From 13c4dc65327c9654c47e6d80c0f4e1797b999f97 Mon Sep 17 00:00:00 2001
From: Guillaume Maudoux <guillaume.maudoux@tweag.io>
Date: Mon, 7 Mar 2022 11:33:03 +0100
Subject: [PATCH] more fixes

---
 src/libcmd/installables.cc            |   2 +-
 src/libexpr/attr-path.cc              |   2 +-
 src/libexpr/eval-cache.cc             |   2 +-
 src/libexpr/eval-inline.hh            |   4 +-
 src/libexpr/eval.cc                   |  56 ++---
 src/libexpr/eval.hh                   |   2 +-
 src/libexpr/flake/flake.cc            |   2 +-
 src/libexpr/get-drvs.cc               |  22 +-
 src/libexpr/primops.cc                | 298 +++++++++++++-------------
 src/libexpr/primops/context.cc        |  22 +-
 src/libexpr/primops/fetchMercurial.cc |   8 +-
 src/libexpr/primops/fetchTree.cc      |  14 +-
 src/libexpr/primops/fromTOML.cc       |   2 +-
 src/nix/eval.cc                       |   2 +-
 src/nix/flake.cc                      |   4 +-
 src/nix/main.cc                       |   2 +-
 src/nix/prefetch.cc                   |  16 +-
 src/nix/repl.cc                       |   8 +-
 src/nix/upgrade-nix.cc                |   2 +-
 19 files changed, 239 insertions(+), 231 deletions(-)

diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index e85482239..437380a4d 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -524,7 +524,7 @@ ref<eval_cache::EvalCache> openEvalCache(
             auto vFlake = state.allocValue();
             flake::callFlake(state, *lockedFlake, *vFlake);
 
-            state.forceAttrs(*vFlake, noPos, "While evaluating a cached flake");
+            state.forceAttrs(*vFlake, noPos, "While evaluating a cached flake: ");
 
             auto aOutputs = vFlake->attrs->get(state.symbols.create("outputs"));
             assert(aOutputs);
diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index 63ee8b1ae..930400bd0 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -112,7 +112,7 @@ Pos findPackageFilename(EvalState & state, Value & v, std::string what)
 
     // FIXME: is it possible to extract the Pos object instead of doing this
     //        toString + parsing?
-    auto pos = state.forceString(*v2, noPos, "While evaluating the meta.position attribute of a derivation");
+    auto pos = state.forceString(*v2, noPos, "While evaluating the meta.position attribute of a derivation: ");
 
     auto colon = pos.rfind(':');
     if (colon == std::string::npos)
diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index 66078b694..6528725e7 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -336,7 +336,7 @@ Value & AttrCursor::getValue()
     if (!_value) {
         if (parent) {
             auto & vParent = parent->first->getValue();
-            root->state.forceAttrs(vParent, noPos, "While evaluating the parent attr set");
+            root->state.forceAttrs(vParent, noPos, "While evaluating the parent attr set: ");
             auto attr = vParent.attrs->get(parent->second);
             if (!attr)
                 throw Error("attribute '%s' is unexpectedly missing", getAttrPathStr());
diff --git a/src/libexpr/eval-inline.hh b/src/libexpr/eval-inline.hh
index 112c70e7b..ad53a74cb 100644
--- a/src/libexpr/eval-inline.hh
+++ b/src/libexpr/eval-inline.hh
@@ -63,7 +63,7 @@ inline void EvalState::forceAttrs(Value & v, Callable getPos, const std::string
 {
     forceValue(v, getPos);
     if (v.type() != nAttrs)
-        throwTypeError(getPos(), "%2%: value is %1% while a set was expected", v, errorCtx);
+        throwTypeError(getPos(), "%2%value is %1% while a set was expected", v, errorCtx);
 }
 
 
@@ -71,7 +71,7 @@ inline void EvalState::forceList(Value & v, const Pos & pos, const std::string &
 {
     forceValue(v, pos);
     if (!v.isList())
-        throwTypeError(pos, "%2%: value is %1% while a list was expected", v, errorCtx);
+        throwTypeError(pos, "%2%value is %1% while a list was expected", v, errorCtx);
 }
 
 /* Note: Various places expect the allocated memory to be zeroed. */
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index d3ab5ad08..55c624cb9 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -297,7 +297,7 @@ static Symbol getName(const AttrName & name, EvalState & state, Env & env)
     } else {
         Value nameValue;
         name.expr->eval(state, env, nameValue);
-        state.forceStringNoCtx(nameValue, noPos, "While evaluating an attribute name");
+        state.forceStringNoCtx(nameValue, noPos, "While evaluating an attribute name: ");
         return state.symbols.create(nameValue.string.s);
     }
 }
@@ -720,6 +720,14 @@ LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const
     });
 }
 
+LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const std::string & s2, const std::string & s3, const std::string & s4))
+{
+    throw EvalError({
+        .msg = hintfmt(s, s2, s3, s4),
+        .errPos = pos
+    });
+}
+
 LocalNoInlineNoReturn(void throwEvalError(const Pos & p1, const char * s, const Symbol & sym, const Pos & p2))
 {
     // p1 is where the error occurred; p2 is a position mentioned in the message.
@@ -1037,7 +1045,7 @@ inline bool EvalState::evalBool(Env & env, Expr * e, const Pos & pos, const std:
     Value v;
     e->eval(*this, env, v);
     if (v.type() != nBool)
-        throwTypeError(pos, "%2%: value is %1% while a Boolean was expected", v, errorCtx);
+        throwTypeError(pos, "%2%value is %1% while a Boolean was expected", v, errorCtx);
     return v.boolean;
 }
 
@@ -1046,7 +1054,7 @@ inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v, const Pos & pos
 {
     e->eval(*this, env, v);
     if (v.type() != nAttrs)
-        throwTypeError(pos, "%2%: value is %1% while a set was expected", v, errorCtx);
+        throwTypeError(pos, "%2%value is %1% while a set was expected", v, errorCtx);
 }
 
 
@@ -1119,7 +1127,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
            Hence we need __overrides.) */
         if (hasOverrides) {
             Value * vOverrides = (*v.attrs)[overrides->second.displ].value;
-            state.forceAttrs(*vOverrides, [&]() { return vOverrides->determinePos(noPos); }, "While evaluating the `__overrides` attribute");
+            state.forceAttrs(*vOverrides, [&]() { return vOverrides->determinePos(noPos); }, "While evaluating the `__overrides` attribute: ");
             Bindings * newBnds = state.allocBindings(v.attrs->capacity() + vOverrides->attrs->size());
             for (auto & i : *v.attrs)
                 newBnds->push_back(i);
@@ -1147,7 +1155,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         state.forceValue(nameVal, i.pos);
         if (nameVal.type() == nNull)
             continue;
-        state.forceStringNoCtx(nameVal, i.pos, "While evaluating the name of a dynamic attribute");
+        state.forceStringNoCtx(nameVal, i.pos, "While evaluating the name of a dynamic attribute: ");
         Symbol nameSym = state.symbols.create(nameVal.string.s);
         Bindings::iterator j = v.attrs->find(nameSym);
         if (j != v.attrs->end())
@@ -1237,7 +1245,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                     return;
                 }
             } else {
-                state.forceAttrs(*vAttrs, pos, "While selecting an attribute");
+                state.forceAttrs(*vAttrs, pos, "While selecting an attribute: ");
                 if ((j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
                     throwEvalError(pos, "attribute '%1%' missing", name);
             }
@@ -1328,7 +1336,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                 env2.values[displ++] = args[0];
 
             else {
-                forceAttrs(*args[0], pos, "While evaluating the value passed as argument to a function expecting an attribute set");
+                forceAttrs(*args[0], pos, "While evaluating the value passed as argument to a function expecting an attribute set: ");
 
                 if (!lambda.arg.empty())
                     env2.values[displ++] = args[0];
@@ -1570,7 +1578,7 @@ void ExprOpEq::eval(EvalState & state, Env & env, Value & v)
 {
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
-    v.mkBool(state.eqValues(v1, v2));
+    v.mkBool(state.eqValues(v1, v2, pos, ""));
 }
 
 
@@ -1578,7 +1586,7 @@ void ExprOpNEq::eval(EvalState & state, Env & env, Value & v)
 {
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
-    v.mkBool(!state.eqValues(v1, v2));
+    v.mkBool(!state.eqValues(v1, v2, pos, ""));
 }
 
 
@@ -1806,7 +1814,7 @@ NixInt EvalState::forceInt(Value & v, const Pos & pos, const std::string & error
 {
     forceValue(v, pos);
     if (v.type() != nInt)
-        throwTypeError(pos, "%2%: value is %1% while an integer was expected", v, errorCtx);
+        throwTypeError(pos, "%2%value is %1% while an integer was expected", v, errorCtx);
     return v.integer;
 }
 
@@ -1817,7 +1825,7 @@ NixFloat EvalState::forceFloat(Value & v, const Pos & pos, const std::string & e
     if (v.type() == nInt)
         return v.integer;
     else if (v.type() != nFloat)
-        throwTypeError(pos, "%2%: value is %1% while a float was expected", v, errorCtx);
+        throwTypeError(pos, "%2%value is %1% while a float was expected", v, errorCtx);
     return v.fpoint;
 }
 
@@ -1826,7 +1834,7 @@ bool EvalState::forceBool(Value & v, const Pos & pos, const std::string & errorC
 {
     forceValue(v, pos);
     if (v.type() != nBool)
-        throwTypeError(pos, "%2%: value is %1% while a Boolean was expected", v, errorCtx);
+        throwTypeError(pos, "%2%value is %1% while a Boolean was expected", v, errorCtx);
     return v.boolean;
 }
 
@@ -1841,7 +1849,7 @@ void EvalState::forceFunction(Value & v, const Pos & pos, const std::string & er
 {
     forceValue(v, pos);
     if (v.type() != nFunction && !isFunctor(v))
-        throwTypeError(pos, "%2%: value is %1% while a function was expected", v, errorCtx);
+        throwTypeError(pos, "%2%value is %1% while a function was expected", v, errorCtx);
 }
 
 
@@ -1849,7 +1857,7 @@ std::string_view EvalState::forceString(Value & v, const Pos & pos, const std::s
 {
     forceValue(v, pos);
     if (v.type() != nString) {
-        throwTypeError(pos, "%2%: value is %1% while a string was expected", v, errorCtx);
+        throwTypeError(pos, "%2%value is %1% while a string was expected", v, errorCtx);
     }
     return v.string.s;
 }
@@ -1958,7 +1966,7 @@ BackedStringView EvalState::coerceToString(const Pos & pos, Value & v, PathSet &
         if (maybeString)
             return std::move(*maybeString);
         auto i = v.attrs->find(sOutPath);
-        if (i == v.attrs->end()) throwTypeError(pos, "%2%: cannot coerce %1% to a string", v, errorCtx);
+        if (i == v.attrs->end()) throwTypeError(pos, "%2%cannot coerce %1% to a string", v, errorCtx);
         return coerceToString(pos, *i->value, context, coerceMore, copyToStore, canonicalizePath, errorCtx);
     }
 
