Don't use any syntactic sugar for dynamic attrs

This doesn't change any functionality but moves some behavior out of the
parser and into the evaluator in order to simplify the code.

Signed-off-by: Shea Levy <shea@shealevy.com>

src/libexpr/eval.cc

@@ -129,6 +129,18 @@ string showType(const Value & v)
 }
 
 
+Symbol getName(const AttrName & name, EvalState & state, Env & env) {
+    if (name.symbol.set()) {
+        return name.symbol;
+    } else {
+        Value nameValue;
+        name.expr->eval(state, env, nameValue);
+        state.forceStringNoCtx(nameValue);
+        return state.symbols.create(nameValue.string.s);
+    }
+}
+
+
 EvalState::EvalState()
     : sWith(symbols.create("<with>"))
     , sOutPath(symbols.create("outPath"))
@@ -683,17 +695,18 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
         foreach (AttrPath::const_iterator, i, attrPath) {
             nrLookups++;
             Bindings::iterator j;
+            Symbol name = getName(*i, state, env);
             if (def) {
                 state.forceValue(*vAttrs);
                 if (vAttrs->type != tAttrs ||
-                    (j = vAttrs->attrs->find(*i)) == vAttrs->attrs->end())
+                    (j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
                 {
                     def->eval(state, env, v);
                     return;
                 }
             } else {
                 state.forceAttrs(*vAttrs);
-                if ((j = vAttrs->attrs->find(*i)) == vAttrs->attrs->end())
+                if ((j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
                     throwEvalError("attribute `%1%' missing", showAttrPath(attrPath));
             }
             vAttrs = j->value;
@@ -724,8 +737,9 @@ void ExprOpHasAttr::eval(EvalState & state, Env & env, Value & v)
     foreach (AttrPath::const_iterator, i, attrPath) {
         state.forceValue(*vAttrs);
         Bindings::iterator j;
+        Symbol name = getName(*i, state, env);
         if (vAttrs->type != tAttrs ||
-            (j = vAttrs->attrs->find(*i)) == vAttrs->attrs->end())
+            (j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
         {
             mkBool(v, false);
             return;

src/libexpr/nixexpr.cc

@@ -155,12 +155,19 @@ std::ostream & operator << (std::ostream & str, const Pos & pos)
 
 string showAttrPath(const AttrPath & attrPath)
 {
-    string s;
+    std::ostringstream out;
+    bool first = true;
     foreach (AttrPath::const_iterator, i, attrPath) {
-        if (!s.empty()) s += '.';
-        s += *i;
+        if (!first)
+            out << '.';
+        else
+            first = false;
+        if (i->symbol.set())
+            out << i->symbol;
+        else
+            out << "\"${" << *i->expr << "}\"";
     }
-    return s;
+    return out.str();
 }
 
 
@@ -220,11 +227,17 @@ void ExprSelect::bindVars(const StaticEnv & env)
 {
     e->bindVars(env);
     if (def) def->bindVars(env);
+    foreach (AttrPath::iterator, i, attrPath)
+        if (!i->symbol.set())
+            i->expr->bindVars(env);
 }
 
 void ExprOpHasAttr::bindVars(const StaticEnv & env)
 {
     e->bindVars(env);
+    foreach (AttrPath::iterator, i, attrPath)
+        if (!i->symbol.set())
+            i->expr->bindVars(env);
 }
 
 void ExprAttrs::bindVars(const StaticEnv & env)

src/libexpr/nixexpr.hh

@@ -50,10 +50,19 @@ struct Env;
 struct Value;
 struct EvalState;
 struct StaticEnv;
+struct Expr;
 
 
 /* An attribute path is a sequence of attribute names. */
-typedef vector<Symbol> AttrPath;
+struct AttrName
+{
+    Symbol symbol;
+    Expr *expr;
+    AttrName(const Symbol & s) : symbol(s) {};
+    AttrName(Expr *e) : expr(e) {};
+};
+
+typedef std::vector<AttrName> AttrPath;
 
 string showAttrPath(const AttrPath & attrPath);
 
@@ -138,7 +147,7 @@ struct ExprSelect : Expr
     Expr * e, * def;
     AttrPath attrPath;
     ExprSelect(Expr * e, const AttrPath & attrPath, Expr * def) : e(e), def(def), attrPath(attrPath) { };
-    ExprSelect(Expr * e, const Symbol & name) : e(e), def(0) { attrPath.push_back(name); };
+    ExprSelect(Expr * e, const Symbol & name) : e(e), def(0) { attrPath.push_back(AttrName(name)); };
     COMMON_METHODS
 };
 

src/libexpr/parser.y

@@ -39,15 +39,6 @@ namespace nix {
             { };
     };
 
