseError({
-            .msg = hintfmt("duplicate formal function argument '%1%'", arg),
+            .msg = hintfmt("duplicate formal function argument '%1%'", data.symbols[arg]),
-            .errPos = pos
+            .errPos = data.state.positions[pos]
         });
 
     delete formals;
@@ -192,8 +192,8 @@ static Formals * toFormals(ParseData & data, ParserFormals * formals,
 }
 
 
-static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols,
+static Expr * stripIndentation(const PosIdx pos, SymbolTable & symbols,
-    std::vector<std::pair<Pos, std::variant<Expr *, StringToken> > > & es)
+    std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken> > > & es)
 {
     if (es.empty()) return new ExprString("");
 
@@ -233,7 +233,7 @@ static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols,
     }
 
     /* Strip spaces from each line. */
-    std::vector<std::pair<Pos, Expr *> > * es2 = new std::vector<std::pair<Pos, Expr *> >;
+    auto * es2 = new std::vector<std::pair<PosIdx, Expr *> >;
     atStartOfLine = true;
     size_t curDropped = 0;
     size_t n = es.size();
@@ -284,9 +284,9 @@ static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols,
 }
 
 
-static inline Pos makeCurPos(const YYLTYPE & loc, ParseData * data)
+static inline PosIdx makeCurPos(const YYLTYPE & loc, ParseData * data)
 {
-    return Pos(data->origin, data->file, loc.first_line, loc.first_column);
+    return data->state.positions.add(data->origin, loc.first_line, loc.first_column);
 }
 
 #define CUR_POS makeCurPos(*yylocp, data)
@@ -299,7 +299,7 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
 {
     data->error = {
         .msg = hintfmt(error),
-        .errPos = makeCurPos(*loc, data)
+        .errPos = data->state.positions[makeCurPos(*loc, data)]
     };
 }
 
@@ -320,8 +320,8 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
   StringToken uri;
   StringToken str;
   std::vector<nix::AttrName> * attrNames;
-  std::vector<std::pair<nix::Pos, nix::Expr *> > * string_parts;
+  std::vector<std::pair<nix::PosIdx, nix::Expr *> > * string_parts;
-  std::vector<std::pair<nix::Pos, std::variant<nix::Expr *, StringToken> > > * ind_string_parts;
+  std::vector<std::pair<nix::PosIdx, std::variant<nix::Expr *, StringToken> > > * ind_string_parts;
 }
 
 %type <e> start expr expr_function expr_if expr_op
@@ -369,15 +369,15 @@ expr_function
   : ID ':' expr_function
     { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), 0, $3); }
   | '{' formals '}' ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create(""), toFormals(*data, $2), $5); }
+    { $$ = new ExprLambda(CUR_POS, toFormals(*data, $2), $5); }
   | '{' formals '}' '@' ID ':' expr_function
     {
-      Symbol arg = data->symbols.create($5);
+      auto arg = data->symbols.create($5);
       $$ = new ExprLambda(CUR_POS, arg, toFormals(*data, $2, CUR_POS, arg), $7);
     }
   | ID '@' '{' formals '}' ':' expr_function
     {
-      Symbol arg = data->symbols.create($1);
+      auto arg = data->symbols.create($1);
       $$ = new ExprLambda(CUR_POS, arg, toFormals(*data, $4, CUR_POS, arg), $7);
     }
   | ASSERT expr ';' expr_function
@@ -388,7 +388,7 @@ expr_function
     { if (!$2->dynamicAttrs.empty())
         throw ParseError({
             .msg = hintfmt("dynamic attributes not allowed in let"),
-            .errPos = CUR_POS
+            .errPos = data->state.positions[CUR_POS]
         });
       $$ = new ExprLet($2, $4);
     }
@@ -415,7 +415,7 @@ expr_op
   | expr_op UPDATE expr_op { $$ = new ExprOpUpdate(CUR_POS, $1, $3); }
   | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, *$3); }
   | expr_op '+' expr_op
-    { $$ = new ExprConcatStrings(CUR_POS, false, new std::vector<std::pair<Pos, Expr *> >({{makeCurPos(@1, data), $1}, {makeCurPos(@3, data), $3}})); }
+    { $$ = new ExprConcatStrings(CUR_POS, false, new std::vector<std::pair<PosIdx, Expr *> >({{makeCurPos(@1, data), $1}, {makeCurPos(@3, data), $3}})); }
   | expr_op '-' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__sub")), {$1, $3}); }
   | expr_op '*' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__mul")), {$1, $3}); }
   | expr_op '/' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__div")), {$1, $3}); }
@@ -477,7 +477,7 @@ expr_simple
       if (noURLLiterals)
           throw ParseError({
               .msg = hintfmt("URL literals are disabled"),
-              .errPos = CUR_POS
+              .errPos = data->state.positions[CUR_POS]
           });
       $$ = new ExprString(std::string($1));
   }
@@ -503,9 +503,9 @@ string_parts_interpolated
   : string_parts_interpolated STR
   { $$ = $1; $1->emplace_back(makeCurPos(@2, data), new ExprString(std::string($2))); }
   | string_parts_interpolated DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(makeCurPos(@2, data), $3); }
-  | DOLLAR_CURLY expr '}' { $$ = new std::vector<std::pair<Pos, Expr *> >; $$->emplace_back(makeCurPos(@1, data), $2); }
+  | DOLLAR_CURLY expr '}' { $$ = new std::vector<std::pair<PosIdx, Expr *> >; $$->emplace_back(makeCurPos(@1, data), $2); }
   | STR DOLLAR_CURLY expr '}' {
-      $$ = new std::vector<std::pair<Pos, Expr *> >;
+      $$ = new std::vector<std::pair<PosIdx, Expr *> >;
       $$->emplace_back(makeCurPos(@1, data), new ExprString(std::string($1)));
       $$->emplace_back(makeCurPos(@2, data), $3);
     }
@@ -528,17 +528,17 @@ path_start
 ind_string_parts
   : ind_string_parts IND_STR { $$ = $1; $1->emplace_back(makeCurPos(@2, data), $2); }
   | ind_string_parts DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(makeCurPos(@2, data), $3); }
-  | { $$ = new std::vector<std::pair<Pos, std::variant<Expr *, StringToken> > >; }
+  | { $$ = new std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken> > >; }
   ;
 
 binds
-  : binds attrpath '=' expr ';' { $$ = $1; addAttr($$, *$2, $4, makeCurPos(@2, data)); }
+  : binds attrpath '=' expr ';' { $$ = $1; addAttr($$, *$2, $4, makeCurPos(@2, data), data->state); }
   | binds INHERIT attrs ';'
     { $$ = $1;
       for (auto & i : *$3) {
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
-              dupAttr(i.symbol, makeCurPos(@3, data), $$->attrs[i.symbol].pos);
+              dupAttr(data->state, i.symbol, makeCurPos(@3, data), $$->attrs[i.symbol].pos);
-          Pos pos = makeCurPos(@3, data);
+          auto pos = makeCurPos(@3, data);
           $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprVar(CUR_POS, i.symbol), pos, true));
       }
     }
@@ -547,7 +547,7 @@ binds
       /* !!! Should ensure sharing of the expression in $4. */
       for (auto & i : *$6) {
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
-              dupAttr(i.symbol, makeCurPos(@6, data), $$->attrs[i.symbol].pos);
+              dupAttr(data->state, i.symbol, makeCurPos(@6, data), $$->attrs[i.symbol].pos);
           $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprSelect(CUR_POS, $4, i.symbol), makeCurPos(@6, data)));
       }
     }
@@ -565,7 +565,7 @@ attrs
       } else
           throw ParseError({
               .msg = hintfmt("dynamic attributes not allowed in inherit"),
-              .errPos = makeCurPos(@2, data)
+              .errPos = data->state.positions[makeCurPos(@2, data)]
           });
     }
   | { $$ = new AttrPath; }
@@ -621,8 +621,8 @@ formals
   ;
 
 formal
-  : ID { $$ = new Formal(CUR_POS, data->symbols.create($1), 0); }
+  : ID { $$ = new Formal{CUR_POS, data->symbols.create($1), 0}; }
-  | ID '?' expr { $$ = new Formal(CUR_POS, data->symbols.create($1), $3); }
+  | ID '?' expr { $$ = new Formal{CUR_POS, data->symbols.create($1), $3}; }
   ;
 
 %%
@@ -646,19 +646,19 @@ Expr * EvalState::parse(char * text, size_t length, FileOrigin origin,
     const PathView path, const PathView basePath, StaticEnv & staticEnv)
 {
     yyscan_t scanner;
-    ParseData data(*this);
+    std::string file;
-    data.origin = origin;
     switch (origin) {
         case foFile:
-            data.file = data.symbols.create(path);
+            file = path;
             break;
         case foStdin:
         case foString:
-            data.file = data.symbols.create(text);
+            file = text;
             break;
         default:
             assert(false);
     }
+    ParseData data(*this, {file, origin});
     data.basePath = basePath;
 
     yylex_init(&scanner);
@@ -668,7 +668,7 @@ Expr * EvalState::parse(char * text, size_t length, FileOrigin origin,
 
     if (res) throw ParseError(data.error.value());
 
-    data.result->bindVars(staticEnv);
+    data.result->bindVars(*this, staticEnv);
 
     return data.result;
 }
@@ -760,7 +760,7 @@ Path EvalState::findFile(const std::string_view path)
 }
 
 
-Path EvalState::findFile(SearchPath & searchPath, const std::string_view path, const Pos & pos)
+Path EvalState::findFile(SearchPath & searchPath, const std::string_view path, const PosIdx pos)
 {
     for (auto & i : searchPath) {
         std::string suffix;
@@ -787,7 +787,7 @@ Path EvalState::findFile(SearchPath & searchPath, const std::string_view path, c
             ? "cannot look up '<%s>' in pure evaluation mode (use '--impure' to override)"
             : "file '%s' was not found in the Nix search path (add it using $NIX_PATH or -I)",
             path),
-        .errPos = pos
+        .errPos = positions[pos]
     });
 }
 

src/libexpr/primops.hh

@@ -38,9 +38,9 @@ struct RegisterPrimOp
    them. */
 
 /* Load a ValueInitializer from a DSO and return whatever it initializes */
-void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value & v);
+void prim_importNative(EvalState & state, const PosIdx pos, Value * * args, Value & v);
 
 /* Execute a program and parse its output */
-void prim_exec(EvalState & state, const Pos & pos, Value * * args, Value & v);
+void prim_exec(EvalState & state, const PosIdx pos, Value * * args, Value & v);
 
 }

src/libexpr/primops/context.cc

@@ -5,7 +5,7 @@
 
 namespace nix {
 
-static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_unsafeDiscardStringContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
     auto s = state.coerceToString(pos, *args[0], context);
@@ -15,7 +15,7 @@ static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos,
 static RegisterPrimOp primop_unsafeDiscardStringContext("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
 