@@ -1989,7 +1997,7 @@ BackedStringView EvalState::coerceToString(const Pos & pos, Value & v, PathSet &
         }
     }
 
-    throwTypeError(pos, "%2%: cannot coerce %1% to a string", v, errorCtx);
+    throwTypeError(pos, "%2%cannot coerce %1% to a string", v, errorCtx);
 }
 
 
@@ -2021,7 +2029,7 @@ Path EvalState::coerceToPath(const Pos & pos, Value & v, PathSet & context, cons
 {
     auto path = coerceToString(pos, v, context, false, false, true, errorCtx).toOwned();
     if (path == "" || path[0] != '/')
-        throwEvalError(pos, "%2%: string '%1%' doesn't represent an absolute path", path, errorCtx);
+        throwEvalError(pos, "%2%string '%1%' doesn't represent an absolute path", path, errorCtx);
     return path;
 }
 
@@ -2032,13 +2040,13 @@ StorePath EvalState::coerceToStorePath(const Pos & pos, Value & v, PathSet & con
     if (auto storePath = store->maybeParseStorePath(path))
         return *storePath;
     throw EvalError({
-        .msg = hintfmt("%2%: path '%1%' is not in the Nix store", path, errorCtx),
+        .msg = hintfmt("%2%path '%1%' is not in the Nix store", path, errorCtx),
         .errPos = pos
     });
 }
 
 
-bool EvalState::eqValues(Value & v1, Value & v2)
+bool EvalState::eqValues(Value & v1, Value & v2, const Pos & pos, const std::string & errorCtx)
 {
     forceValue(v1, noPos);
     forceValue(v2, noPos);
@@ -2077,7 +2085,7 @@ bool EvalState::eqValues(Value & v1, Value & v2)
         case nList:
             if (v1.listSize() != v2.listSize()) return false;
             for (size_t n = 0; n < v1.listSize(); ++n)
-                if (!eqValues(*v1.listElems()[n], *v2.listElems()[n])) return false;
+                if (!eqValues(*v1.listElems()[n], *v2.listElems()[n], pos, errorCtx)) return false;
             return true;
 
         case nAttrs: {
@@ -2087,7 +2095,7 @@ bool EvalState::eqValues(Value & v1, Value & v2)
                 Bindings::iterator i = v1.attrs->find(sOutPath);
                 Bindings::iterator j = v2.attrs->find(sOutPath);
                 if (i != v1.attrs->end() && j != v2.attrs->end())
-                    return eqValues(*i->value, *j->value);
+                    return eqValues(*i->value, *j->value, pos, errorCtx);
             }
 
             if (v1.attrs->size() != v2.attrs->size()) return false;
@@ -2095,7 +2103,7 @@ bool EvalState::eqValues(Value & v1, Value & v2)
             /* Otherwise, compare the attributes one by one. */
             Bindings::iterator i, j;
             for (i = v1.attrs->begin(), j = v2.attrs->begin(); i != v1.attrs->end(); ++i, ++j)
-                if (i->name != j->name || !eqValues(*i->value, *j->value))
+                if (i->name != j->name || !eqValues(*i->value, *j->value, pos, errorCtx))
                     return false;
 
             return true;
@@ -2112,7 +2120,7 @@ bool EvalState::eqValues(Value & v1, Value & v2)
             return v1.fpoint == v2.fpoint;
 
         default:
-            throwEvalError("cannot compare %1% with %2%", showType(v1), showType(v2));
+            throwEvalError(pos, "%3%cannot compare %1% with %2%", showType(v1), showType(v2), errorCtx);
     }
 }
 
@@ -2237,7 +2245,7 @@ void EvalState::printStats()
 std::string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore, const std::string & errorCtx) const
 {
     throw TypeError({
-        .msg = hintfmt("%2%: cannot coerce %1% to a string", showType(), errorCtx),
+        .msg = hintfmt("%2%cannot coerce %1% to a string", showType(), errorCtx),
         .errPos = pos
     });
 }
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index dadd46433..bd817c9fe 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -329,7 +329,7 @@ public:
 
     /* Do a deep equality test between two values.  That is, list
        elements and attributes are compared recursively. */
-    bool eqValues(Value & v1, Value & v2);
+    bool eqValues(Value & v1, Value & v2, const Pos & pos, const std::string & errorCtx);
 
     bool isFunctor(Value & fun);
 
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index fe2daaf21..560747210 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -708,7 +708,7 @@ static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Va
 {
     state.requireExperimentalFeatureOnEvaluation(Xp::Flakes, "builtins.getFlake", pos);
 
-    std::string flakeRefS(state.forceStringNoCtx(*args[0], pos, "While evaluating the argument passed to builtins.getFlake"));
+    std::string flakeRefS(state.forceStringNoCtx(*args[0], pos, "While evaluating the argument passed to builtins.getFlake: "));
     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);
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 9bb545430..94f26e925 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -50,7 +50,7 @@ std::string DrvInfo::queryName() const
     if (name == "" && attrs) {
         auto i = attrs->find(state->sName);
         if (i == attrs->end()) throw TypeError("derivation name missing");
-        name = state->forceStringNoCtx(*i->value, noPos, "While evaluating the name of a DrvInfo");
+        name = state->forceStringNoCtx(*i->value, noPos, "While evaluating the name of a DrvInfo: ");
     }
     return name;
 }
@@ -60,7 +60,7 @@ 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, "While evaluating the system of a DrvInfo");
+        system = i == attrs->end() ? "unknown" : state->forceStringNoCtx(*i->value, *i->pos, "While evaluating the system of a DrvInfo: ");
     }
     return system;
 }
@@ -74,7 +74,7 @@ std::optional<StorePath> DrvInfo::queryDrvPath() const
         if (i == attrs->end())
             drvPath = {std::nullopt};
         else
-            drvPath = {state->coerceToStorePath(*i->pos, *i->value, context, "Whyle evaluating the drv path of a DrvInfo")};
+            drvPath = {state->coerceToStorePath(*i->pos, *i->value, context, "Whyle evaluating the drv path of a DrvInfo: ")};
     }
     return drvPath.value_or(std::nullopt);
 }
@@ -94,7 +94,7 @@ 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, "While evaluating the output path of a DrvInfo");
+            outPath = state->coerceToStorePath(*i->pos, *i->value, context, "While evaluating the output path of a DrvInfo: ");
     }
     if (!outPath)
         throw UnimplementedError("CA derivations are not yet supported");
@@ -108,21 +108,21 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool onlyOutputsToInstall)
         /* Get the ‘outputs’ list. */
         Bindings::iterator i;
         if (attrs && (i = attrs->find(state->sOutputs)) != attrs->end()) {
-            state->forceList(*i->value, *i->pos, "While evaluating the outputs of a DrvInfo");
+            state->forceList(*i->value, *i->pos, "While evaluating the outputs of a DrvInfo: ");
 
             /* For each output... */
             for (auto elem : i->value->listItems()) {
                 /* Evaluate the corresponding set. */
-                std::string name(state->forceStringNoCtx(*elem, *i->pos, "While evaluating the name of one output of a DrvInfo"));
+                std::string name(state->forceStringNoCtx(*elem, *i->pos, "While evaluating the name of one output of a DrvInfo: "));
                 Bindings::iterator out = attrs->find(state->symbols.create(name));
                 if (out == attrs->end()) continue; // FIXME: throw error?
-                state->forceAttrs(*out->value, *i->pos, "While evaluating the description of a DrvInfo output");
+                state->forceAttrs(*out->value, *i->pos, "While evaluating the description of a DrvInfo output: ");
 
                 /* 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(name, state->coerceToStorePath(*outPath->pos, *outPath->value, context, "While evaluating the outPath of an output path of a DrvInfo"));
+                outputs.emplace(name, state->coerceToStorePath(*outPath->pos, *outPath->value, context, "While evaluating the outPath of an output path of a DrvInfo: "));
             }
         } else
             outputs.emplace("out", queryOutPath());
@@ -151,7 +151,7 @@ std::string DrvInfo::queryOutputName() const
 {
     if (outputName == "" && attrs) {
         Bindings::iterator i = attrs->find(state->sOutputName);
-        outputName = i != attrs->end() ? state->forceStringNoCtx(*i->value, noPos, "While evaluating the output name of a DrvInfo") : "";
+        outputName = i != attrs->end() ? state->forceStringNoCtx(*i->value, noPos, "While evaluating the output name of a DrvInfo: ") : "";
     }
     return outputName;
 }
@@ -163,7 +163,7 @@ 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, "While evaluating the `meta` attribute of a DrvInfo");
+    state->forceAttrs(*a->value, *a->pos, "While evaluating the `meta` attribute of a DrvInfo: ");
     meta = a->value->attrs;
     return meta;
 }
@@ -364,7 +364,7 @@ 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, "While evaluating the attribute `recurseForDerivations`"))
+                    if (j != i->value->attrs->end() && state.forceBool(*j->value, *j->pos, "While evaluating the attribute `recurseForDerivations`: "))
                         getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
                 }
             }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index fff382c5e..1e22044d7 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -103,7 +103,7 @@ static Path realisePath(EvalState & state, const Pos & pos, Value & v, const Rea
     auto path = [&]()
     {
         try {
-            return state.coerceToPath(pos, v, context, "While realising the context of a path");
+            return state.coerceToPath(pos, v, context, "While realising the context of a path: ");
         } catch (Error & e) {
             e.addTrace(pos, "while realising the context of a path");
             throw;
@@ -195,9 +195,9 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
                 , "/"), **state.vImportedDrvToDerivation);
         }
 
-        state.forceFunction(**state.vImportedDrvToDerivation, pos, "While evaluating imported-drv-to-derivation.nix.gen.hh");
+        state.forceFunction(**state.vImportedDrvToDerivation, pos, "While evaluating imported-drv-to-derivation.nix.gen.hh: ");
         v.mkApp(*state.vImportedDrvToDerivation, w);
-        state.forceAttrs(v, pos, "While calling imported-drv-to-derivation.nix.gen.hh");
+        state.forceAttrs(v, pos, "While calling imported-drv-to-derivation.nix.gen.hh: ");
     }
 
     else if (path == corepkgsPrefix + "fetchurl.nix") {
@@ -210,7 +210,7 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
         if (!vScope)
             state.evalFile(path, v);
         else {
-            state.forceAttrs(*vScope, pos, "While evaluating the first argument passed to builtins.scopedImport");
+            state.forceAttrs(*vScope, pos, "While evaluating the first argument passed to builtins.scopedImport: ");
 
             Env * env = &state.allocEnv(vScope->attrs->size());
             env->up = &state.baseEnv;
@@ -314,7 +314,7 @@ void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value
 {
     auto path = realisePath(state, pos, *args[0]);
 
