report inherit attr errors at the duplicate name

previously we reported the error at the beginning of the binding
block (for plain inherits) or the beginning of the attr list (for
inherit-from), effectively hiding where exactly the error happened.

this also carries over to runtime positions of attributes in sets as
reported by unsafeGetAttrPos. we're not worried about this changing
observable eval behavior because it *is* marked unsafe, and the new
behavior is much more useful.

doc/manual/rl-next/inherit-error-positions.md

@@ -0,0 +1,6 @@
+---
+synopsis: fix duplicate attribute error positions for `inherit`
+prs: 9874
+---
+
+When an inherit caused a duplicate attribute error the position of the error was not reported correctly, placing the error with the inherit itself or at the start of the bindings block instead of the offending attribute name.

src/libexpr/parser.y

@@ -87,6 +87,7 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParserState * state, const char *
   nix::StringToken uri;
   nix::StringToken str;
   std::vector<nix::AttrName> * attrNames;
+  std::vector<std::pair<nix::AttrName, nix::PosIdx>> * inheritAttrs;
   std::vector<std::pair<nix::PosIdx, nix::Expr *>> * string_parts;
   std::vector<std::pair<nix::PosIdx, std::variant<nix::Expr *, nix::StringToken>>> * ind_string_parts;
 }
@@ -97,7 +98,8 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParserState * state, const char *
 %type <attrs> binds
 %type <formals> formals
 %type <formal> formal
-%type <attrNames> attrs attrpath
+%type <attrNames> attrpath
+%type <inheritAttrs> attrs
 %type <string_parts> string_parts_interpolated
 %type <ind_string_parts> ind_string_parts
 %type <e> path_start string_parts string_attr
@@ -309,13 +311,12 @@ binds
   : binds attrpath '=' expr ';' { $$ = $1; state->addAttr($$, std::move(*$2), $4, state->at(@2)); delete $2; }
   | binds INHERIT attrs ';'
     { $$ = $1;
-      for (auto & i : *$3) {
+      for (auto & [i, iPos] : *$3) {
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
-              state->dupAttr(i.symbol, state->at(@3), $$->attrs[i.symbol].pos);
+              state->dupAttr(i.symbol, iPos, $$->attrs[i.symbol].pos);
-          auto pos = state->at(@3);
           $$->attrs.emplace(
               i.symbol,
-              ExprAttrs::AttrDef(new ExprVar(CUR_POS, i.symbol), pos, ExprAttrs::AttrDef::Kind::Inherited));
+              ExprAttrs::AttrDef(new ExprVar(iPos, i.symbol), iPos, ExprAttrs::AttrDef::Kind::Inherited));
       }
       delete $3;
     }
@@ -325,14 +326,14 @@ binds
           $$->inheritFromExprs = std::make_unique<std::vector<Expr *>>();
       $$->inheritFromExprs->push_back($4);
       auto from = new nix::ExprInheritFrom(state->at(@4), $$->inheritFromExprs->size() - 1);
-      for (auto & i : *$6) {
+      for (auto & [i, iPos] : *$6) {
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
-              state->dupAttr(i.symbol, state->at(@6), $$->attrs[i.symbol].pos);
+              state->dupAttr(i.symbol, iPos, $$->attrs[i.symbol].pos);
           $$->attrs.emplace(
               i.symbol,
               ExprAttrs::AttrDef(
-                  new ExprSelect(CUR_POS, from, i.symbol),
+                  new ExprSelect(iPos, from, i.symbol),
-                  state->at(@6),
+                  iPos,
                   ExprAttrs::AttrDef::Kind::InheritedFrom));
       }
       delete $6;
@@ -341,12 +342,12 @@ binds
   ;
 
 attrs
-  : attrs attr { $$ = $1; $1->push_back(AttrName(state->symbols.create($2))); }
+  : attrs attr { $$ = $1; $1->emplace_back(AttrName(state->symbols.create($2)), state->at(@2)); }
   | attrs string_attr
     { $$ = $1;
       ExprString * str = dynamic_cast<ExprString *>($2);
       if (str) {
-          $$->push_back(AttrName(state->symbols.create(str->s)));
+          $$->emplace_back(AttrName(state->symbols.create(str->s)), state->at(@2));
           delete str;
       } else
           throw ParseError({
@@ -354,7 +355,7 @@ attrs
               .pos = state->positions[state->at(@2)]
           });
     }
-  | { $$ = new AttrPath; }
+  | { $$ = new std::vector<std::pair<AttrName, PosIdx>>; }
   ;
 
 attrpath

tests/functional/lang/eval-okay-inherit-attr-pos.exp

@@ -0,0 +1 @@
+[ { column = 17; file = "/pwd/lang/eval-okay-inherit-attr-pos.nix"; line = 4; } { column = 19; file = "/pwd/lang/eval-okay-inherit-attr-pos.nix"; line = 4; } { column = 21; file = "/pwd/lang/eval-okay-inherit-attr-pos.nix"; line = 5; } { column = 23; file = "/pwd/lang/eval-okay-inherit-attr-pos.nix"; line = 5; } ]

tests/functional/lang/eval-okay-inherit-attr-pos.nix

@@ -0,0 +1,12 @@
+let
+  d = 0;
+  x = 1;
+  y = { inherit d x; };
+  z = { inherit (y) d x; };
+in
+  [
+    (builtins.unsafeGetAttrPos "d" y)
+    (builtins.unsafeGetAttrPos "x" y)
+    (builtins.unsafeGetAttrPos "d" z)
+    (builtins.unsafeGetAttrPos "x" z)
+  ]

tests/functional/lang/parse-fail-dup-attrs-2.err.exp

@@ -1,5 +1,5 @@
 error: attribute 'x' already defined at «stdin»:9:5
-       at «stdin»:10:17:
+       at «stdin»:10:18:
             9|     x = 789;
            10|     inherit (as) x;
              |                  ^

tests/functional/lang/parse-fail-dup-attrs-3.err.exp

@@ -1,5 +1,5 @@
 error: attribute 'x' already defined at «stdin»:9:5
-       at «stdin»:10:17:
+       at «stdin»:10:18:
             9|     x = 789;
            10|     inherit (as) x;
              |                  ^

tests/functional/lang/parse-fail-dup-attrs-7.err.exp

@@ -1,5 +1,5 @@
-error: attribute 'x' already defined at «stdin»:6:12
+error: attribute 'x' already defined at «stdin»:6:13
-       at «stdin»:7:12:
+       at «stdin»:7:13:
             6|     inherit x;
             7|     inherit x;
              |             ^

tests/functional/lang/parse-fail-regression-20060610.err.exp

@@ -1,6 +1,6 @@
 error: undefined variable 'gcc'
-       at «stdin»:8:12:
+       at «stdin»:9:13:
-            7|
             8|   body = ({
-             |            ^
             9|     inherit gcc;
+             |             ^
+           10|   }).gcc;