 
-static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_hasContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
     state.forceString(*args[0], context, pos);
@@ -31,7 +31,7 @@ static RegisterPrimOp primop_hasContext("__hasContext", 1, prim_hasContext);
    source-only deployment).  This primop marks the string context so
    that builtins.derivation adds the path to drv.inputSrcs rather than
    drv.inputDrvs. */
-static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
     auto s = state.coerceToString(pos, *args[0], context);
@@ -65,7 +65,7 @@ static RegisterPrimOp primop_unsafeDiscardOutputDependency("__unsafeDiscardOutpu
    Note that for a given path any combination of the above attributes
    may be present.
 */
-static void prim_getContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     struct ContextInfo {
         bool path = false;
@@ -134,7 +134,7 @@ static RegisterPrimOp primop_getContext("__getContext", 1, prim_getContext);
    See the commentary above unsafeGetContext for details of the
    context representation.
 */
-static void prim_appendContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
     auto orig = state.forceString(*args[0], context, pos);
@@ -144,45 +144,46 @@ static void prim_appendContext(EvalState & state, const Pos & pos, Value * * arg
     auto sPath = state.symbols.create("path");
     auto sAllOutputs = state.symbols.create("allOutputs");
     for (auto & i : *args[1]->attrs) {
-        if (!state.store->isStorePath(i.name))
+        const auto & name = state.symbols[i.name];
+        if (!state.store->isStorePath(name))
             throw EvalError({
-                .msg = hintfmt("Context key '%s' is not a store path", i.name),
+                .msg = hintfmt("Context key '%s' is not a store path", name),
-                .errPos = *i.pos
+                .errPos = state.positions[i.pos]
             });
         if (!settings.readOnlyMode)
-            state.store->ensurePath(state.store->parseStorePath(i.name));
+            state.store->ensurePath(state.store->parseStorePath(name));
-        state.forceAttrs(*i.value, *i.pos);
+        state.forceAttrs(*i.value, i.pos);
         auto iter = i.value->attrs->find(sPath);
         if (iter != i.value->attrs->end()) {
-            if (state.forceBool(*iter->value, *iter->pos))
+            if (state.forceBool(*iter->value, iter->pos))
-                context.insert(i.name);
+                context.emplace(name);
         }
 
         iter = i.value->attrs->find(sAllOutputs);
         if (iter != i.value->attrs->end()) {
-            if (state.forceBool(*iter->value, *iter->pos)) {
+            if (state.forceBool(*iter->value, iter->pos)) {
-                if (!isDerivation(i.name)) {
+                if (!isDerivation(name)) {
                     throw EvalError({
-                        .msg = hintfmt("Tried to add all-outputs context of %s, which is not a derivation, to a string", i.name),
+                        .msg = hintfmt("Tried to add all-outputs context of %s, which is not a derivation, to a string", name),
-                        .errPos = *i.pos
+                        .errPos = state.positions[i.pos]
                     });
                 }
-                context.insert("=" + std::string(i.name));
+                context.insert(concatStrings("=", name));
             }
         }
 
         iter = i.value->attrs->find(state.sOutputs);
         if (iter != i.value->attrs->end()) {
-            state.forceList(*iter->value, *iter->pos);
+            state.forceList(*iter->value, iter->pos);
-            if (iter->value->listSize() && !isDerivation(i.name)) {
+            if (iter->value->listSize() && !isDerivation(name)) {
                 throw EvalError({
-                    .msg = hintfmt("Tried to add derivation output context of %s, which is not a derivation, to a string", i.name),
+                    .msg = hintfmt("Tried to add derivation output context of %s, which is not a derivation, to a string", name),
-                    .errPos = *i.pos
+                    .errPos = state.positions[i.pos]
                 });
             }
             for (auto elem : iter->value->listItems()) {
-                auto name = state.forceStringNoCtx(*elem, *iter->pos);
+                auto outputName = state.forceStringNoCtx(*elem, iter->pos);
-                context.insert(concatStrings("!", name, "!", i.name));
+                context.insert(concatStrings("!", outputName, "!", name));
             }
         }
     }

src/libexpr/primops/fetchClosure.cc

@@ -5,7 +5,7 @@
 
 namespace nix {
 
-static void prim_fetchClosure(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     state.forceAttrs(*args[0], pos);
 
@@ -15,40 +15,42 @@ static void prim_fetchClosure(EvalState & state, const Pos & pos, Value * * args
     std::optional<StorePath> toPath;
 
     for (auto & attr : *args[0]->attrs) {
-        if (attr.name == "fromPath") {
+        const auto & attrName = state.symbols[attr.name];
+
+        if (attrName == "fromPath") {
             PathSet context;
-            fromPath = state.coerceToStorePath(*attr.pos, *attr.value, context);
+            fromPath = state.coerceToStorePath(attr.pos, *attr.value, context);
         }
 
-        else if (attr.name == "toPath") {
+        else if (attrName == "toPath") {
-            state.forceValue(*attr.value, *attr.pos);
+            state.forceValue(*attr.value, attr.pos);
             toCA = true;
             if (attr.value->type() != nString || attr.value->string.s != std::string("")) {
                 PathSet context;
-                toPath = state.coerceToStorePath(*attr.pos, *attr.value, context);
+                toPath = state.coerceToStorePath(attr.pos, *attr.value, context);
             }
         }
 
-        else if (attr.name == "fromStore")
+        else if (attrName == "fromStore")
-            fromStoreUrl = state.forceStringNoCtx(*attr.value, *attr.pos);
+            fromStoreUrl = state.forceStringNoCtx(*attr.value, attr.pos);
 
         else
             throw Error({
-                .msg = hintfmt("attribute '%s' isn't supported in call to 'fetchClosure'", attr.name),
+                .msg = hintfmt("attribute '%s' isn't supported in call to 'fetchClosure'", attrName),
-                .errPos = pos
+                .errPos = state.positions[pos]
             });
     }
 
     if (!fromPath)
         throw Error({
             .msg = hintfmt("attribute '%s' is missing in call to 'fetchClosure'", "fromPath"),
-            .errPos = pos
+            .errPos = state.positions[pos]
         });
 
     if (!fromStoreUrl)
         throw Error({
             .msg = hintfmt("attribute '%s' is missing in call to 'fetchClosure'", "fromStore"),
-            .errPos = pos
+            .errPos = state.positions[pos]
         });
 
     auto parsedURL = parseURL(*fromStoreUrl);
@@ -58,13 +60,13 @@ static void prim_fetchClosure(EvalState & state, const Pos & pos, Value * * args
         !(getEnv("_NIX_IN_TEST").has_value() && parsedURL.scheme == "file"))
         throw Error({
             .msg = hintfmt("'fetchClosure' only supports http:// and https:// stores"),
-            .errPos = pos
+            .errPos = state.positions[pos]
         });
 
     if (!parsedURL.query.empty())
         throw Error({
             .msg = hintfmt("'fetchClosure' does not support URL query parameters (in '%s')", *fromStoreUrl),
-            .errPos = pos
+            .errPos = state.positions[pos]
         });
 
     auto fromStore = openStore(parsedURL.to_string());
@@ -80,7 +82,7 @@ static void prim_fetchClosure(EvalState & state, const Pos & pos, Value * * args
                         state.store->printStorePath(*fromPath),
                         state.store->printStorePath(i->second),
                         state.store->printStorePath(*toPath)),
-                    .errPos = pos
+                    .errPos = state.positions[pos]
                 });
             if (!toPath)
                 throw Error({
@@ -89,7 +91,7 @@ static void prim_fetchClosure(EvalState & state, const Pos & pos, Value * * args
                         "please set this in the 'toPath' attribute passed to 'fetchClosure'",
                         state.store->printStorePath(*fromPath),
                         state.store->printStorePath(i->second)),
-                    .errPos = pos
+                    .errPos = state.positions[pos]
                 });
         }
     } else {
@@ -105,7 +107,7 @@ static void prim_fetchClosure(EvalState & state, const Pos & pos, Value * * args
             throw Error({
                 .msg = hintfmt("in pure mode, 'fetchClosure' requires a content-addressed path, which '%s' isn't",
                     state.store->printStorePath(*toPath)),
-                .errPos = pos
+                .errPos = state.positions[pos]
             });
     }
 

src/libexpr/primops/fetchMercurial.cc

@@ -7,7 +7,7 @@
 
 namespace nix {
 
-static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     std::string url;
     std::optional<Hash> rev;
@@ -22,31 +22,31 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
         state.forceAttrs(*args[0], pos);
 
         for (auto & attr : *args[0]->attrs) {
-            std::string_view n(attr.name);
+            std::string_view n(state.symbols[attr.name]);
             if (n == "url")
-                url = state.coerceToString(*attr.pos, *attr.value, context, false, false).toOwned();
+                url = state.coerceToString(attr.pos, *attr.value, context, false, false).toOwned();
             else if (n == "rev") {
                 // Ugly: unlike fetchGit, here the "rev" attribute can
                 // be both a revision or a branch/tag name.
-                auto value = state.forceStringNoCtx(*attr.value, *attr.pos);
+                auto value = state.forceStringNoCtx(*attr.value, attr.pos);
                 if (std::regex_match(value.begin(), value.end(), revRegex))
                     rev = Hash::parseAny(value, htSHA1);
                 else
                     ref = value;
             }
             else if (n == "name")
-                name = state.forceStringNoCtx(*attr.value, *attr.pos);
+                name = state.forceStringNoCtx(*attr.value, attr.pos);
             else
                 throw EvalError({
-                    .msg = hintfmt("unsupported argument '%s' to 'fetchMercurial'", attr.name),
+                    .msg = hintfmt("unsupported argument '%s' to 'fetchMercurial'", state.symbols[attr.name]),
-                    .errPos = *attr.pos
+                    .errPos = state.positions[attr.pos]
                 });
         }
 
         if (url.empty())
             throw EvalError({
                 .msg = hintfmt("'url' argument required"),
-                .errPos = pos
+                .errPos = state.positions[pos]
             });
 
     } else

src/libexpr/primops/fetchTree.cc

@@ -90,7 +90,7 @@ struct FetchTreeParams {
 
 static void fetchTree(
     EvalState & state,
-    const Pos & pos,
+    const PosIdx pos,
     Value * * args,
     Value & v,
     std::optional<std::string> type,
@@ -110,43 +110,43 @@ static void fetchTree(
             if (type)
                 throw Error({
                     .msg = hintfmt("unexpected attribute 'type'"),
-                    .errPos = pos
+                    .errPos = state.positions[pos]
                 });
-            type = state.forceStringNoCtx(*aType->value, *aType->pos);
+            type = state.forceStringNoCtx(*aType->value, aType->pos);
         } else if (!type)
             throw Error({
                 .msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
-                .errPos = pos
+                .errPos = state.positions[pos]
             });
 
         attrs.emplace("type", type.value());
 
         for (auto & attr : *args[0]->attrs) {
             if (attr.name == state.sType) continue;
-            state.forceValue(*attr.value, *attr.pos);
+            state.forceValue(*attr.value, attr.pos);
             if (attr.value->type() == nPath || attr.value->type() == nString) {
-                auto s = state.coerceToString(*attr.pos, *attr.value, context, false, false).toOwned();
+                auto s = state.coerceToString(attr.pos, *attr.value, context, false, false).toOwned();
-                attrs.emplace(attr.name,
+                attrs.emplace(state.symbols[attr.name],
-                    attr.name == "url"
+                    state.symbols[attr.name] == "url"
                     ? type == "git"
                       ? fixURIForGit(s, state)
                       : fixURI(s, state)
                     : s);
             }
             else if (attr.value->type() == nBool)
-                attrs.emplace(attr.name, Explicit<bool>{attr.value->boolean});
+                attrs.emplace(state.symbols[attr.name], Explicit<bool>{attr.value->boolean});
             else if (attr.value->type() == nInt)
-                attrs.emplace(attr.name, uint64_t(attr.value->integer));
+                attrs.emplace(state.symbols[attr.name], uint64_t(attr.value->integer));
             else
                 throw TypeError("fetchTree argument '%s' is %s while a string, Boolean or integer is expected",
-                    attr.name, showType(*attr.value));
+                    state.symbols[attr.name], showType(*attr.value));
         }
 
         if (!params.allowNameArgument)
             if (auto nameIter = attrs.find("name"); nameIter != attrs.end())
                 throw Error({
                     .msg = hintfmt("attribute 'name' isn't supported in call to 'fetchTree'"),
-                    .errPos = pos
+                    .errPos = state.positions[pos]
                 });
 
         input = fetchers::Input::fromAttrs(std::move(attrs));
@@ -167,7 +167,7 @@ static void fetchTree(
         input = lookupInRegistries(state.store, input).first;
 
     if (evalSettings.pureEval && !input.isLocked())
-        throw Error("in pure evaluation mode, 'fetchTree' requires a locked input, at %s", pos);
+        throw Error("in pure evaluation mode, 'fetchTree' requires a locked input, at %s", state.positions[pos]);
 
     auto [tree, input2] = input.fetch(state.store);
 
@@ -176,7 +176,7 @@ static void fetchTree(
     emitTreeAttrs(state, tree, input2, v, params.emptyRevFallback, false);
 }
 
-static void prim_fetchTree(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_fetchTree(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     settings.requireExperimentalFeature(Xp::Flakes);
     fetchTree(state, pos, args, v, std::nullopt, FetchTreeParams { .allowNameArgument = false });
@@ -185,7 +185,7 @@ static void prim_fetchTree(EvalState & state, const Pos & pos, Value * * args, V
 // FIXME: document
 static RegisterPrimOp primop_fetchTree("fetchTree", 1, prim_fetchTree);
 