-    std::string sym(state.forceStringNoCtx(*args[1], pos, "While evaluating the second argument passed to builtins.importNative"));
+    std::string sym(state.forceStringNoCtx(*args[1], pos, "While evaluating the second argument passed to builtins.importNative: "));
 
     void *handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL);
     if (!handle)
@@ -340,7 +340,7 @@ void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value
 /* Execute a program and parse its output */
 void prim_exec(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.exec");
+    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.exec: ");
     auto elems = args[0]->listElems();
     auto count = args[0]->listSize();
     if (count == 0) {
@@ -549,7 +549,7 @@ struct CompareValues
             return v1->integer < v2->fpoint;
         if (v1->type() != v2->type())
             throw EvalError({
-                .msg = hintfmt("%s: cannot compare %s with %s", errorCtx, showType(*v1), showType(*v2)),
+                .msg = hintfmt("%scannot compare %s with %s", errorCtx, showType(*v1), showType(*v2)),
                 .errPos = pos,
             });
         switch (v1->type()) {
@@ -568,13 +568,13 @@ struct CompareValues
                         return false;
                     } else if (i == v1->listSize()) {
                         return true;
-                    } else if (!state.eqValues(*v1->listElems()[i], *v2->listElems()[i])) {
+                    } else if (!state.eqValues(*v1->listElems()[i], *v2->listElems()[i], pos, errorCtx)) {
                         return (*this)(v1->listElems()[i], v2->listElems()[i]);
                     }
                 }
             default:
                 throw EvalError({
-                    .msg = hintfmt("%s: cannot compare %s with %s", errorCtx, showType(*v1), showType(*v2)),
+                    .msg = hintfmt("%scannot compare %s with %s", errorCtx, showType(*v1), showType(*v2)),
                     .errPos = pos,
                 });
         }
@@ -628,7 +628,7 @@ static Bindings::iterator getAttr(
 
 static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0], pos, "While evaluating the first argument passed to builtins.genericClosure");
+    state.forceAttrs(*args[0], pos, "While evaluating the first argument passed to builtins.genericClosure: ");
 
     /* Get the start set. */
     Bindings::iterator startSet = getAttr(
@@ -639,7 +639,7 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         pos
     );
 
-    state.forceList(*startSet->value, pos, "While evaluating the `startSet` attribute passed to builtins.genericClosure");
+    state.forceList(*startSet->value, pos, "While evaluating the `startSet` attribute passed to builtins.genericClosure: ");
 
     ValueList workSet;
     for (auto elem : startSet->value->listItems())
@@ -654,7 +654,7 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         pos
     );
 
-    state.forceFunction(*op->value, pos, "While evaluating the `operator` attribute passed to builtins.genericClosure");
+    state.forceFunction(*op->value, pos, "While evaluating the `operator` attribute passed to builtins.genericClosure: ");
 
     /* Construct the closure by applying the operator to element of
        `workSet', adding the result to `workSet', continuing until
@@ -668,7 +668,7 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         Value * e = *(workSet.begin());
         workSet.pop_front();
 
-        state.forceAttrs(*e, pos, "While evaluating one item to be part of the genericClosure");
+        state.forceAttrs(*e, pos, "While evaluating one item to be part of the genericClosure: ");
 
         Bindings::iterator key =
             e->attrs->find(state.sKey);
@@ -685,7 +685,7 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         /* Call the `operator' function with `e' as argument. */
         Value res;
         state.callFunction(*op->value, 1, &e, res, pos);
-        state.forceList(res, pos, "While evaluating the return value of the `operator` passed to builtins.genericClosure");
+        state.forceList(res, pos, "While evaluating the return value of the `operator` passed to builtins.genericClosure: ");
 
         /* Add the values returned by the operator to the work set. */
         for (auto elem : res.listItems()) {
@@ -782,7 +782,7 @@ static RegisterPrimOp primop_ceil({
 
 static void prim_floor(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto value = state.forceFloat(*args[0], args[0]->determinePos(pos), "While evaluating the first argument passed to builtins.floor");
+    auto value = state.forceFloat(*args[0], args[0]->determinePos(pos), "While evaluating the first argument passed to builtins.floor: ");
     v.mkInt(floor(value));
 }
 
@@ -839,7 +839,7 @@ static RegisterPrimOp primop_tryEval({
 /* Return an environment variable.  Use with care. */
 static void prim_getEnv(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    std::string name(state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.getEnv"));
+    std::string name(state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.getEnv: "));
     v.mkString(evalSettings.restrictEval || evalSettings.pureEval ? "" : getEnv(name).value_or(""));
 }
 
@@ -937,7 +937,7 @@ static RegisterPrimOp primop_trace({
    derivation. */
 static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.derivationStrict");
+    state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.derivationStrict: ");
 
     /* Figure out the name first (for stack backtraces). */
     Bindings::iterator attr = getAttr(
@@ -951,7 +951,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
     std::string drvName;
     Pos & posDrvName(*attr->pos);
     try {
-        drvName = state.forceStringNoCtx(*attr->value, pos, "While evaluating the `name` attribute passed to builtins.derivationStrict");
+        drvName = state.forceStringNoCtx(*attr->value, pos, "While evaluating the `name` attribute passed to builtins.derivationStrict: ");
     } catch (Error & e) {
         e.addTrace(posDrvName, "while evaluating the derivation attribute 'name'");
         throw;
@@ -961,14 +961,14 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
     std::ostringstream jsonBuf;
     std::unique_ptr<JSONObject> jsonObject;
     attr = args[0]->attrs->find(state.sStructuredAttrs);
-    if (attr != args[0]->attrs->end() && state.forceBool(*attr->value, pos, "While evaluating the `__structuredAttrs` attribute passed to builtins.derivationStrict"))
+    if (attr != args[0]->attrs->end() && state.forceBool(*attr->value, pos, "While evaluating the `__structuredAttrs` attribute passed to builtins.derivationStrict: "))
         jsonObject = std::make_unique<JSONObject>(jsonBuf);
 
     /* Check whether null attributes should be ignored. */
     bool ignoreNulls = false;
     attr = args[0]->attrs->find(state.sIgnoreNulls);
     if (attr != args[0]->attrs->end())
-        ignoreNulls = state.forceBool(*attr->value, pos, "While evaluating the `__ignoreNulls` attribute passed to builtins.derivationStrict");
+        ignoreNulls = state.forceBool(*attr->value, pos, "While evaluating the `__ignoreNulls` attribute passed to builtins.derivationStrict: ");
 
     /* Build the derivation expression by processing the attributes. */
     Derivation drv;
@@ -1064,26 +1064,26 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
                     printValueAsJSON(state, true, *i->value, pos, placeholder, context);
 
                     if (i->name == state.sBuilder)
-                        drv.builder = state.forceString(*i->value, context, posDrvName, "While evaluating the `builder` attribute passed to builtins.derivationStrict");
+                        drv.builder = state.forceString(*i->value, context, posDrvName, "While evaluating the `builder` attribute passed to builtins.derivationStrict: ");
                     else if (i->name == state.sSystem)
-                        drv.platform = state.forceStringNoCtx(*i->value, posDrvName, "While evaluating the `system` attribute passed to builtins.derivationStrict");
+                        drv.platform = state.forceStringNoCtx(*i->value, posDrvName, "While evaluating the `system` attribute passed to builtins.derivationStrict: ");
                     else if (i->name == state.sOutputHash)
-                        outputHash = state.forceStringNoCtx(*i->value, posDrvName, "While evaluating the `outputHash` attribute passed to builtins.derivationStrict");
+                        outputHash = state.forceStringNoCtx(*i->value, posDrvName, "While evaluating the `outputHash` attribute passed to builtins.derivationStrict: ");
                     else if (i->name == state.sOutputHashAlgo)
-                        outputHashAlgo = state.forceStringNoCtx(*i->value, posDrvName, "While evaluating the `outputHashAlgo` attribute passed to builtins.derivationStrict");
+                        outputHashAlgo = state.forceStringNoCtx(*i->value, posDrvName, "While evaluating the `outputHashAlgo` attribute passed to builtins.derivationStrict: ");
                     else if (i->name == state.sOutputHashMode)
-                        handleHashMode(state.forceStringNoCtx(*i->value, posDrvName, "While evaluating the `outputHashMode` attribute passed to builtins.derivationStrict"));
+                        handleHashMode(state.forceStringNoCtx(*i->value, posDrvName, "While evaluating the `outputHashMode` attribute passed to builtins.derivationStrict: "));
                     else if (i->name == state.sOutputs) {
                         /* Require ‘outputs’ to be a list of strings. */
-                        state.forceList(*i->value, posDrvName, "While evaluating the `outputs` attribute passed to builtins.derivationStrict");
+                        state.forceList(*i->value, posDrvName, "While evaluating the `outputs` attribute passed to builtins.derivationStrict: ");
                         Strings ss;
                         for (auto elem : i->value->listItems())
-                            ss.emplace_back(state.forceStringNoCtx(*elem, posDrvName, "While evaluating an element of the `outputs` attribute passed to builtins.derivationStrict"));
+                            ss.emplace_back(state.forceStringNoCtx(*elem, posDrvName, "While evaluating an element of the `outputs` attribute passed to builtins.derivationStrict: "));
                         handleOutputs(ss);
                     }
 
                 } else {
-                    auto s = state.coerceToString(*i->pos, *i->value, context, true, "While evaluating an attribute passed to builtins.derivationStrict").toOwned();
+                    auto s = state.coerceToString(*i->pos, *i->value, context, true, "While evaluating an attribute passed to builtins.derivationStrict: ").toOwned();
                     drv.env.emplace(key, s);
                     if (i->name == state.sBuilder) drv.builder = std::move(s);
                     else if (i->name == state.sSystem) drv.platform = std::move(s);
@@ -1291,7 +1291,7 @@ static RegisterPrimOp primop_derivationStrict(RegisterPrimOp::Info {
    ‘out’. */
 static void prim_placeholder(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    v.mkString(hashPlaceholder(state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.placeholder")));
+    v.mkString(hashPlaceholder(state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.placeholder: ")));
 }
 
 static RegisterPrimOp primop_placeholder({
@@ -1315,7 +1315,7 @@ static RegisterPrimOp primop_placeholder({
 static void prim_toPath(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    Path path = state.coerceToPath(pos, *args[0], context, "While evaluating the first argument passed to builtins.toPath");
+    Path path = state.coerceToPath(pos, *args[0], context, "While evaluating the first argument passed to builtins.toPath: ");
     v.mkString(canonPath(path), context);
 }
 
@@ -1346,7 +1346,7 @@ static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, V
         });
 