-    struct AttrName
-    {
-        Symbol symbol;
-        Expr *expr;
-        AttrName(const Symbol & s) : symbol(s) {};
-        AttrName(Expr *e) : expr(e) {};
-    };
-
-    typedef std::vector<AttrName> AttrNames;
 }
 
 #define YY_DECL int yylex \
@@ -83,32 +74,28 @@ static void dupAttr(const AttrPath & attrPath, const Pos & pos, const Pos & prev
 
 static void dupAttr(Symbol attr, const Pos & pos, const Pos & prevPos)
 {
-    AttrPath attrPath; attrPath.push_back(attr);
     throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
-        % showAttrPath(attrPath) % pos % prevPos);
+        % attr % pos % prevPos);
 }
 
 
-static void addAttr(ExprAttrs * attrs, AttrNames & attrNames,
+static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
     Expr * e, const Pos & pos)
 {
-    AttrPath path;
-    AttrNames::iterator i;
+    AttrPath::iterator i;
     // All attrpaths have at least one attr
-    assert(!attrNames.empty());
-    for (i = attrNames.begin(); i + 1 < attrNames.end(); i++) {
+    assert(!attrPath.empty());
+    for (i = attrPath.begin(); i + 1 < attrPath.end(); i++) {
         if (i->symbol.set()) {
-            path.push_back(i->symbol);
             ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
             if (j != attrs->attrs.end()) {
                 if (!j->second.inherited) {
                     ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.e);
-                    if (!attrs2) dupAttr(path, pos, j->second.pos);
+                    if (!attrs2) dupAttr(attrPath, pos, j->second.pos);
                     attrs = attrs2;
                 } else
-                    dupAttr(path, pos, j->second.pos);
+                    dupAttr(attrPath, pos, j->second.pos);
             } else {
-                path.clear();
                 ExprAttrs * nested = new ExprAttrs;
                 attrs->attrs[i->symbol] = ExprAttrs::AttrDef(nested, pos);
                 attrs = nested;
@@ -122,7 +109,7 @@ static void addAttr(ExprAttrs * attrs, AttrNames & attrNames,
     if (i->symbol.set()) {
         ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
         if (j != attrs->attrs.end()) {
-            dupAttr(path, pos, j->second.pos);
+            dupAttr(attrPath, pos, j->second.pos);
         } else {
             attrs->attrs[i->symbol] = ExprAttrs::AttrDef(e, pos);
             e->setName(i->symbol);
@@ -268,8 +255,7 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
   char * id; // !!! -> Symbol
   char * path;
   char * uri;
-  std::vector<nix::AttrName> * attrpath;
-  std::vector<nix::Symbol> * attrlist;
+  std::vector<nix::AttrName> * attrNames;
   std::vector<nix::Expr *> * string_parts;
 }
 
@@ -279,8 +265,7 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
 %type <attrs> binds
 %type <formals> formals
 %type <formal> formal
-%type <attrpath> attrpath
-%type <attrlist> attrs
+%type <attrNames> attrs attrpath
 %type <string_parts> string_parts_interpolated ind_string_parts
 %type <e> string_parts string_attr
 %type <id> attr
@@ -354,39 +339,7 @@ expr_op
   | expr_op OR expr_op { $$ = new ExprOpOr($1, $3); }
   | expr_op IMPL expr_op { $$ = new ExprOpImpl($1, $3); }
   | expr_op UPDATE expr_op { $$ = new ExprOpUpdate($1, $3); }
-  | expr_op '?' attrpath
-    { AttrPath path;
-      vector<AttrName>::iterator i;
-      $$ = $1;
-      // All attrpaths have at least one attr
-      assert(!$3->empty());
-      for (i = $3->begin(); i + 1 != $3->end(); i++) {
-          if (i->symbol.set()) {
-              path.push_back(i->symbol);
-          } else {
-              if (!path.empty()) {
-                  $$ = new ExprSelect($$, path, new ExprAttrs());
-                  path.clear();
-              }
-              $$ = new ExprIf(
-                new ExprOpAnd(
-                  new ExprApp(new ExprBuiltin(data->symbols.create("isAttrs")), $$),
-                  new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("hasAttr")), i->expr), $$)),
-                new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("getAttr")), i->expr), $$),
-                new ExprAttrs());
-          }
-      }
-      if (i->symbol.set()) {
-          path.push_back(i->symbol);
-          $$ = new ExprOpHasAttr($$, path);
-      } else {
-          if (!path.empty())
-              $$ = new ExprSelect($$, path, new ExprAttrs());
-          $$ = new ExprOpAnd(
-            new ExprApp(new ExprBuiltin(data->symbols.create("isAttrs")), $$),
-            new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("hasAttr")), i->expr), $$));
-      }
-    }
+  | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, *$3); }
   | expr_op '+' expr_op
     { vector<Expr *> * l = new vector<Expr *>;
       l->push_back($1);
@@ -408,58 +361,9 @@ expr_app
 