-static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
+static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v,
     const std::string & who, bool unpack, std::string name)
 {
     std::optional<std::string> url;
@@ -198,24 +198,24 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
         state.forceAttrs(*args[0], pos);
 
         for (auto & attr : *args[0]->attrs) {
-            std::string n(attr.name);
+            std::string_view n(state.symbols[attr.name]);
             if (n == "url")
-                url = state.forceStringNoCtx(*attr.value, *attr.pos);
+                url = state.forceStringNoCtx(*attr.value, attr.pos);
             else if (n == "sha256")
-                expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA256);
+                expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, attr.pos), htSHA256);
             else if (n == "name")
-                name = state.forceStringNoCtx(*attr.value, *attr.pos);
+                name = state.forceStringNoCtx(*attr.value, attr.pos);
             else
                 throw EvalError({
-                    .msg = hintfmt("unsupported argument '%s' to '%s'", attr.name, who),
+                    .msg = hintfmt("unsupported argument '%s' to '%s'", n, who),
-                    .errPos = *attr.pos
+                    .errPos = state.positions[attr.pos]
                 });
             }
 
         if (!url)
             throw EvalError({
                 .msg = hintfmt("'url' argument required"),
-                .errPos = pos
+                .errPos = state.positions[pos]
             });
     } else
         url = state.forceStringNoCtx(*args[0], pos);
@@ -262,7 +262,7 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
     state.allowAndSetStorePathString(storePath, v);
 }
 
-static void prim_fetchurl(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_fetchurl(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     fetch(state, pos, args, v, "fetchurl", false, "");
 }
@@ -278,7 +278,7 @@ static RegisterPrimOp primop_fetchurl({
     .fun = prim_fetchurl,
 });
 
-static void prim_fetchTarball(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_fetchTarball(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     fetch(state, pos, args, v, "fetchTarball", true, "source");
 }
@@ -329,7 +329,7 @@ static RegisterPrimOp primop_fetchTarball({
     .fun = prim_fetchTarball,
 });
 
-static void prim_fetchGit(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_fetchGit(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     fetchTree(state, pos, args, v, "git", FetchTreeParams { .emptyRevFallback = true, .allowNameArgument = true });
 }

src/libexpr/primops/fromTOML.cc

@@ -5,7 +5,7 @@
 
 namespace nix {
 
-static void prim_fromTOML(EvalState & state, const Pos & pos, Value * * args, Value & val)
+static void prim_fromTOML(EvalState & state, const PosIdx pos, Value * * args, Value & val)
 {
     auto toml = state.forceStringNoCtx(*args[0], pos);
 
@@ -73,7 +73,7 @@ static void prim_fromTOML(EvalState & state, const Pos & pos, Value * * args, Va
     } catch (std::exception & e) { // TODO: toml::syntax_error
         throw EvalError({
             .msg = hintfmt("while parsing a TOML string: %s", e.what()),
-            .errPos = pos
+            .errPos = state.positions[pos]
         });
     }
 }

src/libexpr/symbol-table.hh

@@ -5,6 +5,7 @@
 #include <unordered_map>
 
 #include "types.hh"
+#include "chunked-vector.hh"
 
 namespace nix {
 
@@ -16,90 +17,90 @@ namespace nix {
 
 class Symbol
 {
-private:
-    const std::string * s; // pointer into SymbolTable
-    Symbol(const std::string * s) : s(s) { };
     friend class SymbolTable;
+private:
+    std::string s;
 
 public:
-    Symbol() : s(0) { };
+    Symbol(std::string_view s) : s(s) { }
-
-    bool operator == (const Symbol & s2) const
-    {
-        return s == s2.s;
-    }
 
     // FIXME: remove
     bool operator == (std::string_view s2) const
     {
-        return s->compare(s2) == 0;
+        return s == s2;
-    }
-
-    bool operator != (const Symbol & s2) const
-    {
-        return s != s2.s;
-    }
-
-    bool operator < (const Symbol & s2) const
-    {
-        return s < s2.s;
     }
 
     operator const std::string & () const
     {
-        return *s;
+        return s;
     }
 
     operator const std::string_view () const
-    {
-        return *s;
-    }
-
-    bool set() const
     {
         return s;
     }
 
-    bool empty() const
-    {
-        return s->empty();
-    }
-
     friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
 };
 
+class SymbolIdx
+{
+    friend class SymbolTable;
+
+private:
+    uint32_t id;
+
+    explicit SymbolIdx(uint32_t id): id(id) {}
+
+public:
+    SymbolIdx() : id(0) {}
+
+    explicit operator bool() const { return id > 0; }
+
+    bool operator<(const SymbolIdx other) const { return id < other.id; }
+    bool operator==(const SymbolIdx other) const { return id == other.id; }
+    bool operator!=(const SymbolIdx other) const { return id != other.id; }
+};
+
 class SymbolTable
 {
 private:
-    std::unordered_map<std::string_view, Symbol> symbols;
+    std::unordered_map<std::string_view, std::pair<const Symbol *, uint32_t>> symbols;
-    std::list<std::string> store;
+    ChunkedVector<Symbol, 8192> store{16};
 
 public:
-    Symbol create(std::string_view s)
+    SymbolIdx create(std::string_view s)
     {
         // Most symbols are looked up more than once, so we trade off insertion performance
         // for lookup performance.
         // TODO: could probably be done more efficiently with transparent Hash and Equals
         // on the original implementation using unordered_set
         auto it = symbols.find(s);
-        if (it != symbols.end()) return it->second;
+        if (it != symbols.end()) return SymbolIdx(it->second.second + 1);
 
-        auto & rawSym = store.emplace_back(s);
+        const auto & [rawSym, idx] = store.add(s);
-        return symbols.emplace(rawSym, Symbol(&rawSym)).first->second;
+        symbols.emplace(rawSym, std::make_pair(&rawSym, idx));
+        return SymbolIdx(idx + 1);
+    }
+
+    const Symbol & operator[](SymbolIdx s) const
+    {
+        if (s.id == 0 || s.id > store.size())
+            abort();
+        return store[s.id - 1];
     }
 
     size_t size() const
     {
-        return symbols.size();
+        return store.size();
     }
 
     size_t totalSize() const;
 
     template<typename T>
-    void dump(T callback)
+    void dump(T callback) const
     {
-        for (auto & s : store)
+        store.forEach(callback);
-            callback(s);
     }
 };
 

src/libexpr/value-to-json.cc

@@ -10,7 +10,7 @@
 namespace nix {
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const Pos & pos, JSONPlaceholder & out, PathSet & context)
+    Value & v, const PosIdx pos, JSONPlaceholder & out, PathSet & context)
 {
     checkInterrupt();
 
@@ -50,14 +50,14 @@ void printValueAsJSON(EvalState & state, bool strict,
                 auto obj(out.object());
                 StringSet names;
                 for (auto & j : *v.attrs)
-                    names.insert(j.name);
+                    names.emplace(state.symbols[j.name]);
                 for (auto & j : names) {
                     Attr & a(*v.attrs->find(state.symbols.create(j)));
                     auto placeholder(obj.placeholder(j));
-                    printValueAsJSON(state, strict, *a.value, *a.pos, placeholder, context);
+                    printValueAsJSON(state, strict, *a.value, a.pos, placeholder, context);
                 }
             } else
-                printValueAsJSON(state, strict, *i->value, *i->pos, out, context);
+                printValueAsJSON(state, strict, *i->value, i->pos, out, context);
             break;
         }
 
@@ -82,15 +82,15 @@ void printValueAsJSON(EvalState & state, bool strict,
         case nFunction:
             auto e = TypeError({
                 .msg = hintfmt("cannot convert %1% to JSON", showType(v)),
-                .errPos = v.determinePos(pos)
+                .errPos = state.positions[v.determinePos(pos)]
             });
-            e.addTrace(pos, hintfmt("message for the trace"));
+            e.addTrace(state.positions[pos], hintfmt("message for the trace"));
             throw e;
     }
 }
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const Pos & pos, std::ostream & str, PathSet & context)
+    Value & v, const PosIdx pos, std::ostream & str, PathSet & context)
 {
     JSONPlaceholder out(str);
     printValueAsJSON(state, strict, v, pos, out, context);

src/libexpr/value-to-json.hh

@@ -11,9 +11,9 @@ namespace nix {
 class JSONPlaceholder;
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const Pos & pos, JSONPlaceholder & out, PathSet & context);
+    Value & v, const PosIdx pos, JSONPlaceholder & out, PathSet & context);
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const Pos & pos, std::ostream & str, PathSet & context);
+    Value & v, const PosIdx pos, std::ostream & str, PathSet & context);
 
 }

src/libexpr/value-to-xml.cc

@@ -19,10 +19,10 @@ static XMLAttrs singletonAttrs(const std::string & name, const std::string & val
 
 static void printValueAsXML(EvalState & state, bool strict, bool location,
     Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
-    const Pos & pos);
+    const PosIdx pos);
 
 
-static void posToXML(XMLAttrs & xmlAttrs, const Pos & pos)
+static void posToXML(EvalState & state, XMLAttrs & xmlAttrs, const Pos & pos)
 {
     xmlAttrs["path"] = pos.file;
     xmlAttrs["line"] = (format("%1%") % pos.line).str();
@@ -36,25 +36,25 @@ static void showAttrs(EvalState & state, bool strict, bool location,
     StringSet names;
 
     for (auto & i : attrs)
-        names.insert(i.name);
+        names.emplace(state.symbols[i.name]);
 
     for (auto & i : names) {
         Attr & a(*attrs.find(state.symbols.create(i)));
 
         XMLAttrs xmlAttrs;
         xmlAttrs["name"] = i;
-        if (location && a.pos != ptr(&noPos)) posToXML(xmlAttrs, *a.pos);
+        if (location && a.pos) posToXML(state, xmlAttrs, state.positions[a.pos]);
 
         XMLOpenElement _(doc, "attr", xmlAttrs);
         printValueAsXML(state, strict, location,
-            *a.value, doc, context, drvsSeen, *a.pos);
+            *a.value, doc, context, drvsSeen, a.pos);
     }
 }
 
 
 static void printValueAsXML(EvalState & state, bool strict, bool location,
     Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
-    const Pos & pos)
+    const PosIdx pos)
 {
     checkInterrupt();
 
@@ -93,14 +93,14 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
                 Path drvPath;
                 a = v.attrs->find(state.sDrvPath);
                 if (a != v.attrs->end()) {
-                    if (strict) state.forceValue(*a->value, *a->pos);
+                    if (strict) state.forceValue(*a->value, a->pos);
                     if (a->value->type() == nString)
                         xmlAttrs["drvPath"] = drvPath = a->value->string.s;
                 }
 
                 a = v.attrs->find(state.sOutPath);
                 if (a != v.attrs->end()) {
-                    if (strict) state.forceValue(*a->value, *a->pos);
+                    if (strict) state.forceValue(*a->value, a->pos);
                     if (a->value->type() == nString)
                         xmlAttrs["outPath"] = a->value->string.s;
                 }
@@ -134,18 +134,18 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
                 break;
             }
             XMLAttrs xmlAttrs;
-            if (location) posToXML(xmlAttrs, v.lambda.fun->pos);
+            if (location) posToXML(state, xmlAttrs, state.positions[v.lambda.fun->pos]);
             XMLOpenElement _(doc, "function", xmlAttrs);
 
             if (v.lambda.fun->hasFormals()) {
                 XMLAttrs attrs;
-                if (!v.lambda.fun->arg.empty()) attrs["name"] = v.lambda.fun->arg;
+                if (v.lambda.fun->arg) attrs["name"] = state.symbols[v.lambda.fun->arg];
                 if (v.lambda.fun->formals->ellipsis) attrs["ellipsis"] = "1";
                 XMLOpenElement _(doc, "attrspat", attrs);
-                for (auto & i : v.lambda.fun->formals->lexicographicOrder())
+                for (auto & i : v.lambda.fun->formals->lexicographicOrder(state.symbols))
-                    doc.writeEmptyElement("attr", singletonAttrs("name", i.name));
+                    doc.writeEmptyElement("attr", singletonAttrs("name", state.symbols[i.name]));
             } else
-                doc.writeEmptyElement("varpat", singletonAttrs("name", v.lambda.fun->arg));
+                doc.writeEmptyElement("varpat", singletonAttrs("name", state.symbols[v.lambda.fun->arg]));
 
             break;
         }
@@ -166,14 +166,14 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
 
 void ExternalValueBase::printValueAsXML(EvalState & state, bool strict,
     bool location, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
-    const Pos & pos) const
+    const PosIdx pos) const
 {
     doc.writeEmptyElement("unevaluated");
 }
 
 
 void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, std::ostream & out, PathSet & context, const Pos & pos)
+    Value & v, std::ostream & out, PathSet & context, const PosIdx pos)
 {
     XMLWriter doc(true, out);
     XMLOpenElement root(doc, "expr");

src/libexpr/value-to-xml.hh

@@ -9,6 +9,6 @@
 namespace nix {
 
 void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, std::ostream & out, PathSet & context, const Pos & pos);
+    Value & v, std::ostream & out, PathSet & context, const PosIdx pos);
 