     PathSet context;
-    Path path = state.checkSourcePath(state.coerceToPath(pos, *args[0], context, "While evaluating the first argument passed to builtins.storePath"));
+    Path path = state.checkSourcePath(state.coerceToPath(pos, *args[0], context, "While evaluating the first argument passed to builtins.storePath: "));
     /* Resolve symlinks in ‘path’, unless ‘path’ itself is a symlink
        directly in the store.  The latter condition is necessary so
        e.g. nix-push does the right thing. */
@@ -1416,7 +1416,7 @@ static RegisterPrimOp primop_pathExists({
 static void prim_baseNameOf(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    v.mkString(baseNameOf(*state.coerceToString(pos, *args[0], context, false, false, "While evaluating the first argument passed to builtins.baseNameOf")), context);
+    v.mkString(baseNameOf(*state.coerceToString(pos, *args[0], context, false, false, "While evaluating the first argument passed to builtins.baseNameOf: ")), context);
 }
 
 static RegisterPrimOp primop_baseNameOf({
@@ -1436,7 +1436,7 @@ static RegisterPrimOp primop_baseNameOf({
 static void prim_dirOf(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto path = state.coerceToString(pos, *args[0], context, false, false, "While evaluating the first argument passed to builtins.dirOf");
+    auto path = state.coerceToString(pos, *args[0], context, false, false, "While evaluating the first argument passed to builtins.dirOf: ");
     auto dir = dirOf(*path);
     if (args[0]->type() == nPath) v.mkPath(dir); else v.mkString(dir, context);
 }
@@ -1483,17 +1483,17 @@ static RegisterPrimOp primop_readFile({
    which are desugared to 'findFile __nixPath "x"'. */
 static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.findFile");
+    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.findFile: ");
 
     SearchPath searchPath;
 
     for (auto v2 : args[0]->listItems()) {
-        state.forceAttrs(*v2, pos, "While evaluating an element of the list passed to builtins.findFile");
+        state.forceAttrs(*v2, pos, "While evaluating an element of the list passed to builtins.findFile: ");
 
         std::string prefix;
         Bindings::iterator i = v2->attrs->find(state.sPrefix);
         if (i != v2->attrs->end())
-            prefix = state.forceStringNoCtx(*i->value, pos, "While evaluating the `prefix` attribute of an element of the list passed to builtins.findFile");
+            prefix = state.forceStringNoCtx(*i->value, pos, "While evaluating the `prefix` attribute of an element of the list passed to builtins.findFile: ");
 
         i = getAttr(
             state,
@@ -1521,7 +1521,7 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
         searchPath.emplace_back(prefix, path);
     }
 
-    auto path = state.forceStringNoCtx(*args[1], pos, "While evaluating the second argument passed to builtins.findFile");
+    auto path = state.forceStringNoCtx(*args[1], pos, "While evaluating the second argument passed to builtins.findFile: ");
 
     v.mkPath(state.checkSourcePath(state.findFile(searchPath, path, pos)));
 }
@@ -1535,7 +1535,7 @@ static RegisterPrimOp primop_findFile(RegisterPrimOp::Info {
 /* Return the cryptographic hash of a file in base-16. */
 static void prim_hashFile(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto type = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.hashFile");
+    auto type = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.hashFile: ");
     std::optional<HashType> ht = parseHashType(type);
     if (!ht)
         throw Error({
@@ -1742,7 +1742,7 @@ static RegisterPrimOp primop_toJSON({
 /* Parse a JSON string to a value. */
 static void prim_fromJSON(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto s = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.fromJSON");
+    auto s = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.fromJSON: ");
     try {
         parseJSON(state, s, v);
     } catch (JSONParseError &e) {
@@ -1771,8 +1771,8 @@ static RegisterPrimOp primop_fromJSON({
 static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    std::string name(state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.toFile"));
-    std::string contents(state.forceString(*args[1], context, pos, "While evaluating the second argument passed to builtins.toFile"));
+    std::string name(state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.toFile: "));
+    std::string contents(state.forceString(*args[1], context, pos, "While evaluating the second argument passed to builtins.toFile: "));
 
     StorePathSet refs;
 
@@ -1929,7 +1929,7 @@ static void addPath(
             Value res;
             state.callFunction(*filterFun, 2, args, res, pos);
 
-            return state.forceBool(res, pos, "While evaluating the return value of the path filter function");
+            return state.forceBool(res, pos, "While evaluating the return value of the path filter function: ");
         }) : defaultPathFilter;
 
         std::optional<StorePath> expectedStorePath;
@@ -1955,9 +1955,9 @@ static void addPath(
 static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    Path path = state.coerceToPath(pos, *args[1], context, "While evaluating the second argument (the path to filter) passed to builtins.filterSource");
+    Path path = state.coerceToPath(pos, *args[1], context, "While evaluating the second argument (the path to filter) passed to builtins.filterSource: ");
 
-    state.forceFunction(*args[0], pos, "While evaluating the first argument to builtins.filterSource");
+    state.forceFunction(*args[0], pos, "While evaluating the first argument to builtins.filterSource: ");
     addPath(state, pos, std::string(baseNameOf(path)), path, args[0], FileIngestionMethod::Recursive, std::nullopt, v, context);
 }
 
@@ -2018,7 +2018,7 @@ static RegisterPrimOp primop_filterSource({
 
 static void prim_path(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.path");
+    state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.path: ");
     Path path;
     std::string name;
     Value * filterFun = nullptr;
@@ -2029,15 +2029,15 @@ static void prim_path(EvalState & state, const Pos & pos, Value * * args, Value
     for (auto & attr : *args[0]->attrs) {
         auto & n(attr.name);
         if (n == "path")
-            path = state.coerceToPath(*attr.pos, *attr.value, context, "While evaluating the `path` attribute passed to builtins.path");
+            path = state.coerceToPath(*attr.pos, *attr.value, context, "While evaluating the `path` attribute passed to builtins.path: ");
         else if (attr.name == state.sName)
-            name = state.forceStringNoCtx(*attr.value, *attr.pos, "while evaluating the `name` attribute passed to builtins.path");
+            name = state.forceStringNoCtx(*attr.value, *attr.pos, "while evaluating the `name` attribute passed to builtins.path: ");
         else if (n == "filter")
-            state.forceFunction(*(filterFun = attr.value), *attr.pos, "While evaluating the `filter` parameter passed to builtins.path");
+            state.forceFunction(*(filterFun = attr.value), *attr.pos, "While evaluating the `filter` parameter passed to builtins.path: ");
         else if (n == "recursive")
-            method = FileIngestionMethod { state.forceBool(*attr.value, *attr.pos, "While evaluating the `recursive` attribute passed to builtins.path") };
+            method = FileIngestionMethod { state.forceBool(*attr.value, *attr.pos, "While evaluating the `recursive` attribute passed to builtins.path: ") };
         else if (n == "sha256")
-            expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the `sha256` attribute passed to builtins.path"), htSHA256);
+            expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the `sha256` attribute passed to builtins.path: "), htSHA256);
         else
             throw EvalError({
                 .msg = hintfmt("unsupported argument '%1%' to 'addPath'", attr.name),
@@ -2100,7 +2100,7 @@ static RegisterPrimOp primop_path({
    strings. */
 static void prim_attrNames(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.attrNames");
+    state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.attrNames: ");
 
     state.mkList(v, args[0]->attrs->size());
 
@@ -2127,7 +2127,7 @@ static RegisterPrimOp primop_attrNames({
    order as attrNames. */
 static void prim_attrValues(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.attrValues");
+    state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.attrValues: ");
 
     state.mkList(v, args[0]->attrs->size());
 
@@ -2158,8 +2158,8 @@ static RegisterPrimOp primop_attrValues({
 /* Dynamic version of the `.' operator. */
 void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto attr = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.getAttr");
-    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.getAttr");
+    auto attr = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.getAttr: ");
+    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.getAttr: ");
     Bindings::iterator i = getAttr(
         state,
         "getAttr",
@@ -2188,8 +2188,8 @@ static RegisterPrimOp primop_getAttr({
 /* Return position information of the specified attribute. */
 static void prim_unsafeGetAttrPos(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto attr = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.unsafeGetAttrPos");
-    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.unsafeGetAttrPos");
+    auto attr = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.unsafeGetAttrPos: ");
+    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.unsafeGetAttrPos: ");
     Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
     if (i == args[1]->attrs->end())
         v.mkNull();
@@ -2206,8 +2206,8 @@ static RegisterPrimOp primop_unsafeGetAttrPos(RegisterPrimOp::Info {
 /* Dynamic version of the `?' operator. */
 static void prim_hasAttr(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto attr = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.hasAttr");
-    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.hasAttr");
+    auto attr = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.hasAttr: ");
+    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.hasAttr: ");
     v.mkBool(args[1]->attrs->find(state.symbols.create(attr)) != args[1]->attrs->end());
 }
 
@@ -2240,8 +2240,8 @@ static RegisterPrimOp primop_isAttrs({
 
 static void prim_removeAttrs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0], pos, "While evaluating the first argument passed to builtins.removeAttrs");
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.removeAttrs");
+    state.forceAttrs(*args[0], pos, "While evaluating the first argument passed to builtins.removeAttrs: ");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.removeAttrs: ");
 
     /* Get the attribute names to be removed.
        We keep them as Attrs instead of Symbols so std::set_difference
@@ -2249,7 +2249,7 @@ static void prim_removeAttrs(EvalState & state, const Pos & pos, Value * * args,
     boost::container::small_vector<Attr, 64> names;
     names.reserve(args[1]->listSize());
     for (auto elem : args[1]->listItems()) {
-        state.forceStringNoCtx(*elem, pos, "While evaluating the values of the second argument passed to builtins.removeAttrs");
+        state.forceStringNoCtx(*elem, pos, "While evaluating the values of the second argument passed to builtins.removeAttrs: ");
         names.emplace_back(state.symbols.create(elem->string.s), nullptr);
     }
     std::sort(names.begin(), names.end());
@@ -2288,14 +2288,14 @@ static RegisterPrimOp primop_removeAttrs({
    name, the first takes precedence. */
 static void prim_listToAttrs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[0], pos, "While evaluating the argument passed to builtins.listToAttrs");
+    state.forceList(*args[0], pos, "While evaluating the argument passed to builtins.listToAttrs: ");
 
     auto attrs = state.buildBindings(args[0]->listSize());
 
     std::set<Symbol> seen;
 
     for (auto v2 : args[0]->listItems()) {
-        state.forceAttrs(*v2, pos, "While evaluating an element of the list passed to builtins.listToAttrs");
+        state.forceAttrs(*v2, pos, "While evaluating an element of the list passed to builtins.listToAttrs: ");
 
         Bindings::iterator j = getAttr(
             state,
@@ -2305,7 +2305,7 @@ static void prim_listToAttrs(EvalState & state, const Pos & pos, Value * * args,
             pos
         );
 
-        auto name = state.forceStringNoCtx(*j->value, *j->pos, "While evaluating the `name` attribute of an element of the list passed to builtins.listToAttrs");
+        auto name = state.forceStringNoCtx(*j->value, *j->pos, "While evaluating the `name` attribute of an element of the list passed to builtins.listToAttrs: ");
 
