don't repeatedly look up ast internal symbols

these symbols are used a *lot*, so it makes sense to cache them. this
mostly increases clarity of the code (however clear one may wish to call
the parser desugaring here), but it also provides a small performance
benefit.

src/libexpr/eval.cc

@@ -419,6 +419,16 @@ EvalState::EvalState(
     , sPath(symbols.create("path"))
     , sPrefix(symbols.create("prefix"))
     , sOutputSpecified(symbols.create("outputSpecified"))
+    , exprSymbols{
+        .sub = symbols.create("__sub"),
+        .lessThan = symbols.create("__lessThan"),
+        .mul = symbols.create("__mul"),
+        .div = symbols.create("__div"),
+        .or_ = symbols.create("or"),
+        .findFile = symbols.create("__findFile"),
+        .nixPath = symbols.create("__nixPath"),
+        .body = symbols.create("body")
+    }
     , repair(NoRepair)
     , emptyBindings(0)
     , rootFS(
@@ -2808,7 +2818,7 @@ Expr * EvalState::parse(
     const SourcePath & basePath,
     std::shared_ptr<StaticEnv> & staticEnv)
 {
-    auto result = parseExprFromBuf(text, length, origin, basePath, symbols, positions, rootFS);
+    auto result = parseExprFromBuf(text, length, origin, basePath, symbols, positions, rootFS, exprSymbols);
 
     result->bindVars(*this, staticEnv);
 

src/libexpr/eval.hh

@@ -207,6 +207,8 @@ public:
         sPrefix,
         sOutputSpecified;
 
+    const Expr::AstSymbols exprSymbols;
+
     /**
      * If set, force copying files to the Nix store even if they
      * already exist there.

src/libexpr/nixexpr.hh

@@ -140,6 +140,11 @@ std::string showAttrPath(const SymbolTable & symbols, const AttrPath & attrPath)
 
 struct Expr
 {
+    struct AstSymbols {
+        Symbol sub, lessThan, mul, div, or_, findFile, nixPath, body;
+    };
+
+
     static unsigned long nrExprs;
     Expr() {
         nrExprs++;

src/libexpr/parser-state.hh

@@ -43,6 +43,7 @@ struct ParserState {
     SourcePath basePath;
     PosTable::Origin origin;
     const ref<InputAccessor> rootFS;
+    const Expr::AstSymbols & s;
 
     void dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos);
     void dupAttr(Symbol attr, const PosIdx pos, const PosIdx prevPos);

src/libexpr/parser.y

@@ -41,7 +41,8 @@ Expr * parseExprFromBuf(
     const SourcePath & basePath,
     SymbolTable & symbols,
     PosTable & positions,
-    const ref<InputAccessor> rootFS);
+    const ref<InputAccessor> rootFS,
+    const Expr::AstSymbols & astSymbols);
 
 }
 
@@ -168,13 +169,13 @@ expr_if
 
 expr_op
   : '!' expr_op %prec NOT { $$ = new ExprOpNot($2); }
-  | '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(state->symbols.create("__sub")), {new ExprInt(0), $2}); }
+  | '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(state->s.sub), {new ExprInt(0), $2}); }
   | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
   | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
-  | expr_op '<' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->symbols.create("__lessThan")), {$1, $3}); }
+  | expr_op '<' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->s.lessThan), {$1, $3}); }
-  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprCall(state->at(@2), new ExprVar(state->symbols.create("__lessThan")), {$3, $1})); }
+  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprCall(state->at(@2), new ExprVar(state->s.lessThan), {$3, $1})); }
-  | expr_op '>' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->symbols.create("__lessThan")), {$3, $1}); }
+  | expr_op '>' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->s.lessThan), {$3, $1}); }
-  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprCall(state->at(@2), new ExprVar(state->symbols.create("__lessThan")), {$1, $3})); }
+  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprCall(state->at(@2), new ExprVar(state->s.lessThan), {$1, $3})); }
   | expr_op AND expr_op { $$ = new ExprOpAnd(state->at(@2), $1, $3); }
   | expr_op OR expr_op { $$ = new ExprOpOr(state->at(@2), $1, $3); }
   | expr_op IMPL expr_op { $$ = new ExprOpImpl(state->at(@2), $1, $3); }
@@ -182,9 +183,9 @@ expr_op
   | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, std::move(*$3)); delete $3; }
   | expr_op '+' expr_op
     { $$ = new ExprConcatStrings(state->at(@2), false, new std::vector<std::pair<PosIdx, Expr *> >({{state->at(@1), $1}, {state->at(@3), $3}})); }
-  | expr_op '-' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->symbols.create("__sub")), {$1, $3}); }
+  | expr_op '-' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->s.sub), {$1, $3}); }
-  | expr_op '*' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->symbols.create("__mul")), {$1, $3}); }
+  | expr_op '*' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->s.mul), {$1, $3}); }
-  | expr_op '/' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->symbols.create("__div")), {$1, $3}); }
+  | expr_op '/' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->s.div), {$1, $3}); }
   | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists(state->at(@2), $1, $3); }
   | expr_app
   ;
@@ -208,7 +209,7 @@ expr_select
   | /* Backwards compatibility: because Nixpkgs has a rarely used
        function named ‘or’, allow stuff like ‘map or [...]’. */
     expr_simple OR_KW
-    { $$ = new ExprCall(CUR_POS, $1, {new ExprVar(CUR_POS, state->symbols.create("or"))}); }
+    { $$ = new ExprCall(CUR_POS, $1, {new ExprVar(CUR_POS, state->s.or_)}); }
   | expr_simple
   ;
 
@@ -235,8 +236,8 @@ expr_simple
   | SPATH {
       std::string path($1.p + 1, $1.l - 2);
       $$ = new ExprCall(CUR_POS,
-          new ExprVar(state->symbols.create("__findFile")),
+          new ExprVar(state->s.findFile),
-          {new ExprVar(state->symbols.create("__nixPath")),
+          {new ExprVar(state->s.nixPath),
            new ExprString(std::move(path))});
   }
   | URI {
@@ -252,7 +253,7 @@ expr_simple
   /* Let expressions `let {..., body = ...}' are just desugared
      into `(rec {..., body = ...}).body'. */
   | LET '{' binds '}'
-    { $3->recursive = true; $$ = new ExprSelect(noPos, $3, state->symbols.create("body")); }
+    { $3->recursive = true; $$ = new ExprSelect(noPos, $3, state->s.body); }
   | REC '{' binds '}'
     { $3->recursive = true; $$ = $3; }
   | '{' binds '}'
@@ -414,7 +415,8 @@ Expr * parseExprFromBuf(
     const SourcePath & basePath,
     SymbolTable & symbols,
     PosTable & positions,
-    const ref<InputAccessor> rootFS)
+    const ref<InputAccessor> rootFS,
+    const Expr::AstSymbols & astSymbols)
 {
     yyscan_t scanner;
     ParserState state {
@@ -423,6 +425,7 @@ Expr * parseExprFromBuf(
         .basePath = basePath,
         .origin = {origin},
         .rootFS = rootFS,
+        .s = astSymbols,
     };
 
     yylex_init(&scanner);