 }

src/libexpr/value.hh

@@ -55,7 +55,8 @@ struct Env;
 struct Expr;
 struct ExprLambda;
 struct PrimOp;
-class Symbol;
+class SymbolIdx;
+class PosIdx;
 struct Pos;
 class StorePath;
 class Store;
@@ -103,7 +104,7 @@ class ExternalValueBase
     /* Print the value as XML. Defaults to unevaluated */
     virtual void printValueAsXML(EvalState & state, bool strict, bool location,
         XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
-        const Pos & pos) const;
+        const PosIdx pos) const;
 
     virtual ~ExternalValueBase()
     {
@@ -120,11 +121,11 @@ private:
 
     friend std::string showType(const Value & v);
 
-    void print(std::ostream & str, std::set<const void *> * seen) const;
+    void print(const SymbolTable & symbols, std::ostream & str, std::set<const void *> * seen) const;
 
 public:
 
-    void print(std::ostream & str, bool showRepeated = false) const;
+    void print(const SymbolTable & symbols, std::ostream & str, bool showRepeated = false) const;
 
     // Functions needed to distinguish the type
     // These should be removed eventually, by putting the functionality that's
@@ -252,7 +253,7 @@ public:
 
     inline void mkString(const Symbol & s)
     {
-        mkString(((const std::string &) s).c_str());
+        mkString(std::string_view(s).data());
     }
 
     inline void mkPath(const char * s)
@@ -368,7 +369,7 @@ public:
         return internalType == tList1 ? 1 : internalType == tList2 ? 2 : bigList.size;
     }
 
-    Pos determinePos(const Pos & pos) const;
+    PosIdx determinePos(const PosIdx pos) const;
 
     /* Check whether forcing this value requires a trivial amount of
        computation. In particular, function applications are
@@ -409,12 +410,12 @@ public:
 
 #if HAVE_BOEHMGC
 typedef std::vector<Value *, traceable_allocator<Value *> > ValueVector;
-typedef std::map<Symbol, Value *, std::less<Symbol>, traceable_allocator<std::pair<const Symbol, Value *> > > ValueMap;
+typedef std::map<SymbolIdx, Value *, std::less<SymbolIdx>, traceable_allocator<std::pair<const SymbolIdx, Value *> > > ValueMap;
-typedef std::map<Symbol, ValueVector, std::less<Symbol>, traceable_allocator<std::pair<const Symbol, ValueVector> > > ValueVectorMap;
+typedef std::map<SymbolIdx, ValueVector, std::less<SymbolIdx>, traceable_allocator<std::pair<const SymbolIdx, ValueVector> > > ValueVectorMap;
 #else
 typedef std::vector<Value *> ValueVector;
-typedef std::map<Symbol, Value *> ValueMap;
+typedef std::map<SymbolIdx, Value *> ValueMap;
-typedef std::map<Symbol, ValueVector> ValueVectorMap;
+typedef std::map<SymbolIdx, ValueVector> ValueVectorMap;
 #endif
 
 

src/libfetchers/mercurial.cc

@@ -36,7 +36,7 @@ static std::string runHg(const Strings & args, const std::optional<std::string>
     auto res = runProgram(std::move(opts));
 
     if (!statusOk(res.first))
-        throw ExecError(res.first, fmt("hg %1%", statusToString(res.first)));
+        throw ExecError(res.first, "hg %1%", statusToString(res.first));
 
     return res.second;
 }
@@ -273,7 +273,7 @@ struct MercurialInputScheme : InputScheme
                         runHg({ "recover", "-R", cacheDir });
                         runHg({ "pull", "-R", cacheDir, "--", actualUrl });
                     } else {
-                        throw ExecError(e.status, fmt("'hg pull' %s", statusToString(e.status)));
+                        throw ExecError(e.status, "'hg pull' %s", statusToString(e.status));
                     }
                 }
             } else {

src/libmain/shared.cc

@@ -60,37 +60,37 @@ void printMissing(ref<Store> store, const StorePathSet & willBuild,
 {
     if (!willBuild.empty()) {
         if (willBuild.size() == 1)
-            printMsg(lvl, fmt("this derivation will be built:"));
+            printMsg(lvl, "this derivation will be built:");
         else
-            printMsg(lvl, fmt("these %d derivations will be built:", willBuild.size()));
+            printMsg(lvl, "these %d derivations will be built:", willBuild.size());
         auto sorted = store->topoSortPaths(willBuild);
         reverse(sorted.begin(), sorted.end());
         for (auto & i : sorted)
-            printMsg(lvl, fmt("  %s", store->printStorePath(i)));
+            printMsg(lvl, "  %s", store->printStorePath(i));
     }
 
     if (!willSubstitute.empty()) {
         const float downloadSizeMiB = downloadSize / (1024.f * 1024.f);
         const float narSizeMiB = narSize / (1024.f * 1024.f);
         if (willSubstitute.size() == 1) {
-            printMsg(lvl, fmt("this path will be fetched (%.2f MiB download, %.2f MiB unpacked):",
+            printMsg(lvl, "this path will be fetched (%.2f MiB download, %.2f MiB unpacked):",
                 downloadSizeMiB,
-                narSizeMiB));
+                narSizeMiB);
         } else {
-            printMsg(lvl, fmt("these %d paths will be fetched (%.2f MiB download, %.2f MiB unpacked):",
+            printMsg(lvl, "these %d paths will be fetched (%.2f MiB download, %.2f MiB unpacked):",
                 willSubstitute.size(),
                 downloadSizeMiB,
-                narSizeMiB));
+                narSizeMiB);
         }
         for (auto & i : willSubstitute)
-            printMsg(lvl, fmt("  %s", store->printStorePath(i)));
+            printMsg(lvl, "  %s", store->printStorePath(i));
     }
 
     if (!unknown.empty()) {
-        printMsg(lvl, fmt("don't know how to build these paths%s:",
+        printMsg(lvl, "don't know how to build these paths%s:",
-                (settings.readOnlyMode ? " (may be caused by read-only store access)" : "")));
+                (settings.readOnlyMode ? " (may be caused by read-only store access)" : ""));
         for (auto & i : unknown)
-            printMsg(lvl, fmt("  %s", store->printStorePath(i)));
+            printMsg(lvl, "  %s", store->printStorePath(i));
     }
 }
 

src/libstore/ca-specific-schema.sql

@@ -13,12 +13,27 @@ create table if not exists Realisations (
 
 create index if not exists IndexRealisations on Realisations(drvPath, outputName);
 
+-- We can end-up in a weird edge-case where a path depends on itself because
+-- it’s an output of a CA derivation, that happens to be the same as one of its
+-- dependencies.
+-- In that case we have a dependency loop (path -> realisation1 -> realisation2
+-- -> path) that we need to break by removing the dependencies between the
+-- realisations
+create trigger if not exists DeleteSelfRefsViaRealisations before delete on ValidPaths
+  begin
+    delete from RealisationsRefs where realisationReference in (
+      select id from Realisations where outputPath = old.id
+    );
+  end;
+
 create table if not exists RealisationsRefs (
     referrer integer not null,
     realisationReference integer,
     foreign key (referrer) references Realisations(id) on delete cascade,
     foreign key (realisationReference) references Realisations(id) on delete restrict
 );
+-- used by deletion trigger
+create index if not exists IndexRealisationsRefsRealisationReference on RealisationsRefs(realisationReference);
 
 -- used by QueryRealisationReferences
 create index if not exists IndexRealisationsRefs on RealisationsRefs(referrer);

src/libstore/filetransfer.cc

@@ -443,14 +443,13 @@ struct curlFileTransfer : public FileTransfer
                     : httpStatus != 0
                     ? FileTransferError(err,
                         std::move(response),
-                        fmt("unable to %s '%s': HTTP error %d ('%s')",
+                        "unable to %s '%s': HTTP error %d%s",
-                            request.verb(), request.uri, httpStatus, statusMsg)
+                        request.verb(), request.uri, httpStatus,
-                        + (code == CURLE_OK ? "" : fmt(" (curl error: %s)", curl_easy_strerror(code)))
+                        code == CURLE_OK ? "" : fmt(" (curl error: %s)", curl_easy_strerror(code)))
-                        )
                     : FileTransferError(err,
                         std::move(response),
-                        fmt("unable to %s '%s': %s (%d)",
+                        "unable to %s '%s': %s (%d)",
-                            request.verb(), request.uri, curl_easy_strerror(code), code));
+                        request.verb(), request.uri, curl_easy_strerror(code), code);
 
                 /* If this is a transient error, then maybe retry the
                    download after a while. If we're writing to a
@@ -704,7 +703,7 @@ struct curlFileTransfer : public FileTransfer
                 auto s3Res = s3Helper.getObject(bucketName, key);
                 FileTransferResult res;
                 if (!s3Res.data)
-                    throw FileTransferError(NotFound, {}, "S3 object '%s' does not exist", request.uri);
+                    throw FileTransferError(NotFound, "S3 object '%s' does not exist", request.uri);
                 res.data = std::move(*s3Res.data);
                 callback(std::move(res));
 #else

src/libstore/local-store.cc

@@ -81,7 +81,7 @@ int getSchema(Path schemaPath)
 
 void migrateCASchema(SQLite& db, Path schemaPath, AutoCloseFD& lockFd)
 {
-    const int nixCASchemaVersion = 3;
+    const int nixCASchemaVersion = 4;
     int curCASchema = getSchema(schemaPath);
     if (curCASchema != nixCASchemaVersion) {
         if (curCASchema > nixCASchemaVersion) {
@@ -143,6 +143,21 @@ void migrateCASchema(SQLite& db, Path schemaPath, AutoCloseFD& lockFd)
             )");
             txn.commit();
         }
+        if (curCASchema < 4) {
+            SQLiteTxn txn(db);
+            db.exec(R"(
+                create trigger if not exists DeleteSelfRefsViaRealisations before delete on ValidPaths
+                begin
+                    delete from RealisationsRefs where realisationReference in (
+                    select id from Realisations where outputPath = old.id
+                    );
+                end;
+                -- used by deletion trigger
+                create index if not exists IndexRealisationsRefsRealisationReference on RealisationsRefs(realisationReference);
+            )");
+            txn.commit();
+        }
+
         writeFile(schemaPath, fmt("%d", nixCASchemaVersion));
         lockFile(lockFd.get(), ltRead, true);
     }
@@ -482,18 +497,18 @@ void LocalStore::openDB(State & state, bool create)
         SQLiteStmt stmt;
         stmt.create(db, "pragma main.journal_mode;");
         if (sqlite3_step(stmt) != SQLITE_ROW)
-            throwSQLiteError(db, "querying journal mode");
+            SQLiteError::throw_(db, "querying journal mode");
         prevMode = std::string((const char *) sqlite3_column_text(stmt, 0));
     }
     if (prevMode != mode &&
         sqlite3_exec(db, ("pragma main.journal_mode = " + mode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
-        throwSQLiteError(db, "setting journal mode");
+        SQLiteError::throw_(db, "setting journal mode");
 
     /* Increase the auto-checkpoint interval to 40000 pages.  This
        seems enough to ensure that instantiating the NixOS system
        derivation is done in a single fsync(). */
     if (mode == "wal" && sqlite3_exec(db, "pragma wal_autocheckpoint = 40000;", 0, 0, 0) != SQLITE_OK)
-        throwSQLiteError(db, "setting autocheckpoint interval");
+        SQLiteError::throw_(db, "setting autocheckpoint interval");
 