         Symbol sym = state.symbols.create(name);
         if (seen.insert(sym).second) {
@@ -2350,8 +2350,8 @@ static RegisterPrimOp primop_listToAttrs({
 
 static void prim_intersectAttrs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0], pos, "While evaluating the first argument passed to builtins.intersectAttrs");
-    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.intersectAttrs");
+    state.forceAttrs(*args[0], pos, "While evaluating the first argument passed to builtins.intersectAttrs: ");
+    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.intersectAttrs: ");
 
     auto attrs = state.buildBindings(std::min(args[0]->attrs->size(), args[1]->attrs->size()));
 
@@ -2376,14 +2376,14 @@ static RegisterPrimOp primop_intersectAttrs({
 
 static void prim_catAttrs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    Symbol attrName = state.symbols.create(state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.catAttrs"));
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.catAttrs");
+    Symbol attrName = state.symbols.create(state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.catAttrs: "));
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.catAttrs: ");
 
     Value * res[args[1]->listSize()];
     unsigned int found = 0;
 
     for (auto v2 : args[1]->listItems()) {
-        state.forceAttrs(*v2, pos, "While evaluating an element in the list passed as second argument to builtins.catAttrs");
+        state.forceAttrs(*v2, pos, "While evaluating an element in the list passed as second argument to builtins.catAttrs: ");
         Bindings::iterator i = v2->attrs->find(attrName);
         if (i != v2->attrs->end())
             res[found++] = i->value;
@@ -2456,7 +2456,7 @@ static RegisterPrimOp primop_functionArgs({
 /*  */
 static void prim_mapAttrs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.mapAttrs");
+    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.mapAttrs: ");
 
     auto attrs = state.buildBindings(args[1]->attrs->size());
 
@@ -2497,15 +2497,15 @@ static void prim_zipAttrsWith(EvalState & state, const Pos & pos, Value * * args
 
     std::map<Symbol, std::pair<size_t, Value * *>> attrsSeen;
 
-    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.zipAttrsWith");
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.zipAttrsWith");
+    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.zipAttrsWith: ");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.zipAttrsWith: ");
     const auto listSize = args[1]->listSize();
     const auto listElems = args[1]->listElems();
 
     for (unsigned int n = 0; n < listSize; ++n) {
         Value * vElem = listElems[n];
         try {
-            state.forceAttrs(*vElem, noPos, "While evaluating a value of the list passed as second argument to builtins.zipAttrsWith");
+            state.forceAttrs(*vElem, noPos, "While evaluating a value of the list passed as second argument to builtins.zipAttrsWith: ");
             for (auto & attr : *vElem->attrs)
                 attrsSeen[attr.name].first++;
         } catch (TypeError & e) {
@@ -2595,7 +2595,7 @@ static RegisterPrimOp primop_isList({
 
 static void elemAt(EvalState & state, const Pos & pos, Value & list, int n, Value & v)
 {
-    state.forceList(list, pos, "While evaluating the first argument passed to builtins.elemAt");
+    state.forceList(list, pos, "While evaluating the first argument passed to builtins.elemAt: ");
     if (n < 0 || (unsigned int) n >= list.listSize())
         throw Error({
             .msg = hintfmt("list index %1% is out of bounds", n),
@@ -2608,7 +2608,7 @@ static void elemAt(EvalState & state, const Pos & pos, Value & list, int n, Valu
 /* Return the n-1'th element of a list. */
 static void prim_elemAt(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    elemAt(state, pos, *args[0], state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.elemAt"), v);
+    elemAt(state, pos, *args[0], state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.elemAt: "), v);
 }
 
 static RegisterPrimOp primop_elemAt({
@@ -2643,7 +2643,7 @@ static RegisterPrimOp primop_head({
    don't want to use it!  */
 static void prim_tail(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.tail");
+    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.tail: ");
     if (args[0]->listSize() == 0)
         throw Error({
             .msg = hintfmt("'tail' called on an empty list"),
@@ -2674,12 +2674,12 @@ static RegisterPrimOp primop_tail({
 /* Apply a function to every element of a list. */
 static void prim_map(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.map");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.map: ");
 
     state.mkList(v, args[1]->listSize());
 
     if (args[1]->listSize() > 0) {
-        state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.map");
+        state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.map: ");
 
         for (unsigned int n = 0; n < v.listSize(); ++n)
             (v.listElems()[n] = state.allocValue())->mkApp(
@@ -2708,14 +2708,14 @@ static RegisterPrimOp primop_map({
    returns true. */
 static void prim_filter(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.filter");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.filter: ");
 
     if (args[1]->listSize() == 0) {
         v = *args[1];
         return;
     }
 
-    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.filter");
+    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.filter: ");
 
     // FIXME: putting this on the stack is risky.
     Value * vs[args[1]->listSize()];
@@ -2725,7 +2725,7 @@ static void prim_filter(EvalState & state, const Pos & pos, Value * * args, Valu
     for (unsigned int n = 0; n < args[1]->listSize(); ++n) {
         Value res;
         state.callFunction(*args[0], *args[1]->listElems()[n], res, noPos);
-        if (state.forceBool(res, pos, "While evaluating the return value of the filtering function passed to builtins.filter"))
+        if (state.forceBool(res, pos, "While evaluating the return value of the filtering function passed to builtins.filter: "))
             vs[k++] = args[1]->listElems()[n];
         else
             same = false;
@@ -2753,9 +2753,9 @@ static RegisterPrimOp primop_filter({
 static void prim_elem(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     bool res = false;
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.elem");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.elem: ");
     for (auto elem : args[1]->listItems())
-        if (state.eqValues(*args[0], *elem)) {
+        if (state.eqValues(*args[0], *elem, pos, "While searching for the presence of the given element in the list: ")) {
             res = true;
             break;
         }
@@ -2775,7 +2775,7 @@ static RegisterPrimOp primop_elem({
 /* Concatenate a list of lists. */
 static void prim_concatLists(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.concatLists");
+    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.concatLists: ");
     state.concatLists(v, args[0]->listSize(), args[0]->listElems(), pos, "While evaluating a value of the list passed to builtins.concatLists");
 }
 
@@ -2791,7 +2791,7 @@ static RegisterPrimOp primop_concatLists({
 /* Return the length of a list.  This is an O(1) time operation. */
 static void prim_length(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.length");
+    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.length: ");
     v.mkInt(args[0]->listSize());
 }
 
@@ -2808,8 +2808,8 @@ static RegisterPrimOp primop_length({
    right. The operator is applied strictly. */
 static void prim_foldlStrict(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.foldlStrict");
-    state.forceList(*args[2], pos, "While evaluating the third argument passed to builtins.foldlStrict");
+    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.foldlStrict: ");
+    state.forceList(*args[2], pos, "While evaluating the third argument passed to builtins.foldlStrict: ");
 
     if (args[2]->listSize()) {
         Value * vCur = args[1];
@@ -2841,13 +2841,13 @@ static RegisterPrimOp primop_foldlStrict({
 
 static void anyOrAll(bool any, EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceFunction(*args[0], pos, std::string("While evaluating the first argument passed to builtins.") + (any ? "any" : "all"));
-    state.forceList(*args[1], pos, std::string("While evaluating the second argument passed to builtins.") + (any ? "any" : "all"));
+    state.forceFunction(*args[0], pos, std::string("While evaluating the first argument passed to builtins.: ") + (any ? "any" : "all: "));
+    state.forceList(*args[1], pos, std::string("While evaluating the second argument passed to builtins.: ") + (any ? "any" : "all"));
 
     Value vTmp;
     for (auto elem : args[1]->listItems()) {
         state.callFunction(*args[0], *elem, vTmp, pos);
-        bool res = state.forceBool(vTmp, pos, std::string("While evaluating the return value of the function passed to builtins.") + (any ? "any" : "all"));
+        bool res = state.forceBool(vTmp, pos, std::string("While evaluating the return value of the function passed to builtins.: ") + (any ? "any" : "all"));
         if (res == any) {
             v.mkBool(any);
             return;
@@ -2890,7 +2890,7 @@ static RegisterPrimOp primop_all({
 
 static void prim_genList(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto len = state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.genList");
+    auto len = state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.genList: ");
 
     if (len < 0)
         throw EvalError({
@@ -2928,7 +2928,7 @@ static void prim_lessThan(EvalState & state, const Pos & pos, Value * * args, Va
 
 static void prim_sort(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.sort");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.sort: ");
 
     auto len = args[1]->listSize();
     if (len == 0) {
@@ -2936,7 +2936,7 @@ static void prim_sort(EvalState & state, const Pos & pos, Value * * args, Value
         return;
     }
 
-    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.sort");
+    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.sort: ");
 
     state.mkList(v, len);
     for (unsigned int n = 0; n < len; ++n) {
@@ -2948,12 +2948,12 @@ static void prim_sort(EvalState & state, const Pos & pos, Value * * args, Value
         /* Optimization: if the comparator is lessThan, bypass
            callFunction. */
         if (args[0]->isPrimOp() && args[0]->primOp->fun == prim_lessThan)
-            return CompareValues(state, pos, "While evaluating the ordering function passed to builtins.sort")(a, b);
+            return CompareValues(state, pos, "While evaluating the ordering function passed to builtins.sort: ")(a, b);
 
         Value * vs[] = {a, b};
         Value vBool;
         state.callFunction(*args[0], 2, vs, vBool, pos);
-        return state.forceBool(vBool, pos, "While evaluating the return value of the sorting function passed to builtins.sort");
+        return state.forceBool(vBool, pos, "While evaluating the return value of the sorting function passed to builtins.sort: ");
     };
 
     /* FIXME: std::sort can segfault if the comparator is not a strict
@@ -2985,8 +2985,8 @@ static RegisterPrimOp primop_sort({
 
 static void prim_partition(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.partition");
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.partition");
+    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.partition: ");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.partition: ");
 
     auto len = args[1]->listSize();
 
@@ -2997,7 +2997,7 @@ static void prim_partition(EvalState & state, const Pos & pos, Value * * args, V
         state.forceValue(*vElem, pos);
         Value res;
         state.callFunction(*args[0], *vElem, res, pos);
-        if (state.forceBool(res, pos, "While evaluating the return value of the partition function passed to builtins.partition"))
+        if (state.forceBool(res, pos, "While evaluating the return value of the partition function passed to builtins.partition: "))
             right.push_back(vElem);
         else
             wrong.push_back(vElem);
@@ -3045,15 +3045,15 @@ static RegisterPrimOp primop_partition({
 
 static void prim_groupBy(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.groupBy");
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.groupBy");
+    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.groupBy: ");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.groupBy: ");
 