 expr_select
   : expr_simple '.' attrpath
-    { AttrPath path;
-      $$ = $1;
-      foreach (vector<AttrName>::iterator, i, *$3) {
-          if (i->symbol.set()) {
-              path.push_back(i->symbol);
-          } else {
-              if (!path.empty()) {
-                  $$ = new ExprSelect($$, path, 0);
-                  path.clear();
-              }
-              $$ = new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("getAttr")), i->expr), $$);
-          }
-      }
-      if (!path.empty())
-          $$ = new ExprSelect($$, path, 0);
-    }
+    { $$ = new ExprSelect($1, *$3, 0); }
   | expr_simple '.' attrpath OR_KW expr_select
-    { AttrPath path;
-      vector<AttrName>::iterator i;
-      $$ = $1;
-      // All attrpaths have at least one attr
-      assert(!$3->empty());
-      for (i = $3->begin(); i + 1 != $3->end(); i++) {
-          if (i->symbol.set()) {
-              path.push_back(i->symbol);
-          } else {
-              if (!path.empty()) {
-                  $$ = new ExprSelect($$, path, new ExprAttrs());
-                  path.clear();
-              }
-              $$ = new ExprIf(
-                new ExprOpAnd(
-                  new ExprApp(new ExprBuiltin(data->symbols.create("isAttrs")), $$),
-                  new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("hasAttr")), i->expr), $$)),
-                new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("getAttr")), i->expr), $$),
-                new ExprAttrs());
-          }
-      }
-      if (i->symbol.set()) {
-          path.push_back(i->symbol);
-          $$ = new ExprSelect($$, path, $5);
-      } else {
-          if (!path.empty())
-              $$ = new ExprSelect($$, path, new ExprAttrs());
-          $$ = new ExprIf(
-            new ExprOpAnd(
-                new ExprApp(new ExprBuiltin(data->symbols.create("isAttrs")), $$),
-                new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("hasAttr")), i->expr), $$)),
-            new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("getAttr")), i->expr), $$),
-            $5);
-      }
-    }
+    { $$ = new ExprSelect($1, *$3, $5); }
   | /* Backwards compatibility: because Nixpkgs has a rarely used
        function named ‘or’, allow stuff like ‘map or [...]’. */
     expr_simple OR_KW
@@ -542,37 +446,37 @@ binds
   | binds INHERIT attrs ';'
     { $$ = $1;
       foreach (AttrPath::iterator, i, *$3) {
-          if ($$->attrs.find(*i) != $$->attrs.end())
-              dupAttr(*i, makeCurPos(@3, data), $$->attrs[*i].pos);
+          if ($$->attrs.find(i->symbol) != $$->attrs.end())
+              dupAttr(i->symbol, makeCurPos(@3, data), $$->attrs[i->symbol].pos);
           Pos pos = makeCurPos(@3, data);
-          $$->attrs[*i] = ExprAttrs::AttrDef(new ExprVar(CUR_POS, *i), pos, true);
+          $$->attrs[i->symbol] = ExprAttrs::AttrDef(new ExprVar(CUR_POS, i->symbol), pos, true);
       }
     }
   | binds INHERIT '(' expr ')' attrs ';'
     { $$ = $1;
       /* !!! Should ensure sharing of the expression in $4. */
-      foreach (vector<Symbol>::iterator, i, *$6) {
-          if ($$->attrs.find(*i) != $$->attrs.end())
-              dupAttr(*i, makeCurPos(@6, data), $$->attrs[*i].pos);
-          $$->attrs[*i] = ExprAttrs::AttrDef(new ExprSelect($4, *i), makeCurPos(@6, data));
+      foreach (AttrPath::iterator, i, *$6) {
+          if ($$->attrs.find(i->symbol) != $$->attrs.end())
+              dupAttr(i->symbol, makeCurPos(@6, data), $$->attrs[i->symbol].pos);
+          $$->attrs[i->symbol] = ExprAttrs::AttrDef(new ExprSelect($4, i->symbol), makeCurPos(@6, data));
       }
     }
   | { $$ = new ExprAttrs; }
   ;
 
 attrs
-  : attrs attr { $$ = $1; $1->push_back(data->symbols.create($2)); /* !!! dangerous */ }
+  : attrs attr { $$ = $1; $1->push_back(AttrName(data->symbols.create($2))); }
   | attrs string_attr
     { $$ = $1;
       ExprString *str = dynamic_cast<ExprString *>($2);
       if (str) {
-          $$->push_back(str->s);
+          $$->push_back(AttrName(str->s));
           delete str;
       } else
         throw ParseError(format("dynamic attributes not allowed in inherit at %1%")
             % makeCurPos(@2, data));
     }
-  | { $$ = new vector<Symbol>; }
+  | { $$ = new AttrPath; }
   ;
 
 attrpath