     /* Initialise the database schema, if necessary. */
     if (create) {

src/libstore/sqlite.cc

@@ -8,22 +8,32 @@
 
 namespace nix {
 
-[[noreturn]] void throwSQLiteError(sqlite3 * db, const FormatOrString & fs)
+SQLiteError::SQLiteError(const char *path, int errNo, int extendedErrNo, hintformat && hf)
+  : Error(""), path(path), errNo(errNo), extendedErrNo(extendedErrNo)
+{
+    err.msg = hintfmt("%s: %s (in '%s')",
+        normaltxt(hf.str()),
+        sqlite3_errstr(extendedErrNo),
+        path ? path : "(in-memory)");
+}
+
+[[noreturn]] void SQLiteError::throw_(sqlite3 * db, hintformat && hf)
 {
     int err = sqlite3_errcode(db);
     int exterr = sqlite3_extended_errcode(db);
 
     auto path = sqlite3_db_filename(db, nullptr);
-    if (!path) path = "(in-memory)";
 
     if (err == SQLITE_BUSY || err == SQLITE_PROTOCOL) {
-        throw SQLiteBusy(
+        auto exp = SQLiteBusy(path, err, exterr, std::move(hf));
+        exp.err.msg = hintfmt(
             err == SQLITE_PROTOCOL
-            ? fmt("SQLite database '%s' is busy (SQLITE_PROTOCOL)", path)
+                ? "SQLite database '%s' is busy (SQLITE_PROTOCOL)"
-            : fmt("SQLite database '%s' is busy", path));
+                : "SQLite database '%s' is busy",
-    }
+            path ? path : "(in-memory)");
-    else
+        throw exp;
-        throw SQLiteError("%s: %s (in '%s')", fs.s, sqlite3_errstr(exterr), path);
+    } else
+        throw SQLiteError(path, err, exterr, std::move(hf));
 }
 
 SQLite::SQLite(const Path & path, bool create)
@@ -37,7 +47,7 @@ SQLite::SQLite(const Path & path, bool create)
         throw Error("cannot open SQLite database '%s'", path);
 
     if (sqlite3_busy_timeout(db, 60 * 60 * 1000) != SQLITE_OK)
-        throwSQLiteError(db, "setting timeout");
+        SQLiteError::throw_(db, "setting timeout");
 
     exec("pragma foreign_keys = 1");
 }
@@ -46,7 +56,7 @@ SQLite::~SQLite()
 {
     try {
         if (db && sqlite3_close(db) != SQLITE_OK)
-            throwSQLiteError(db, "closing database");
+            SQLiteError::throw_(db, "closing database");
     } catch (...) {
         ignoreException();
     }
@@ -62,7 +72,7 @@ void SQLite::exec(const std::string & stmt)
 {
     retrySQLite<void>([&]() {
         if (sqlite3_exec(db, stmt.c_str(), 0, 0, 0) != SQLITE_OK)
-            throwSQLiteError(db, format("executing SQLite statement '%s'") % stmt);
+            SQLiteError::throw_(db, "executing SQLite statement '%s'", stmt);
     });
 }
 
@@ -76,7 +86,7 @@ void SQLiteStmt::create(sqlite3 * db, const std::string & sql)
     checkInterrupt();
     assert(!stmt);
     if (sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, 0) != SQLITE_OK)
-        throwSQLiteError(db, fmt("creating statement '%s'", sql));
+        SQLiteError::throw_(db, "creating statement '%s'", sql);
     this->db = db;
     this->sql = sql;
 }
@@ -85,7 +95,7 @@ SQLiteStmt::~SQLiteStmt()
 {
     try {
         if (stmt && sqlite3_finalize(stmt) != SQLITE_OK)
-            throwSQLiteError(db, fmt("finalizing statement '%s'", sql));
+            SQLiteError::throw_(db, "finalizing statement '%s'", sql);
     } catch (...) {
         ignoreException();
     }
@@ -109,7 +119,7 @@ SQLiteStmt::Use & SQLiteStmt::Use::operator () (std::string_view value, bool not
 {
     if (notNull) {
         if (sqlite3_bind_text(stmt, curArg++, value.data(), -1, SQLITE_TRANSIENT) != SQLITE_OK)
-            throwSQLiteError(stmt.db, "binding argument");
+            SQLiteError::throw_(stmt.db, "binding argument");
     } else
         bind();
     return *this;
@@ -119,7 +129,7 @@ SQLiteStmt::Use & SQLiteStmt::Use::operator () (const unsigned char * data, size
 {
     if (notNull) {
         if (sqlite3_bind_blob(stmt, curArg++, data, len, SQLITE_TRANSIENT) != SQLITE_OK)
-            throwSQLiteError(stmt.db, "binding argument");
+            SQLiteError::throw_(stmt.db, "binding argument");
     } else
         bind();
     return *this;
@@ -129,7 +139,7 @@ SQLiteStmt::Use & SQLiteStmt::Use::operator () (int64_t value, bool notNull)
 {
     if (notNull) {
         if (sqlite3_bind_int64(stmt, curArg++, value) != SQLITE_OK)
-            throwSQLiteError(stmt.db, "binding argument");
+            SQLiteError::throw_(stmt.db, "binding argument");
     } else
         bind();
     return *this;
@@ -138,7 +148,7 @@ SQLiteStmt::Use & SQLiteStmt::Use::operator () (int64_t value, bool notNull)
 SQLiteStmt::Use & SQLiteStmt::Use::bind()
 {
     if (sqlite3_bind_null(stmt, curArg++) != SQLITE_OK)
-        throwSQLiteError(stmt.db, "binding argument");
+        SQLiteError::throw_(stmt.db, "binding argument");
     return *this;
 }
 
@@ -152,14 +162,14 @@ void SQLiteStmt::Use::exec()
     int r = step();
     assert(r != SQLITE_ROW);
     if (r != SQLITE_DONE)
-        throwSQLiteError(stmt.db, fmt("executing SQLite statement '%s'", sqlite3_expanded_sql(stmt.stmt)));
+        SQLiteError::throw_(stmt.db, fmt("executing SQLite statement '%s'", sqlite3_expanded_sql(stmt.stmt)));
 }
 
 bool SQLiteStmt::Use::next()
 {
     int r = step();
     if (r != SQLITE_DONE && r != SQLITE_ROW)
-        throwSQLiteError(stmt.db, fmt("executing SQLite query '%s'", sqlite3_expanded_sql(stmt.stmt)));
+        SQLiteError::throw_(stmt.db, fmt("executing SQLite query '%s'", sqlite3_expanded_sql(stmt.stmt)));
     return r == SQLITE_ROW;
 }
 
@@ -185,14 +195,14 @@ SQLiteTxn::SQLiteTxn(sqlite3 * db)
 {
     this->db = db;
     if (sqlite3_exec(db, "begin;", 0, 0, 0) != SQLITE_OK)
-        throwSQLiteError(db, "starting transaction");
+        SQLiteError::throw_(db, "starting transaction");
     active = true;
 }
 
 void SQLiteTxn::commit()
 {
     if (sqlite3_exec(db, "commit;", 0, 0, 0) != SQLITE_OK)
-        throwSQLiteError(db, "committing transaction");
+        SQLiteError::throw_(db, "committing transaction");
     active = false;
 }
 
@@ -200,7 +210,7 @@ SQLiteTxn::~SQLiteTxn()
 {
     try {
         if (active && sqlite3_exec(db, "rollback;", 0, 0, 0) != SQLITE_OK)
-            throwSQLiteError(db, "aborting transaction");
+            SQLiteError::throw_(db, "aborting transaction");
     } catch (...) {
         ignoreException();
     }

src/libstore/sqlite.hh

@@ -96,10 +96,30 @@ struct SQLiteTxn
 };
 
 
-MakeError(SQLiteError, Error);
+struct SQLiteError : Error
-MakeError(SQLiteBusy, SQLiteError);
+{
+    const char *path;
+    int errNo, extendedErrNo;
 
-[[noreturn]] void throwSQLiteError(sqlite3 * db, const FormatOrString & fs);
+    template<typename... Args>
+    [[noreturn]] static void throw_(sqlite3 * db, const std::string & fs, const Args & ... args) {
+        throw_(db, hintfmt(fs, args...));
+    }
+
+    SQLiteError(const char *path, int errNo, int extendedErrNo, hintformat && hf);
+
+protected:
+
+    template<typename... Args>
+    SQLiteError(const char *path, int errNo, int extendedErrNo, const std::string & fs, const Args & ... args)
+      : SQLiteError(path, errNo, extendedErrNo, hintfmt(fs, args...))
+    { }
+
+    [[noreturn]] static void throw_(sqlite3 * db, hintformat && hf);
+
+};
+
+MakeError(SQLiteBusy, SQLiteError);
 
 void handleSQLiteBusy(const SQLiteBusy & e);
 

src/libutil/chunked-vector.hh

@@ -0,0 +1,68 @@
+#pragma once
+
+#include <bits/stdint-uintn.h>
+#include <cstdlib>
+#include <vector>
+#include <limits>
+
+namespace nix {
+
+/* Provides an indexable container like vector<> with memory overhead
+   guarantees like list<> by allocating storage in chunks of ChunkSize
+   elements instead of using a contiguous memory allocation like vector<>
+   does. Not using a single vector that is resized reduces memory overhead
+   on large data sets by on average (growth factor)/2, mostly
+   eliminates copies within the vector during resizing, and provides stable
+   references to its elements. */
+template<typename T, size_t ChunkSize>
+class ChunkedVector {
+private:
+    uint32_t size_ = 0;
+    std::vector<std::vector<T>> chunks;
+
+    /* keep this out of the ::add hot path */
+    [[gnu::noinline]]
+    auto & addChunk()
+    {
+        if (size_ >= std::numeric_limits<uint32_t>::max() - ChunkSize)
+            abort();
+        chunks.emplace_back();
+        chunks.back().reserve(ChunkSize);
+        return chunks.back();
+    }
+
+public:
+    ChunkedVector(uint32_t reserve)
+    {
+        chunks.reserve(reserve);
+        addChunk();
+    }
+
+    uint32_t size() const { return size_; }
+
+    std::pair<T &, uint32_t> add(T value)
+    {
+        const auto idx = size_++;
+        auto & chunk = [&] () -> auto & {
+            if (auto & back = chunks.back(); back.size() < ChunkSize)
+                return back;
+            return addChunk();
+        }();
+        auto & result = chunk.emplace_back(std::move(value));
+        return {result, idx};
+    }
+
+    const T & operator[](uint32_t idx) const
+    {
+        return chunks[idx / ChunkSize][idx % ChunkSize];
+    }
+
+    template<typename Fn>
+    void forEach(Fn fn) const
+    {
+        for (const auto & c : chunks)
+            for (const auto & e : c)
+                fn(e);
+    }
+};
+}

src/libutil/error.hh

@@ -87,11 +87,7 @@ struct ErrPos {
         origin = pos.origin;
         line = pos.line;
         column = pos.column;
-        // is file symbol null?
+        file = pos.file;
-        if (pos.file.set())
-            file = pos.file;
-        else
-            file = "";
         return *this;
     }
 

src/libutil/fmt.hh

@@ -2,7 +2,6 @@
 
 #include <boost/format.hpp>
 #include <string>
-#include <regex>
 #include "ansicolor.hh"
 
 
@@ -155,15 +154,4 @@ inline hintformat hintfmt(std::string plain_string)
     return hintfmt("%s", normaltxt(plain_string));
 }
 