     ValueVectorMap attrs;
 
     for (auto vElem : args[1]->listItems()) {
         Value res;
         state.callFunction(*args[0], *vElem, res, pos);
-        auto name = state.forceStringNoCtx(res, pos, "While evaluating the return value of the grouping function passed to builtins.groupBy");
+        auto name = state.forceStringNoCtx(res, pos, "While evaluating the return value of the grouping function passed to builtins.groupBy: ");
         Symbol sym = state.symbols.create(name);
         auto vector = attrs.try_emplace(sym, ValueVector()).first;
         vector->second.push_back(vElem);
@@ -3097,8 +3097,8 @@ static RegisterPrimOp primop_groupBy({
 
 static void prim_concatMap(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.concatMap");
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.concatMap");
+    state.forceFunction(*args[0], pos, "While evaluating the first argument passed to builtins.concatMap: ");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.concatMap: ");
     auto nrLists = args[1]->listSize();
 
     Value lists[nrLists];
@@ -3108,7 +3108,7 @@ static void prim_concatMap(EvalState & state, const Pos & pos, Value * * args, V
         Value * vElem = args[1]->listElems()[n];
         state.callFunction(*args[0], *vElem, lists[n], pos);
         try {
-            state.forceList(lists[n], lists[n].determinePos(args[0]->determinePos(pos)), "While evaluating the return value of the function passed to buitlins.concatMap");
+            state.forceList(lists[n], lists[n].determinePos(args[0]->determinePos(pos)), "While evaluating the return value of the function passed to buitlins.concatMap: ");
         } catch (TypeError &e) {
             e.addTrace(pos, hintfmt("while invoking '%s'", "concatMap"));
             throw;
@@ -3147,11 +3147,11 @@ static void prim_add(EvalState & state, const Pos & pos, Value * * args, Value &
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
     if (args[0]->type() == nFloat || args[1]->type() == nFloat)
-        v.mkFloat(state.forceFloat(*args[0], pos, "While evaluating the first argument of the addition")
-                + state.forceFloat(*args[1], pos, "While evaluating the second argument of the addition"));
+        v.mkFloat(state.forceFloat(*args[0], pos, "While evaluating the first argument of the addition: ")
+                + state.forceFloat(*args[1], pos, "While evaluating the second argument of the addition: "));
     else
-        v.mkInt(  state.forceInt(*args[0], pos, "While evaluating the first argument of the addition")
-                + state.forceInt(*args[1], pos, "While evaluating the second argument of the addition"));
+        v.mkInt(  state.forceInt(*args[0], pos, "While evaluating the first argument of the addition: ")
+                + state.forceInt(*args[1], pos, "While evaluating the second argument of the addition: "));
 }
 
 static RegisterPrimOp primop_add({
@@ -3168,11 +3168,11 @@ static void prim_sub(EvalState & state, const Pos & pos, Value * * args, Value &
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
     if (args[0]->type() == nFloat || args[1]->type() == nFloat)
-        v.mkFloat(state.forceFloat(*args[0], pos, "While evaluating the first argument of the subtraction")
-                - state.forceFloat(*args[1], pos, "While evaluating the second argument of the subtraction"));
+        v.mkFloat(state.forceFloat(*args[0], pos, "While evaluating the first argument of the subtraction: ")
+                - state.forceFloat(*args[1], pos, "While evaluating the second argument of the subtraction: "));
     else
-        v.mkInt(  state.forceInt(*args[0], pos, "While evaluating the first argument of the subtraction")
-                - state.forceInt(*args[1], pos, "While evaluating the second argument of the subtraction"));
+        v.mkInt(  state.forceInt(*args[0], pos, "While evaluating the first argument of the subtraction: ")
+                - state.forceInt(*args[1], pos, "While evaluating the second argument of the subtraction: "));
 }
 
 static RegisterPrimOp primop_sub({
@@ -3189,11 +3189,11 @@ static void prim_mul(EvalState & state, const Pos & pos, Value * * args, Value &
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
     if (args[0]->type() == nFloat || args[1]->type() == nFloat)
-        v.mkFloat(state.forceFloat(*args[0], pos, "While evaluating the first of the multiplication")
-                * state.forceFloat(*args[1], pos, "While evaluating the second argument of the multiplication"));
+        v.mkFloat(state.forceFloat(*args[0], pos, "While evaluating the first of the multiplication: ")
+                * state.forceFloat(*args[1], pos, "While evaluating the second argument of the multiplication: "));
     else
-        v.mkInt(  state.forceInt(*args[0], pos, "While evaluating the first argument of the multiplication")
-                * state.forceInt(*args[1], pos, "While evaluating the second argument of the multiplication"));
+        v.mkInt(  state.forceInt(*args[0], pos, "While evaluating the first argument of the multiplication: ")
+                * state.forceInt(*args[1], pos, "While evaluating the second argument of the multiplication: "));
 }
 
 static RegisterPrimOp primop_mul({
@@ -3210,7 +3210,7 @@ static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value &
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
 
-    NixFloat f2 = state.forceFloat(*args[1], pos, "While evaluating the second operand of the division");
+    NixFloat f2 = state.forceFloat(*args[1], pos, "While evaluating the second operand of the division: ");
     if (f2 == 0)
         throw EvalError({
             .msg = hintfmt("division by zero"),
@@ -3218,10 +3218,10 @@ static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value &
         });
 
     if (args[0]->type() == nFloat || args[1]->type() == nFloat) {
-        v.mkFloat(state.forceFloat(*args[0], pos, "While evaluating the first operand of the division") / f2);
+        v.mkFloat(state.forceFloat(*args[0], pos, "While evaluating the first operand of the division: ") / f2);
     } else {
-        NixInt i1 = state.forceInt(*args[0], pos, "While evaluating the first operand of the division");
-        NixInt i2 = state.forceInt(*args[1], pos, "While evaluating the second operand of the division");
+        NixInt i1 = state.forceInt(*args[0], pos, "While evaluating the first operand of the division: ");
+        NixInt i2 = state.forceInt(*args[1], pos, "While evaluating the second operand of the division: ");
         /* Avoid division overflow as it might raise SIGFPE. */
         if (i1 == std::numeric_limits<NixInt>::min() && i2 == -1)
             throw EvalError({
@@ -3244,8 +3244,8 @@ static RegisterPrimOp primop_div({
 
 static void prim_bitAnd(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    v.mkInt(state.forceInt(*args[0], pos, "While evaluating the first argument passed to builtins.bitAnd")
-            & state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.bitAnd"));
+    v.mkInt(state.forceInt(*args[0], pos, "While evaluating the first argument passed to builtins.bitAnd: ")
+            & state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.bitAnd: "));
 }
 
 static RegisterPrimOp primop_bitAnd({
@@ -3259,8 +3259,8 @@ static RegisterPrimOp primop_bitAnd({
 
 static void prim_bitOr(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    v.mkInt(state.forceInt(*args[0], pos, "While evaluating the first argument passed to builtins.bitOr")
-            | state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.bitOr"));
+    v.mkInt(state.forceInt(*args[0], pos, "While evaluating the first argument passed to builtins.bitOr: ")
+            | state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.bitOr: "));
 }
 
 static RegisterPrimOp primop_bitOr({
@@ -3274,8 +3274,8 @@ static RegisterPrimOp primop_bitOr({
 
 static void prim_bitXor(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    v.mkInt(state.forceInt(*args[0], pos, "While evaluating the first argument passed to builtins.bitXor")
-            ^ state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.bitXor"));
+    v.mkInt(state.forceInt(*args[0], pos, "While evaluating the first argument passed to builtins.bitXor: ")
+            ^ state.forceInt(*args[1], pos, "While evaluating the second argument passed to builtins.bitXor: "));
 }
 
 static RegisterPrimOp primop_bitXor({
@@ -3319,7 +3319,7 @@ static RegisterPrimOp primop_lessThan({
 static void prim_toString(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto s = state.coerceToString(pos, *args[0], context, true, false, "While evaluating the first argument passed to builtins.toString");
+    auto s = state.coerceToString(pos, *args[0], context, true, false, "While evaluating the first argument passed to builtins.toString: ");
     v.mkString(*s, context);
 }
 
@@ -3353,10 +3353,10 @@ static RegisterPrimOp primop_toString({
    non-negative. */
 static void prim_substring(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    int start = state.forceInt(*args[0], pos, "While evaluating the first argument (the start offset) passed to builtins.substring");
-    int len = state.forceInt(*args[1], pos, "While evaluating the second argument (the substring length) passed to builtins.substring");
+    int start = state.forceInt(*args[0], pos, "While evaluating the first argument (the start offset) passed to builtins.substring: ");
+    int len = state.forceInt(*args[1], pos, "While evaluating the second argument (the substring length) passed to builtins.substring: ");
     PathSet context;
-    auto s = state.coerceToString(pos, *args[2], context, "While evaluating the third argument (the string) passed to builtins.substring");
+    auto s = state.coerceToString(pos, *args[2], context, "While evaluating the third argument (the string) passed to builtins.substring: ");
 
     if (start < 0)
         throw EvalError({
@@ -3390,7 +3390,7 @@ static RegisterPrimOp primop_substring({
 static void prim_stringLength(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto s = state.coerceToString(pos, *args[0], context, "While evaluating the argument passed to builtins.stringLength");
+    auto s = state.coerceToString(pos, *args[0], context, "While evaluating the argument passed to builtins.stringLength: ");
     v.mkInt(s->size());
 }
 
@@ -3407,7 +3407,7 @@ static RegisterPrimOp primop_stringLength({
 /* Return the cryptographic hash of a string in base-16. */
 static void prim_hashString(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto type = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.hashString");
+    auto type = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.hashString: ");
     std::optional<HashType> ht = parseHashType(type);
     if (!ht)
         throw Error({
@@ -3416,7 +3416,7 @@ static void prim_hashString(EvalState & state, const Pos & pos, Value * * args,
         });
 
     PathSet context; // discarded
-    auto s = state.forceString(*args[1], context, pos, "While evaluating the second argument passed to builtins.hashString");
+    auto s = state.forceString(*args[1], context, pos, "While evaluating the second argument passed to builtins.hashString: ");
 
     v.mkString(hashString(*ht, s).to_string(Base16, false));
 }
@@ -3455,14 +3455,14 @@ std::shared_ptr<RegexCache> makeRegexCache()
 
 void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto re = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.match");
+    auto re = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.match: ");
 
     try {
 
         auto regex = state.regexCache->get(re);
 
         PathSet context;
-        const auto str = state.forceString(*args[1], context, pos, "While evaluating the second argument passed to builtins.match");
+        const auto str = state.forceString(*args[1], context, pos, "While evaluating the second argument passed to builtins.match: ");
 
         std::cmatch match;
         if (!std::regex_match(str.begin(), str.end(), match, regex)) {
@@ -3536,14 +3536,14 @@ static RegisterPrimOp primop_match({
    non-matching parts interleaved by the lists of the matching groups. */
 void prim_split(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto re = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.split");
+    auto re = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.split: ");
 
     try {
 
         auto regex = state.regexCache->get(re);
 
         PathSet context;
-        const auto str = state.forceString(*args[1], context, pos, "While evaluating the second argument passed to builtins.split");
+        const auto str = state.forceString(*args[1], context, pos, "While evaluating the second argument passed to builtins.split: ");
 
         auto begin = std::cregex_iterator(str.begin(), str.end(), regex);
         auto end = std::cregex_iterator();
@@ -3642,8 +3642,8 @@ static void prim_concatStringsSep(EvalState & state, const Pos & pos, Value * *
 {
     PathSet context;
 
-    auto sep = state.forceString(*args[0], context, pos, "While evaluating the first argument (the separator string) passed to builtins.concatStringsSep");
-    state.forceList(*args[1], pos, "While evaluating the second argument (the list of strings to concat) passed to builtins.concatStringsSep");
+    auto sep = state.forceString(*args[0], context, pos, "While evaluating the first argument (the separator string) passed to builtins.concatStringsSep: ");
+    state.forceList(*args[1], pos, "While evaluating the second argument (the list of strings to concat) passed to builtins.concatStringsSep: ");
 
     std::string res;
     res.reserve((args[1]->listSize() + 32) * sep.size());
@@ -3651,7 +3651,7 @@ static void prim_concatStringsSep(EvalState & state, const Pos & pos, Value * *
 
     for (auto elem : args[1]->listItems()) {
         if (first) first = false; else res += sep;
-        res += *state.coerceToString(pos, *elem, context, "While evaluating one element of the list of strings to concat passed to builtins.concatStringsSep");
+        res += *state.coerceToString(pos, *elem, context, "While evaluating one element of the list of strings to concat passed to builtins.concatStringsSep: ");
     }
 
     v.mkString(res, context);
@@ -3670,8 +3670,8 @@ static RegisterPrimOp primop_concatStringsSep({
 
 static void prim_replaceStrings(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.replaceStrings");
-    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.replaceStrings");
+    state.forceList(*args[0], pos, "While evaluating the first argument passed to builtins.replaceStrings: ");
+    state.forceList(*args[1], pos, "While evaluating the second argument passed to builtins.replaceStrings: ");
     if (args[0]->listSize() != args[1]->listSize())
         throw EvalError({
             .msg = hintfmt("'from' and 'to' arguments to 'replaceStrings' have different lengths"),
@@ -3681,18 +3681,18 @@ static void prim_replaceStrings(EvalState & state, const Pos & pos, Value * * ar
     std::vector<std::string> from;
     from.reserve(args[0]->listSize());
     for (auto elem : args[0]->listItems())
-        from.emplace_back(state.forceString(*elem, pos, "While evaluating one of the strings to replace in builtins.replaceStrings"));
+        from.emplace_back(state.forceString(*elem, pos, "While evaluating one of the strings to replace in builtins.replaceStrings: "));
 
     std::vector<std::pair<std::string, PathSet>> to;
     to.reserve(args[1]->listSize());
     for (auto elem : args[1]->listItems()) {
         PathSet ctx;
-        auto s = state.forceString(*elem, ctx, pos, "While evaluating one of the replacement strings of builtins.replaceStrings");
+        auto s = state.forceString(*elem, ctx, pos, "While evaluating one of the replacement strings of builtins.replaceStrings: ");
         to.emplace_back(s, std::move(ctx));
     }
 
     PathSet context;
-    auto s = state.forceString(*args[2], context, pos, "While evaluating the third argument passed to builtins.replaceStrings");
+    auto s = state.forceString(*args[2], context, pos, "While evaluating the third argument passed to builtins.replaceStrings: ");
 
     std::string res;
     // Loops one past last character to handle the case where 'from' contains an empty string.
@@ -3750,7 +3750,7 @@ static RegisterPrimOp primop_replaceStrings({
 
 static void prim_parseDrvName(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto name = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.parseDrvName");
+    auto name = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.parseDrvName: ");
     DrvName parsed(name);
     auto attrs = state.buildBindings(2);
     attrs.alloc(state.sName).mkString(parsed.name);
@@ -3774,8 +3774,8 @@ static RegisterPrimOp primop_parseDrvName({
 
 static void prim_compareVersions(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto version1 = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.compareVersions");
-    auto version2 = state.forceStringNoCtx(*args[1], pos, "While evaluating the second argument passed to builtins.compareVersions");
+    auto version1 = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.compareVersions: ");
+    auto version2 = state.forceStringNoCtx(*args[1], pos, "While evaluating the second argument passed to builtins.compareVersions: ");
     v.mkInt(compareVersions(version1, version2));
 }
 
@@ -3794,7 +3794,7 @@ static RegisterPrimOp primop_compareVersions({
 
 static void prim_splitVersion(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    auto version = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.splitVersion");
+    auto version = state.forceStringNoCtx(*args[0], pos, "While evaluating the first argument passed to builtins.splitVersion: ");
     auto iter = version.cbegin();
     Strings components;
     while (iter != version.cend()) {
diff --git a/src/libexpr/primops/context.cc b/src/libexpr/primops/context.cc
index 78320dc09..222d183e4 100644
--- a/src/libexpr/primops/context.cc
+++ b/src/libexpr/primops/context.cc
@@ -7,7 +7,7 @@ namespace nix {
 static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto s = state.coerceToString(pos, *args[0], context, "While evaluating the argument passed to builtins.unsafeDiscardStringContext");
+    auto s = state.coerceToString(pos, *args[0], context, "While evaluating the argument passed to builtins.unsafeDiscardStringContext: ");
     v.mkString(*s);
 }
 
@@ -17,7 +17,7 @@ static RegisterPrimOp primop_unsafeDiscardStringContext("__unsafeDiscardStringCo
 static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    state.forceString(*args[0], context, pos, "While evaluating the argument passed to builtins.hasContext");
+    state.forceString(*args[0], context, pos, "While evaluating the argument passed to builtins.hasContext: ");
     v.mkBool(!context.empty());
 }
 
@@ -33,7 +33,7 @@ static RegisterPrimOp primop_hasContext("__hasContext", 1, prim_hasContext);
 static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto s = state.coerceToString(pos, *args[0], context, "While evaluating the argument passed to builtins.unsafeDiscardOutputDependency");
+    auto s = state.coerceToString(pos, *args[0], context, "While evaluating the argument passed to builtins.unsafeDiscardOutputDependency: ");
 
     PathSet context2;
     for (auto & p : context)
@@ -72,7 +72,7 @@ static void prim_getContext(EvalState & state, const Pos & pos, Value * * args,
         Strings outputs;
     };
     PathSet context;
-    state.forceString(*args[0], context, pos, "While evaluating the argument passed to builtins.getContext");
+    state.forceString(*args[0], context, pos, "While evaluating the argument passed to builtins.getContext: ");
     auto contextInfos = std::map<Path, ContextInfo>();
     for (const auto & p : context) {
         Path drv;
@@ -136,9 +136,9 @@ static RegisterPrimOp primop_getContext("__getContext", 1, prim_getContext);
 static void prim_appendContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto orig = state.forceString(*args[0], context, pos, "while evaluating the first argument passed to builtins.appendContext");
+    auto orig = state.forceString(*args[0], context, pos, "while evaluating the first argument passed to builtins.appendContext: ");
 
-    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.appendContext");
+    state.forceAttrs(*args[1], pos, "While evaluating the second argument passed to builtins.appendContext: ");
 
     auto sPath = state.symbols.create("path");
     auto sAllOutputs = state.symbols.create("allOutputs");
@@ -150,16 +150,16 @@ static void prim_appendContext(EvalState & state, const Pos & pos, Value * * arg
             });
         if (!settings.readOnlyMode)
             state.store->ensurePath(state.store->parseStorePath(i.name));
-        state.forceAttrs(*i.value, *i.pos, "While evaluating the value of a string context");
+        state.forceAttrs(*i.value, *i.pos, "While evaluating the value of a string context: ");
         auto iter = i.value->attrs->find(sPath);
         if (iter != i.value->attrs->end()) {
-            if (state.forceBool(*iter->value, *iter->pos, "While evaluating the `path` attribute of a string context"))
+            if (state.forceBool(*iter->value, *iter->pos, "While evaluating the `path` attribute of a string context: "))
                 context.insert(i.name);
         }
 
         iter = i.value->attrs->find(sAllOutputs);
         if (iter != i.value->attrs->end()) {
-            if (state.forceBool(*iter->value, *iter->pos, "While evaluating the `allOutputs` attribute of a string context")) {
+            if (state.forceBool(*iter->value, *iter->pos, "While evaluating the `allOutputs` attribute of a string context: ")) {
                 if (!isDerivation(i.name)) {
                     throw EvalError({
                         .msg = hintfmt("Tried to add all-outputs context of %s, which is not a derivation, to a string", i.name),
@@ -172,7 +172,7 @@ static void prim_appendContext(EvalState & state, const Pos & pos, Value * * arg
 
         iter = i.value->attrs->find(state.sOutputs);
         if (iter != i.value->attrs->end()) {
-            state.forceList(*iter->value, *iter->pos, "While evaluating the `outputs` attribute of a string context");
+            state.forceList(*iter->value, *iter->pos, "While evaluating the `outputs` attribute of a string context: ");
             if (iter->value->listSize() && !isDerivation(i.name)) {
                 throw EvalError({
                     .msg = hintfmt("Tried to add derivation output context of %s, which is not a derivation, to a string", i.name),
@@ -180,7 +180,7 @@ static void prim_appendContext(EvalState & state, const Pos & pos, Value * * arg
                 });
             }
             for (auto elem : iter->value->listItems()) {
-                auto name = state.forceStringNoCtx(*elem, *iter->pos, "While evaluating an output name within a string context");
+                auto name = state.forceStringNoCtx(*elem, *iter->pos, "While evaluating an output name within a string context: ");
                 context.insert(concatStrings("!", name, "!", i.name));
             }
         }
diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index dcaf3d362..7434b8101 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -22,18 +22,18 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
         for (auto & attr : *args[0]->attrs) {
             std::string_view n(attr.name);
             if (n == "url")
-                url = state.coerceToString(*attr.pos, *attr.value, context, false, false, "While evaluating the `url` attribute passed to builtins.fetchMercurial").toOwned();
+                url = state.coerceToString(*attr.pos, *attr.value, context, false, false, "While evaluating the `url` attribute passed to builtins.fetchMercurial: ").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, "While evaluating the `rev` attribute passed to builtins.fetchMercurial");
+                auto value = state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the `rev` attribute passed to builtins.fetchMercurial: ");
                 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, "While evaluating the `name` attribute passed to builtins.fetchMercurial");
+                name = state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the `name` attribute passed to builtins.fetchMercurial: ");
             else
                 throw EvalError({
                     .msg = hintfmt("unsupported argument '%s' to 'fetchMercurial'", attr.name),
@@ -48,7 +48,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
             });
 
     } else
-        url = state.coerceToString(pos, *args[0], context, false, false, "While evaluating the first argument passed to builtins.fetchMercurial").toOwned();
+        url = state.coerceToString(pos, *args[0], context, false, false, "While evaluating the first argument passed to builtins.fetchMercurial: ").toOwned();
 