-/* Highlight all the given matches in the given string `s` by wrapping
-   them between `prefix` and `postfix`.
-
-   If some matches overlap, then their union will be wrapped rather
-   than the individual matches. */
-std::string hiliteMatches(
-    std::string_view s,
-    std::vector<std::smatch> matches,
-    std::string_view prefix,
-    std::string_view postfix);
-
 }

src/libutil/hilite.cc

@@ -1,6 +1,4 @@
-#include "fmt.hh"
+#include "hilite.hh"
-
-#include <regex>
 
 namespace nix {
 

src/libutil/hilite.hh

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <regex>
+#include <vector>
+#include <string>
+
+namespace nix {
+
+/* Highlight all the given matches in the given string `s` by wrapping
+   them between `prefix` and `postfix`.
+
+   If some matches overlap, then their union will be wrapped rather
+   than the individual matches. */
+std::string hiliteMatches(
+    std::string_view s,
+    std::vector<std::smatch> matches,
+    std::string_view prefix,
+    std::string_view postfix);
+
+}

src/libutil/ref.hh

@@ -99,47 +99,4 @@ make_ref(Args&&... args)
     return ref<T>(p);
 }
 
-
-/* A non-nullable pointer.
-   This is similar to a C++ "& reference", but mutable.
-   This is similar to ref<T> but backed by a regular pointer instead of a smart pointer.
- */
-template<typename T>
-class ptr {
-private:
-    T * p;
-
-public:
-    ptr<T>(const ptr<T> & r)
-        : p(r.p)
-    { }
-
-    explicit ptr<T>(T * p)
-        : p(p)
-    {
-        if (!p)
-            throw std::invalid_argument("null pointer cast to ptr");
-    }
-
-    T* operator ->() const
-    {
-        return &*p;
-    }
-
-    T& operator *() const
-    {
-        return *p;
-    }
-
-    bool operator == (const ptr<T> & other) const
-    {
-        return p == other.p;
-    }
-
-    bool operator != (const ptr<T> & other) const
-    {
-        return p != other.p;
-    }
-};
-
 }

src/libutil/tests/chunked-vector.cc

@@ -0,0 +1,54 @@
+#include "chunked-vector.hh"
+
+#include <gtest/gtest.h>
+
+namespace nix {
+    TEST(ChunkedVector, InitEmpty) {
+        auto v = ChunkedVector<int, 2>(100);
+        ASSERT_EQ(v.size(), 0);
+    }
+
+    TEST(ChunkedVector, GrowsCorrectly) {
+        auto v = ChunkedVector<int, 2>(100);
+        for (auto i = 1; i < 20; i++) {
+            v.add(i);
+            ASSERT_EQ(v.size(), i);
+        }
+    }
+
+    TEST(ChunkedVector, AddAndGet) {
+        auto v = ChunkedVector<int, 2>(100);
+        for (auto i = 1; i < 20; i++) {
+            auto [i2, idx] = v.add(i);
+            auto & i3 = v[idx];
+            ASSERT_EQ(i, i2);
+            ASSERT_EQ(&i2, &i3);
+        }
+    }
+
+    TEST(ChunkedVector, ForEach) {
+        auto v = ChunkedVector<int, 2>(100);
+        for (auto i = 1; i < 20; i++) {
+            v.add(i);
+        }
+        int count = 0;
+        v.forEach([&count](int elt) {
+            count++;
+        });
+        ASSERT_EQ(count, v.size());
+    }
+
+    TEST(ChunkedVector, OverflowOK) {
+        // Similar to the AddAndGet, but intentionnally use a small
+        // initial ChunkedVector to force it to overflow
+        auto v = ChunkedVector<int, 2>(2);
+        for (auto i = 1; i < 20; i++) {
+            auto [i2, idx] = v.add(i);
+            auto & i3 = v[idx];
+            ASSERT_EQ(i, i2);
+            ASSERT_EQ(&i2, &i3);
+        }
+    }
+
+}
+

src/libutil/tests/hilite.cc

@@ -1,9 +1,7 @@
-#include "fmt.hh"
+#include "hilite.hh"
 
 #include <gtest/gtest.h>
 
-#include <regex>
-
 namespace nix {
 /* ----------- tests for fmt.hh -------------------------------------------------*/
 

src/libutil/types.hh

@@ -5,6 +5,7 @@
 #include <list>
 #include <set>
 #include <string>
+#include <limits>
 #include <map>
 #include <variant>
 #include <vector>

src/libutil/util.cc

@@ -1082,7 +1082,7 @@ std::string runProgram(Path program, bool searchPath, const Strings & args,
     auto res = runProgram(RunOptions {.program = program, .searchPath = searchPath, .args = args, .input = input});
 
     if (!statusOk(res.first))
-        throw ExecError(res.first, fmt("program '%1%' %2%", program, statusToString(res.first)));
+        throw ExecError(res.first, "program '%1%' %2%", program, statusToString(res.first));
 
     return res.second;
 }
@@ -1210,7 +1210,7 @@ void runProgram2(const RunOptions & options)
     if (source) promise.get_future().get();
 
     if (status)
-        throw ExecError(status, fmt("program '%1%' %2%", options.program, statusToString(status)));
+        throw ExecError(status, "program '%1%' %2%", options.program, statusToString(status));
 }
 
 

src/nix-env/nix-env.cc

@@ -1241,7 +1241,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                                     Attr & a(*attrs.find(i.name));
                                     if(a.value->type() != nString) continue;
                                     XMLAttrs attrs3;
-                                    attrs3["type"] = i.name;
+                                    attrs3["type"] = globals.state->symbols[i.name];
                                     attrs3["value"] = a.value->string.s;
                                     xml.writeEmptyElement("string", attrs3);
                             }

src/nix-env/user-env.cc

@@ -106,7 +106,7 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
        the store; we need it for future modifications of the
        environment. */
     std::ostringstream str;
-    manifest.print(str, true);
+    manifest.print(state.symbols, str, true);
     auto manifestFile = state.store->addTextToStore("env-manifest.nix",
         str.str(), references);
 
@@ -134,9 +134,9 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     state.forceValue(topLevel, [&]() { return topLevel.determinePos(noPos); });
     PathSet context;
     Attr & aDrvPath(*topLevel.attrs->find(state.sDrvPath));
-    auto topLevelDrv = state.coerceToStorePath(*aDrvPath.pos, *aDrvPath.value, context);
+    auto topLevelDrv = state.coerceToStorePath(aDrvPath.pos, *aDrvPath.value, context);
     Attr & aOutPath(*topLevel.attrs->find(state.sOutPath));
-    auto topLevelOut = state.coerceToStorePath(*aOutPath.pos, *aOutPath.value, context);
+    auto topLevelOut = state.coerceToStorePath(aOutPath.pos, *aOutPath.value, context);
 
     /* Realise the resulting store expression. */
     debug("building user environment");

src/nix-instantiate/nix-instantiate.cc

@@ -31,7 +31,8 @@ void processExpr(EvalState & state, const Strings & attrPaths,
     bool evalOnly, OutputKind output, bool location, Expr * e)
 {
     if (parseOnly) {
-        std::cout << format("%1%\n") % *e;
+        e->show(state.symbols, std::cout);
+        std::cout << "\n";
         return;
     }
 
@@ -55,7 +56,8 @@ void processExpr(EvalState & state, const Strings & attrPaths,
                 printValueAsJSON(state, strict, vRes, v.determinePos(noPos), std::cout, context);
             else {
                 if (strict) state.forceValueDeep(vRes);
-                std::cout << vRes << std::endl;
+                vRes.print(state.symbols, std::cout);
+                std::cout << std::endl;
             }
         } else {
             DrvInfos drvs;

src/nix/app.cc

@@ -85,9 +85,9 @@ UnresolvedApp Installable::toApp(EvalState & state)
 
     else if (type == "derivation") {
         auto drvPath = cursor->forceDerivation();
-        auto outPath = cursor->getAttr(state.sOutPath)->getString();
+        auto outPath = cursor->getAttr("outPath")->getString();
-        auto outputName = cursor->getAttr(state.sOutputName)->getString();
+        auto outputName = cursor->getAttr("outputName")->getString();
-        auto name = cursor->getAttr(state.sName)->getString();
+        auto name = cursor->getAttr("name")->getString();
         auto aPname = cursor->maybeGetAttr("pname");
         auto aMeta = cursor->maybeGetAttr("meta");
         auto aMainProgram = aMeta ? aMeta->maybeGetAttr("mainProgram") : nullptr;

src/nix/bundle.cc

@@ -97,21 +97,23 @@ struct CmdBundle : InstallableCommand
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
         PathSet context2;
-        auto drvPath = evalState->coerceToStorePath(*attr1->pos, *attr1->value, context2);
+        auto drvPath = evalState->coerceToStorePath(attr1->pos, *attr1->value, context2);
 
         auto attr2 = vRes->attrs->get(evalState->sOutPath);
         if (!attr2)
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
-        auto outPath = evalState->coerceToStorePath(*attr2->pos, *attr2->value, context2);
+        auto outPath = evalState->coerceToStorePath(attr2->pos, *attr2->value, context2);
 
         store->buildPaths({ DerivedPath::Built { drvPath } });
 
         auto outPathS = store->printStorePath(outPath);
 
         if (!outLink) {
-            auto &attr = vRes->attrs->need(evalState->sName);
+            auto * attr = vRes->attrs->get(evalState->sName);
-            outLink = evalState->forceStringNoCtx(*attr.value,*attr.pos);
+            if (!attr)
+                throw Error("attribute 'name' missing");
+            outLink = evalState->forceStringNoCtx(*attr->value, attr->pos);
         }
 
         // TODO: will crash if not a localFSStore?

src/nix/edit.cc

@@ -28,19 +28,19 @@ struct CmdEdit : InstallableCommand
     {
         auto state = getEvalState();
 
-        auto [v, pos] = installable->toValue(*state);
+        const auto [file, line] = [&] {
+            auto [v, pos] = installable->toValue(*state);
 
-        try {
+            try {
-            pos = findPackageFilename(*state, *v, installable->what());
+                return findPackageFilename(*state, *v, installable->what());
-        } catch (NoPositionInfo &) {
+            } catch (NoPositionInfo &) {
-        }
+                throw Error("cannot find position information for '%s", installable->what());
-
+            }
-        if (pos == noPos)
+        }();
-            throw Error("cannot find position information for '%s", installable->what());
 
         stopProgressBar();
 
-        auto args = editorFor(pos);
+        auto args = editorFor(file, line);
 
         restoreProcessContext();
 

src/nix/eval.cc

@@ -77,9 +77,9 @@ struct CmdEval : MixJSON, InstallableCommand
             if (pathExists(*writeTo))
                 throw Error("path '%s' already exists", *writeTo);
 
-            std::function<void(Value & v, const Pos & pos, const Path & path)> recurse;
+            std::function<void(Value & v, const PosIdx pos, const Path & path)> recurse;
 
-            recurse = [&](Value & v, const Pos & pos, const Path & path)
+            recurse = [&](Value & v, const PosIdx pos, const Path & path)
             {
                 state->forceValue(v, pos);
                 if (v.type() == nString)
@@ -88,18 +88,22 @@ struct CmdEval : MixJSON, InstallableCommand
                 else if (v.type() == nAttrs) {
                     if (mkdir(path.c_str(), 0777) == -1)
                         throw SysError("creating directory '%s'", path);
-                    for (auto & attr : *v.attrs)
+                    for (auto & attr : *v.attrs) {
+                        std::string_view name = state->symbols[attr.name];
                         try {
-                            if (attr.name == "." || attr.name == "..")
+                            if (name == "." || name == "..")
-                                throw Error("invalid file name '%s'", attr.name);
+                                throw Error("invalid file name '%s'", name);
-                            recurse(*attr.value, *attr.pos, path + "/" + std::string(attr.name));
+                            recurse(*attr.value, attr.pos, concatStrings(path, "/", name));
                         } catch (Error & e) {
-                            e.addTrace(*attr.pos, hintfmt("while evaluating the attribute '%s'", attr.name));
+                            e.addTrace(
+                                state->positions[attr.pos],
+                                hintfmt("while evaluating the attribute '%s'", name));
                             throw;
                         }
+                    }
                 }
                 else
-                    throw TypeError("value at '%s' is not a string or an attribute set", pos);
+                    throw TypeError("value at '%s' is not a string or an attribute set", state->positions[pos]);
             };
 
             recurse(*v, pos, *writeTo);
@@ -117,7 +121,7 @@ struct CmdEval : MixJSON, InstallableCommand
 
         else {
             state->forceValueDeep(*v);
-            logger->cout("%s", *v);
+            logger->cout("%s", printValue(*state, *v));
         }
     }
 };

src/nix/flake.cc

@@ -123,7 +123,7 @@ struct CmdFlakeLock : FlakeCommand
 };
 
 static void enumerateOutputs(EvalState & state, Value & vFlake,
-    std::function<void(const std::string & name, Value & vProvide, const Pos & pos)> callback)
+    std::function<void(const std::string & name, Value & vProvide, const PosIdx pos)> callback)
 {
     auto pos = vFlake.determinePos(noPos);
     state.forceAttrs(vFlake, pos);
@@ -139,11 +139,11 @@ static void enumerateOutputs(EvalState & state, Value & vFlake,
        else. This way we can disable IFD for hydraJobs and then enable
        it for other outputs. */
     if (auto attr = aOutputs->value->attrs->get(sHydraJobs))
-        callback(attr->name, *attr->value, *attr->pos);
+        callback(state.symbols[attr->name], *attr->value, attr->pos);
 
     for (auto & attr : *aOutputs->value->attrs) {
         if (attr.name != sHydraJobs)
-            callback(attr.name, *attr.value, *attr.pos);
+            callback(state.symbols[attr.name], *attr.value, attr.pos);
     }
 }
 
@@ -254,14 +254,6 @@ struct CmdFlakeInfo : CmdFlakeMetadata
     }
 };
 
-static bool argHasName(std::string_view arg, std::string_view expected)
-{
-    return
-        arg == expected
-        || arg == "_"
-        || (hasPrefix(arg, "_") && arg.substr(1) == expected);
-}
-
 struct CmdFlakeCheck : FlakeCommand
 {
     bool build = true;
@@ -315,13 +307,25 @@ struct CmdFlakeCheck : FlakeCommand
 
         // FIXME: rewrite to use EvalCache.
 