     // FIXME: git externals probably can be used to bypass the URI
     // whitelist. Ah well.
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index 2baa272cb..31a8907f1 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -102,7 +102,7 @@ static void fetchTree(
     state.forceValue(*args[0], pos);
 
     if (args[0]->type() == nAttrs) {
-        state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.fetchTree");
+        state.forceAttrs(*args[0], pos, "While evaluating the argument passed to builtins.fetchTree: ");
 
         fetchers::Attrs attrs;
 
@@ -112,7 +112,7 @@ static void fetchTree(
                     .msg = hintfmt("unexpected attribute 'type'"),
                     .errPos = pos
                 });
-            type = state.forceStringNoCtx(*aType->value, *aType->pos, "While evaluating the `type` attribute passed to builtins.fetchTree");
+            type = state.forceStringNoCtx(*aType->value, *aType->pos, "While evaluating the `type` attribute passed to builtins.fetchTree: ");
         } else if (!type)
             throw Error({
                 .msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
@@ -151,7 +151,7 @@ static void fetchTree(
 
         input = fetchers::Input::fromAttrs(std::move(attrs));
     } else {
-        auto url = state.coerceToString(pos, *args[0], context, false, false, "While evaluating the first argument passed to the fetcher").toOwned();
+        auto url = state.coerceToString(pos, *args[0], context, false, false, "While evaluating the first argument passed to the fetcher: ").toOwned();
 
         if (type == "git") {
             fetchers::Attrs attrs;
@@ -198,11 +198,11 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
         for (auto & attr : *args[0]->attrs) {
             std::string n(attr.name);
             if (n == "url")
-                url = state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the url we should fetch");
+                url = state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the url we should fetch: ");
             else if (n == "sha256")
-                expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the sha256 of the content we should fetch"), htSHA256);
+                expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the sha256 of the content we should fetch: "), htSHA256);
             else if (n == "name")
-                name = state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the name of the content we should fetch");
+                name = state.forceStringNoCtx(*attr.value, *attr.pos, "While evaluating the name of the content we should fetch: ");
             else
                 throw EvalError({
                     .msg = hintfmt("unsupported argument '%s' to '%s'", attr.name, who),
@@ -216,7 +216,7 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
                 .errPos = pos
             });
     } else
-        url = state.forceStringNoCtx(*args[0], pos, "While evaluating the url we should fetch");
+        url = state.forceStringNoCtx(*args[0], pos, "While evaluating the url we should fetch: ");
 
     url = resolveUri(*url);
 
diff --git a/src/libexpr/primops/fromTOML.cc b/src/libexpr/primops/fromTOML.cc
index 6bfd8e285..2a038bb20 100644
--- a/src/libexpr/primops/fromTOML.cc
+++ b/src/libexpr/primops/fromTOML.cc
@@ -7,7 +7,7 @@ namespace nix {
 
 static void prim_fromTOML(EvalState & state, const Pos & pos, Value * * args, Value & val)
 {
-    auto toml = state.forceStringNoCtx(*args[0], pos, "While evaluating the argument passed to builtins.fromTOML");
+    auto toml = state.forceStringNoCtx(*args[0], pos, "While evaluating the argument passed to builtins.fromTOML: ");
 
     std::istringstream tomlStream(std::string{toml});
 
diff --git a/src/nix/eval.cc b/src/nix/eval.cc
index 8ee3ba45b..1d66d457c 100644
--- a/src/nix/eval.cc
+++ b/src/nix/eval.cc
@@ -107,7 +107,7 @@ struct CmdEval : MixJSON, InstallableCommand
 
         else if (raw) {
             stopProgressBar();
-            std::cout << *state->coerceToString(noPos, *v, context, "While generating the eval command output");
+            std::cout << *state->coerceToString(noPos, *v, context, "While generating the eval command output: ");
         }
 
         else if (json) {
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 356f89713..9ba6e5be1 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -126,12 +126,12 @@ static void enumerateOutputs(EvalState & state, Value & vFlake,
     std::function<void(const std::string & name, Value & vProvide, const Pos & pos)> callback)
 {
     auto pos = vFlake.determinePos(noPos);
-    state.forceAttrs(vFlake, pos, "While evaluating a flake to get its outputs");
+    state.forceAttrs(vFlake, pos, "While evaluating a flake to get its outputs: ");
 
     auto aOutputs = vFlake.attrs->get(state.symbols.create("outputs"));
     assert(aOutputs);
 
-    state.forceAttrs(*aOutputs->value, pos, "While evaluating the outputs of a flake");
+    state.forceAttrs(*aOutputs->value, pos, "While evaluating the outputs of a flake: ");
 
     auto sHydraJobs = state.symbols.create("hydraJobs");
 
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 0c6286686..3ba7ce8b6 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -196,7 +196,7 @@ static void showHelp(std::vector<std::string> subcommand, MultiCommand & topleve
     if (!attr)
         throw UsageError("Nix has no subcommand '%s'", concatStringsSep("", subcommand));
 
-    auto markdown = state.forceString(*attr->value, noPos, "While evaluating the lowdown help text");
+    auto markdown = state.forceString(*attr->value, noPos, "While evaluating the lowdown help text: ");
 
     RunPager pager;
     std::cout << renderMarkdownToTerminal(markdown) << "\n";
diff --git a/src/nix/prefetch.cc b/src/nix/prefetch.cc
index 4376da896..a4a8ab605 100644
--- a/src/nix/prefetch.cc
+++ b/src/nix/prefetch.cc
@@ -28,17 +28,17 @@ std::string resolveMirrorUrl(EvalState & state, const std::string & url)
     Value vMirrors;
     // FIXME: use nixpkgs flake
     state.eval(state.parseExprFromString("import <nixpkgs/pkgs/build-support/fetchurl/mirrors.nix>", "."), vMirrors);
-    state.forceAttrs(vMirrors, noPos, "While evaluating the set of all mirrors");
+    state.forceAttrs(vMirrors, noPos, "While evaluating the set of all mirrors: ");
 
     auto mirrorList = vMirrors.attrs->find(state.symbols.create(mirrorName));
     if (mirrorList == vMirrors.attrs->end())
         throw Error("unknown mirror name '%s'", mirrorName);
-    state.forceList(*mirrorList->value, noPos, "While evaluating this mirror configuration");
+    state.forceList(*mirrorList->value, noPos, "While evaluating this mirror configuration: ");
 
     if (mirrorList->value->listSize() < 1)
         throw Error("mirror URL '%s' did not expand to anything", url);
 
-    std::string mirror(state.forceString(*mirrorList->value->listElems()[0], noPos, "While evaluating the first available mirror"));
+    std::string mirror(state.forceString(*mirrorList->value->listElems()[0], noPos, "While evaluating the first available mirror: "));
     return mirror + (hasSuffix(mirror, "/") ? "" : "/") + s.substr(p + 1);
 }
 
@@ -196,27 +196,27 @@ static int main_nix_prefetch_url(int argc, char * * argv)
             Value vRoot;
             state->evalFile(path, vRoot);
             Value & v(*findAlongAttrPath(*state, attrPath, autoArgs, vRoot).first);
-            state->forceAttrs(v, noPos, "While evaluating the source attribute to prefetch");
+            state->forceAttrs(v, noPos, "While evaluating the source attribute to prefetch: ");
 
             /* Extract the URL. */
             auto & attr = v.attrs->need(state->symbols.create("urls"));
-            state->forceList(*attr.value, noPos, "While evaluating the urls to prefetch");
+            state->forceList(*attr.value, noPos, "While evaluating the urls to prefetch: ");
             if (attr.value->listSize() < 1)
                 throw Error("'urls' list is empty");
-            url = state->forceString(*attr.value->listElems()[0], noPos, "While evaluating the first url from the urls list");
+            url = state->forceString(*attr.value->listElems()[0], noPos, "While evaluating the first url from the urls list: ");
 
             /* Extract the hash mode. */
             auto attr2 = v.attrs->get(state->symbols.create("outputHashMode"));
             if (!attr2)
                 printInfo("warning: this does not look like a fetchurl call");
             else
-                unpack = state->forceString(*attr2->value, noPos, "While evaluating the outputHashMode of the source to prefetch") == "recursive";
+                unpack = state->forceString(*attr2->value, noPos, "While evaluating the outputHashMode of the source to prefetch: ") == "recursive";
 
             /* Extract the name. */
             if (!name) {
                 auto attr3 = v.attrs->get(state->symbols.create("name"));
                 if (!attr3)
-                    name = state->forceString(*attr3->value, noPos, "While evaluating the name of the source to prefetch");
+                    name = state->forceString(*attr3->value, noPos, "While evaluating the name of the source to prefetch: ");
             }
         }
 
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
index 0cb68552c..038ed4911 100644
--- a/src/nix/repl.cc
+++ b/src/nix/repl.cc
@@ -342,7 +342,7 @@ StringSet NixRepl::completePrefix(const std::string & prefix)
             Expr * e = parseString(expr);
             Value v;
             e->eval(*state, *env, v);
-            state->forceAttrs(v, noPos, "nevermind, it is ignored anyway");
+            state->forceAttrs(v, noPos, "nevermind, it is ignored anyway: ");
 
             for (auto & i : *v.attrs) {
                 std::string name = i.name;
@@ -461,7 +461,7 @@ bool NixRepl::processLine(std::string line)
 
         if (v.type() == nPath || v.type() == nString) {
             PathSet context;
-            auto filename = state->coerceToString(noPos, v, context, "While evaluating the filename to edit");
+            auto filename = state->coerceToString(noPos, v, context, "While evaluating the filename to edit: ");
             pos.file = state->symbols.create(*filename);
         } else if (v.isLambda()) {
             pos = v.lambda.fun->pos;
@@ -675,7 +675,7 @@ void NixRepl::reloadFiles()
 
 void NixRepl::addAttrsToScope(Value & attrs)
 {
-    state->forceAttrs(attrs, [&]() { return attrs.determinePos(noPos); }, "While evaluating an attribute set to be merged in the global scope");
+    state->forceAttrs(attrs, [&]() { return attrs.determinePos(noPos); }, "While evaluating an attribute set to be merged in the global scope: ");
     if (displ + attrs.attrs->size() >= envSize)
         throw Error("environment full; cannot add more variables");
 
@@ -780,7 +780,7 @@ 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, "While evaluating the drvPath of a derivation"));
+                str << state->store->printStorePath(state->coerceToStorePath(*i->pos, *i->value, context, "While evaluating the drvPath of a derivation: "));
             else
                 str << "???";
             str << "»";
diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index 1f433a199..ae314a7c6 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -144,7 +144,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         Bindings & bindings(*state->allocBindings(0));
         auto v2 = findAlongAttrPath(*state, settings.thisSystem, bindings, *v).first;
 
-        return store->parseStorePath(state->forceString(*v2, noPos, "While evaluating the path tho latest nix version"));
+        return store->parseStorePath(state->forceString(*v2, noPos, "While evaluating the path tho latest nix version: "));
     }
 };