-        auto checkSystemName = [&](const std::string & system, const Pos & pos) {
+        auto resolve = [&] (PosIdx p) {
-            // FIXME: what's the format of "system"?
+            return state->positions[p];
-            if (system.find('-') == std::string::npos)
-                reportError(Error("'%s' is not a valid system type, at %s", system, pos));
         };
 
-        auto checkDerivation = [&](const std::string & attrPath, Value & v, const Pos & pos) -> std::optional<StorePath> {
+        auto argHasName = [&] (SymbolIdx arg, std::string_view expected) {
+            std::string_view name = state->symbols[arg];
+            return
+                name == expected
+                || name == "_"
+                || (hasPrefix(name, "_") && name.substr(1) == expected);
+        };
+
+        auto checkSystemName = [&](const std::string & system, const PosIdx pos) {
+            // FIXME: what's the format of "system"?
+            if (system.find('-') == std::string::npos)
+                reportError(Error("'%s' is not a valid system type, at %s", system, resolve(pos)));
+        };
+
+        auto checkDerivation = [&](const std::string & attrPath, Value & v, const PosIdx pos) -> std::optional<StorePath> {
             try {
                 auto drvInfo = getDerivation(*state, v, false);
                 if (!drvInfo)
@@ -329,7 +333,7 @@ struct CmdFlakeCheck : FlakeCommand
                 // FIXME: check meta attributes
                 return drvInfo->queryDrvPath();
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the derivation '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the derivation '%s'", attrPath));
                 reportError(e);
             }
             return std::nullopt;
@@ -337,7 +341,7 @@ struct CmdFlakeCheck : FlakeCommand
 
         std::vector<DerivedPath> drvPaths;
 
-        auto checkApp = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkApp = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 #if 0
                 // FIXME
@@ -348,12 +352,12 @@ struct CmdFlakeCheck : FlakeCommand
                 }
                 #endif
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the app definition '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the app definition '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkOverlay = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkOverlay = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 state->forceValue(v, pos);
                 if (!v.isLambda()
@@ -368,12 +372,12 @@ struct CmdFlakeCheck : FlakeCommand
                 // FIXME: if we have a 'nixpkgs' input, use it to
                 // evaluate the overlay.
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the overlay '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the overlay '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkModule = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkModule = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 state->forceValue(v, pos);
                 if (v.isLambda()) {
@@ -382,9 +386,11 @@ struct CmdFlakeCheck : FlakeCommand
                 } else if (v.type() == nAttrs) {
                     for (auto & attr : *v.attrs)
                         try {
-                            state->forceValue(*attr.value, *attr.pos);
+                            state->forceValue(*attr.value, attr.pos);
                         } catch (Error & e) {
-                            e.addTrace(*attr.pos, hintfmt("while evaluating the option '%s'", attr.name));
+                            e.addTrace(
+                                state->positions[attr.pos],
+                                hintfmt("while evaluating the option '%s'", state->symbols[attr.name]));
                             throw;
                         }
                 } else
@@ -392,14 +398,14 @@ struct CmdFlakeCheck : FlakeCommand
                 // FIXME: if we have a 'nixpkgs' input, use it to
                 // check the module.
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the NixOS module '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the NixOS module '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        std::function<void(const std::string & attrPath, Value & v, const Pos & pos)> checkHydraJobs;
+        std::function<void(const std::string & attrPath, Value & v, const PosIdx pos)> checkHydraJobs;
 
-        checkHydraJobs = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        checkHydraJobs = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 state->forceAttrs(v, pos);
 
@@ -407,23 +413,23 @@ struct CmdFlakeCheck : FlakeCommand
                     throw Error("jobset should not be a derivation at top-level");
 
                 for (auto & attr : *v.attrs) {
-                    state->forceAttrs(*attr.value, *attr.pos);
+                    state->forceAttrs(*attr.value, attr.pos);
-                    auto attrPath2 = attrPath + "." + (std::string) attr.name;
+                    auto attrPath2 = concatStrings(attrPath, ".", state->symbols[attr.name]);
                     if (state->isDerivation(*attr.value)) {
                         Activity act(*logger, lvlChatty, actUnknown,
                             fmt("checking Hydra job '%s'", attrPath2));
-                        checkDerivation(attrPath2, *attr.value, *attr.pos);
+                        checkDerivation(attrPath2, *attr.value, attr.pos);
                     } else
-                        checkHydraJobs(attrPath2, *attr.value, *attr.pos);
+                        checkHydraJobs(attrPath2, *attr.value, attr.pos);
                 }
 
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the Hydra jobset '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the Hydra jobset '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkNixOSConfiguration = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkNixOSConfiguration = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 Activity act(*logger, lvlChatty, actUnknown,
                     fmt("checking NixOS configuration '%s'", attrPath));
@@ -433,12 +439,12 @@ struct CmdFlakeCheck : FlakeCommand
                 if (!state->isDerivation(*vToplevel))
                     throw Error("attribute 'config.system.build.toplevel' is not a derivation");
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the NixOS configuration '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the NixOS configuration '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkTemplate = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkTemplate = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 Activity act(*logger, lvlChatty, actUnknown,
                     fmt("checking template '%s'", attrPath));
@@ -448,7 +454,7 @@ struct CmdFlakeCheck : FlakeCommand
                 if (auto attr = v.attrs->get(state->symbols.create("path"))) {
                     if (attr->name == state->symbols.create("path")) {
                         PathSet context;
-                        auto path = state->coerceToPath(*attr->pos, *attr->value, context);
+                        auto path = state->coerceToPath(attr->pos, *attr->value, context);
                         if (!store->isInStore(path))
                             throw Error("template '%s' has a bad 'path' attribute");
                         // TODO: recursively check the flake in 'path'.
@@ -457,29 +463,29 @@ struct CmdFlakeCheck : FlakeCommand
                     throw Error("template '%s' lacks attribute 'path'", attrPath);
 
                 if (auto attr = v.attrs->get(state->symbols.create("description")))
-                    state->forceStringNoCtx(*attr->value, *attr->pos);
+                    state->forceStringNoCtx(*attr->value, attr->pos);
                 else
                     throw Error("template '%s' lacks attribute 'description'", attrPath);
 
                 for (auto & attr : *v.attrs) {
-                    std::string name(attr.name);
+                    std::string_view name(state->symbols[attr.name]);
                     if (name != "path" && name != "description" && name != "welcomeText")
                         throw Error("template '%s' has unsupported attribute '%s'", attrPath, name);
                 }
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the template '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the template '%s'", attrPath));
                 reportError(e);
             }
         };
 
-        auto checkBundler = [&](const std::string & attrPath, Value & v, const Pos & pos) {
+        auto checkBundler = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 state->forceValue(v, pos);
                 if (!v.isLambda())
                     throw Error("bundler must be a function");
                 // TODO: check types of inputs/outputs?
             } catch (Error & e) {
-                e.addTrace(pos, hintfmt("while checking the template '%s'", attrPath));
+                e.addTrace(resolve(pos), hintfmt("while checking the template '%s'", attrPath));
                 reportError(e);
             }
         };
@@ -492,7 +498,7 @@ struct CmdFlakeCheck : FlakeCommand
 
             enumerateOutputs(*state,
                 *vFlake,
-                [&](const std::string & name, Value & vOutput, const Pos & pos) {
+                [&](const std::string & name, Value & vOutput, const PosIdx pos) {
                     Activity act(*logger, lvlChatty, actUnknown,
                         fmt("checking flake output '%s'", name));
 
@@ -516,13 +522,14 @@ struct CmdFlakeCheck : FlakeCommand
                         if (name == "checks") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
-                                state->forceAttrs(*attr.value, *attr.pos);
+                                checkSystemName(attr_name, attr.pos);
+                                state->forceAttrs(*attr.value, attr.pos);
                                 for (auto & attr2 : *attr.value->attrs) {
                                     auto drvPath = checkDerivation(
-                                        fmt("%s.%s.%s", name, attr.name, attr2.name),
+                                        fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
-                                        *attr2.value, *attr2.pos);
+                                        *attr2.value, attr2.pos);
-                                    if (drvPath && (std::string) attr.name == settings.thisSystem.get())
+                                    if (drvPath && attr_name == settings.thisSystem.get())
                                         drvPaths.push_back(DerivedPath::Built{*drvPath});
                                 }
                             }
@@ -531,61 +538,66 @@ struct CmdFlakeCheck : FlakeCommand
                         else if (name == "formatter") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
                                 checkApp(
-                                    fmt("%s.%s", name, attr.name),
+                                    fmt("%s.%s", name, attr_name),
-                                    *attr.value, *attr.pos);
+                                    *attr.value, attr.pos);
                             }
                         }
 
                         else if (name == "packages" || name == "devShells") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
-                                state->forceAttrs(*attr.value, *attr.pos);
+                                checkSystemName(attr_name, attr.pos);
+                                state->forceAttrs(*attr.value, attr.pos);
                                 for (auto & attr2 : *attr.value->attrs)
                                     checkDerivation(
-                                        fmt("%s.%s.%s", name, attr.name, attr2.name),
+                                        fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
-                                        *attr2.value, *attr2.pos);
+                                        *attr2.value, attr2.pos);
                             }
                         }
 
                         else if (name == "apps") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
-                                state->forceAttrs(*attr.value, *attr.pos);
+                                checkSystemName(attr_name, attr.pos);
+                                state->forceAttrs(*attr.value, attr.pos);
                                 for (auto & attr2 : *attr.value->attrs)
                                     checkApp(
-                                        fmt("%s.%s.%s", name, attr.name, attr2.name),
+                                        fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
-                                        *attr2.value, *attr2.pos);
+                                        *attr2.value, attr2.pos);
                             }
                         }
 
                         else if (name == "defaultPackage" || name == "devShell") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
                                 checkDerivation(
-                                    fmt("%s.%s", name, attr.name),
+                                    fmt("%s.%s", name, attr_name),
-                                    *attr.value, *attr.pos);
+                                    *attr.value, attr.pos);
                             }
                         }
 
                         else if (name == "defaultApp") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
                                 checkApp(
-                                    fmt("%s.%s", name, attr.name),
+                                    fmt("%s.%s", name, attr_name),
-                                    *attr.value, *attr.pos);
+                                    *attr.value, attr.pos);
                             }
                         }
 
                         else if (name == "legacyPackages") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                checkSystemName(state->symbols[attr.name], attr.pos);
                                 // FIXME: do getDerivations?
                             }
                         }
@@ -596,8 +608,8 @@ struct CmdFlakeCheck : FlakeCommand
                         else if (name == "overlays") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs)
-                                checkOverlay(fmt("%s.%s", name, attr.name),
+                                checkOverlay(fmt("%s.%s", name, state->symbols[attr.name]),
-                                    *attr.value, *attr.pos);
+                                    *attr.value, attr.pos);
                         }
 
                         else if (name == "nixosModule")
@@ -606,15 +618,15 @@ struct CmdFlakeCheck : FlakeCommand
                         else if (name == "nixosModules") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs)
-                                checkModule(fmt("%s.%s", name, attr.name),
+                                checkModule(fmt("%s.%s", name, state->symbols[attr.name]),
-                                    *attr.value, *attr.pos);
+                                    *attr.value, attr.pos);
                         }
 
                         else if (name == "nixosConfigurations") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs)
-                                checkNixOSConfiguration(fmt("%s.%s", name, attr.name),
+                                checkNixOSConfiguration(fmt("%s.%s", name, state->symbols[attr.name]),
-                                    *attr.value, *attr.pos);
+                                    *attr.value, attr.pos);
                         }
 
                         else if (name == "hydraJobs")
@@ -626,29 +638,31 @@ struct CmdFlakeCheck : FlakeCommand
                         else if (name == "templates") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs)
-                                checkTemplate(fmt("%s.%s", name, attr.name),
+                                checkTemplate(fmt("%s.%s", name, state->symbols[attr.name]),
-                                    *attr.value, *attr.pos);
+                                    *attr.value, attr.pos);
                         }
 
                         else if (name == "defaultBundler") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
+                                checkSystemName(attr_name, attr.pos);
                                 checkBundler(
-                                    fmt("%s.%s", name, attr.name),
+                                    fmt("%s.%s", name, attr_name),
-                                    *attr.value, *attr.pos);
+                                    *attr.value, attr.pos);
                             }
                         }
 
                         else if (name == "bundlers") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
-                                checkSystemName(attr.name, *attr.pos);
+                                const auto & attr_name = state->symbols[attr.name];
-                                state->forceAttrs(*attr.value, *attr.pos);
+                                checkSystemName(attr_name, attr.pos);
+                                state->forceAttrs(*attr.value, attr.pos);
                                 for (auto & attr2 : *attr.value->attrs) {
                                     checkBundler(
-                                        fmt("%s.%s.%s", name, attr.name, attr2.name),
+                                        fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
-                                        *attr2.value, *attr2.pos);
+                                        *attr2.value, attr2.pos);
                                 }
                             }
                         }
@@ -657,7 +671,7 @@ struct CmdFlakeCheck : FlakeCommand
                             warn("unknown flake output '%s'", name);
 
                     } catch (Error & e) {
-                        e.addTrace(pos, hintfmt("while checking flake output '%s'", name));
+                        e.addTrace(resolve(pos), hintfmt("while checking flake output '%s'", name));
                         reportError(e);
                     }
                 });
@@ -994,7 +1008,7 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
                 auto showDerivation = [&]()
                 {
-                    auto name = visitor.getAttr(state->sName)->getString();
+                    auto name = visitor.getAttr("name")->getString();
                     if (json) {
                         std::optional<std::string> description;
                         if (auto aMeta = visitor.maybeGetAttr("meta")) {

src/nix/main.cc

@@ -302,7 +302,7 @@ void mainWrapped(int argc, char * * argv)
             b["arity"] = primOp->arity;
             b["args"] = primOp->args;
             b["doc"] = trim(stripIndentation(primOp->doc));
-            res[(std::string) builtin.name] = std::move(b);
+            res[state.symbols[builtin.name]] = std::move(b);
         }
         std::cout << res.dump() << "\n";
         return;

src/nix/prefetch.cc

@@ -199,11 +199,13 @@ static int main_nix_prefetch_url(int argc, char * * argv)
             state->forceAttrs(v, noPos);
 
             /* Extract the URL. */
-            auto & attr = v.attrs->need(state->symbols.create("urls"));
+            auto * attr = v.attrs->get(state->symbols.create("urls"));
-            state->forceList(*attr.value, noPos);
+            if (!attr)
-            if (attr.value->listSize() < 1)
+                throw Error("attribute 'urls' missing");
+            state->forceList(*attr->value, noPos);
+            if (attr->value->listSize() < 1)
                 throw Error("'urls' list is empty");
-            url = state->forceString(*attr.value->listElems()[0]);
+            url = state->forceString(*attr->value->listElems()[0]);
 
             /* Extract the hash mode. */
             auto attr2 = v.attrs->get(state->symbols.create("outputHashMode"));

src/nix/repl.cc

@@ -73,7 +73,7 @@ struct NixRepl
     void initEnv();
     void reloadFiles();
     void addAttrsToScope(Value & attrs);
-    void addVarToScope(const Symbol & name, Value & v);
+    void addVarToScope(const SymbolIdx name, Value & v);
     Expr * parseString(std::string s);
     void evalString(std::string s, Value & v);
 
@@ -120,7 +120,7 @@ std::string runNix(Path program, const Strings & args,
     });
 
     if (!statusOk(res.first))
-        throw ExecError(res.first, fmt("program '%1%' %2%", program, statusToString(res.first)));
+        throw ExecError(res.first, "program '%1%' %2%", program, statusToString(res.first));
 
     return res.second;
 }
@@ -347,9 +347,9 @@ StringSet NixRepl::completePrefix(const std::string & prefix)
             state->forceAttrs(v, noPos);
 
             for (auto & i : *v.attrs) {
-                std::string name = i.name;
+                std::string_view name = state->symbols[i.name];
                 if (name.substr(0, cur2.size()) != cur2) continue;
-                completions.insert(prev + expr + "." + name);
+                completions.insert(concatStrings(prev, expr, ".", name));
             }
 
         } catch (ParseError & e) {
@@ -461,21 +461,23 @@ bool NixRepl::processLine(std::string line)
         Value v;
         evalString(arg, v);
 
-        Pos pos;
+        const auto [file, line] = [&] () -> std::pair<std::string, uint32_t> {
-
+            if (v.type() == nPath || v.type() == nString) {
-        if (v.type() == nPath || v.type() == nString) {
+                PathSet context;
-            PathSet context;
+                auto filename = state->coerceToString(noPos, v, context).toOwned();
-            auto filename = state->coerceToString(noPos, v, context);
+                state->symbols.create(filename);
-            pos.file = state->symbols.create(*filename);
+                return {filename, 0};
-        } else if (v.isLambda()) {
+            } else if (v.isLambda()) {
-            pos = v.lambda.fun->pos;
+                auto pos = state->positions[v.lambda.fun->pos];
-        } else {
+                return {pos.file, pos.line};
-            // assume it's a derivation
+            } else {
-            pos = findPackageFilename(*state, v, arg);
+                // assume it's a derivation
-        }
+                return findPackageFilename(*state, v, arg);
+            }
+        }();
 
         // Open in EDITOR
-        auto args = editorFor(pos);
+        auto args = editorFor(file, line);
         auto editor = args.front();
         args.pop_front();
 
@@ -498,7 +500,7 @@ bool NixRepl::processLine(std::string line)
         Value v, f, result;
         evalString(arg, v);
         evalString("drv: (import <nixpkgs> {}).runCommand \"shell\" { buildInputs = [ drv ]; } \"\"", f);
-        state->callFunction(f, v, result, Pos());
+        state->callFunction(f, v, result, PosIdx());
 
         StorePath drvPath = getDerivationPath(result);
         runNix("nix-shell", {state->store->printStorePath(drvPath)});
@@ -671,7 +673,7 @@ void NixRepl::initEnv()
 
     varNames.clear();
     for (auto & i : state->staticBaseEnv.vars)
-        varNames.insert(i.first);
+        varNames.emplace(state->symbols[i.first]);
 }
 
 
@@ -701,7 +703,7 @@ void NixRepl::addAttrsToScope(Value & attrs)
     for (auto & i : *attrs.attrs) {
         staticEnv.vars.emplace_back(i.name, displ);
         env->values[displ++] = i.value;
-        varNames.insert((std::string) i.name);
+        varNames.emplace(state->symbols[i.name]);
     }
     staticEnv.sort();
     staticEnv.deduplicate();
@@ -709,7 +711,7 @@ void NixRepl::addAttrsToScope(Value & attrs)
 }
 
 
-void NixRepl::addVarToScope(const Symbol & name, Value & v)
+void NixRepl::addVarToScope(const SymbolIdx name, Value & v)
 {
     if (displ >= envSize)
         throw Error("environment full; cannot add more variables");
@@ -718,7 +720,7 @@ void NixRepl::addVarToScope(const Symbol & name, Value & v)
     staticEnv.vars.emplace_back(name, displ);
     staticEnv.sort();
     env->values[displ++] = &v;
-    varNames.insert((std::string) name);
+    varNames.emplace(state->symbols[name]);
 }
 
 
@@ -799,7 +801,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
             Bindings::iterator i = v.attrs->find(state->sDrvPath);
             PathSet context;
             if (i != v.attrs->end())
-                str << state->store->printStorePath(state->coerceToStorePath(*i->pos, *i->value, context));
+                str << state->store->printStorePath(state->coerceToStorePath(i->pos, *i->value, context));
             else
                 str << "???";
             str << "»";
@@ -811,7 +813,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
             typedef std::map<std::string, Value *> Sorted;
             Sorted sorted;
             for (auto & i : *v.attrs)
-                sorted[i.name] = i.value;
+                sorted.emplace(state->symbols[i.name], i.value);
 
             for (auto & i : sorted) {
                 if (isVarName(i.first))
@@ -861,7 +863,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
     case nFunction:
         if (v.isLambda()) {
             std::ostringstream s;
-            s << v.lambda.fun->pos;
+            s << state->positions[v.lambda.fun->pos];
             str << ANSI_BLUE "«lambda @ " << filterANSIEscapes(s.str()) << "»" ANSI_NORMAL;
         } else if (v.isPrimOp()) {
             str << ANSI_MAGENTA "«primop»" ANSI_NORMAL;

src/nix/search.cc

@@ -9,7 +9,7 @@
 #include "shared.hh"
 #include "eval-cache.hh"
 #include "attr-path.hh"
-#include "fmt.hh"
+#include "hilite.hh"
 
 #include <regex>
 #include <fstream>
@@ -154,7 +154,7 @@ struct CmdSearch : InstallableCommand, MixJSON
                     recurse();
 
                 else if (attrPath[0] == "legacyPackages" && attrPath.size() > 2) {
-                    auto attr = cursor.maybeGetAttr(state->sRecurseForDerivations);
+                    auto attr = cursor.maybeGetAttr("recurseForDerivations");
                     if (attr && attr->getBool())
                         recurse();
                 }

tests/build-remote-content-addressed-floating.sh

@@ -2,7 +2,7 @@ source common.sh
 
 file=build-hook-ca-floating.nix
 
-enableFeatures "ca-derivations ca-references"
+enableFeatures "ca-derivations"
 
 CONTENT_ADDRESSED=true
 

tests/ca/common.sh

@@ -1,5 +1,5 @@
 source ../common.sh
 
-enableFeatures "ca-derivations ca-references"
+enableFeatures "ca-derivations"
 
 restartDaemon

tests/ca/selfref-gc.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+requireDaemonNewerThan "2.4pre20210626"
+
+enableFeatures "ca-derivations nix-command flakes"
+
+export NIX_TESTS_CA_BY_DEFAULT=1
+cd ..
+source ./selfref-gc.sh

tests/eval.sh

@@ -20,6 +20,8 @@ nix eval --expr 'assert 1 + 2 == 3; true'
 [[ $(nix eval attr --json -f "./eval.nix") == '{"foo":"bar"}' ]]
 [[ $(nix eval int -f - < "./eval.nix") == 123 ]]
 
+# Check if toFile can be utilized during restricted eval
+[[ $(nix eval --restrict-eval --expr 'import (builtins.toFile "source" "42")') == 42 ]]
 
 nix-instantiate --eval -E 'assert 1 + 2 == 3; true'
 [[ $(nix-instantiate -A int --eval "./eval.nix") == 123 ]]

tests/local.mk

@@ -92,6 +92,7 @@ nix_tests = \
   plugins.sh \
   build.sh \
   ca/nix-run.sh \
+  selfref-gc.sh ca/selfref-gc.sh \
   db-migration.sh \
   bash-profile.sh \
   pass-as-file.sh \

tests/nix-profile.sh

@@ -3,7 +3,7 @@ source common.sh
 clearStore
 clearProfiles
 
-enableFeatures "ca-derivations ca-references"
+enableFeatures "ca-derivations"
 restartDaemon
 
 # Make a flake.

tests/plugins/plugintest.cc

@@ -13,7 +13,7 @@ MySettings mySettings;
 
 static GlobalConfig::Register rs(&mySettings);
 
-static void prim_anotherNull (EvalState & state, const Pos & pos, Value ** args, Value & v)
+static void prim_anotherNull (EvalState & state, const PosIdx pos, Value ** args, Value & v)
 {
     if (mySettings.settingSet)
         v.mkNull();

tests/selfref-gc.sh

@@ -0,0 +1,30 @@
+source common.sh
+
+requireDaemonNewerThan "2.6.0pre20211215"
+
+clearStore
+
+nix-build --no-out-link -E '
+  with import ./config.nix;
+
+  let d1 = mkDerivation {
+    name = "selfref-gc";
+    outputs = [ "out" ];
+    buildCommand = "
+      echo SELF_REF: $out > $out
+    ";
+  }; in
+
+  # the only change from d1 is d1 as an (unused) build input
+  # to get identical store path in CA.
+  mkDerivation {
+    name = "selfref-gc";
+    outputs = [ "out" ];
+    buildCommand = "
+      echo UNUSED: ${d1}
+      echo SELF_REF: $out > $out
+    ";
+  }
+'
+
+nix-collect-garbage