parser.y: abstract new into a function on Exprs

so it can easily be swapped out for other implementations

Author: Radvendii

src/libexpr/eval.cc

@@ -3216,8 +3216,8 @@ Expr * EvalState::parse(
         docComments = &it->second;
     }
 
-    auto result = parseExprFromBuf(
-        text, length, origin, basePath, mem.exprs, symbols, settings, positions, *docComments, rootFS);
+    auto result =
+        parseExprFromBuf(text, length, origin, basePath, mem.exprs, symbols, settings, positions, *docComments, rootFS);
 
     result->bindVars(*this, staticEnv);
 

src/libexpr/include/nix/expr/nixexpr.hh

@@ -91,13 +91,6 @@ std::string showAttrPath(const SymbolTable & symbols, std::span<const AttrName>
 
 using UpdateQueue = SmallTemporaryValueVector<conservativeStackReservation>;
 
-class Exprs
-{
-    std::pmr::monotonic_buffer_resource buffer;
-public:
-    std::pmr::polymorphic_allocator<char> alloc{&buffer};
-};
-
 /* Abstract syntax of Nix expressions. */
 
 struct Expr
@@ -810,6 +803,49 @@ struct ExprBlackHole : Expr
 
 extern ExprBlackHole eBlackHole;
 
+class Exprs
+{
+    std::pmr::monotonic_buffer_resource buffer;
+public:
+    std::pmr::polymorphic_allocator<char> alloc{&buffer};
+
+    template<class C>
+    [[gnu::always_inline]]
+    C * add(auto &&... args)
+    {
+        return new C(std::forward<decltype(args)>(args)...);
+    }
+
+    // we define some calls to add explicitly so that the argument can be passed in as initializer lists
+    template<class C>
+    [[gnu::always_inline]]
+    C * add(const PosIdx & pos, Expr * fun, std::vector<Expr *> && args)
+        requires(std::same_as<C, ExprCall>)
+    {
+        return new C(pos, fun, std::move(args));
+    }
+
+    template<class C>
+    [[gnu::always_inline]]
+    C * add(const PosIdx & pos, Expr * fun, std::vector<Expr *> && args, PosIdx && cursedOrEndPos)
+        requires(std::same_as<C, ExprCall>)
+    {
+        return new C(pos, fun, std::move(args), std::move(cursedOrEndPos));
+    }
+
+    template<class C>
+    [[gnu::always_inline]]
+    C *
+    add(std::pmr::polymorphic_allocator<char> & alloc,
+        const PosIdx & pos,
+        bool forceString,
+        const std::vector<std::pair<PosIdx, Expr *>> & es)
+        requires(std::same_as<C, ExprConcatStrings>)
+    {
+        return alloc.new_object<C>(alloc, pos, forceString, es);
+    }
+};
+
 /* Static environments are used to map variable names onto (level,
    displacement) pairs used to obtain the value of the variable at
    runtime. */

src/libexpr/include/nix/expr/parser-state.hh

@@ -132,11 +132,11 @@ inline void ParserState::addAttr(
                     dupAttr(attrPath, pos, j->second.pos);
                 }
             } else {
-                nested = new ExprAttrs;
+                nested = exprs.add<ExprAttrs>();
                 attrs->attrs[i->symbol] = ExprAttrs::AttrDef(nested, pos);
             }
         } else {
-            nested = new ExprAttrs;
+            nested = exprs.add<ExprAttrs>();
             attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, nested, pos));
         }
         attrs = nested;
@@ -240,7 +240,7 @@ inline Expr *
 ParserState::stripIndentation(const PosIdx pos, std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>> && es)
 {
     if (es.empty())
-        return new ExprString("");
+        return exprs.add<ExprString>("");
 
     /* Figure out the minimum indentation.  Note that by design
        whitespace-only final lines are not taken into account.  (So
@@ -322,7 +322,7 @@ ParserState::stripIndentation(const PosIdx pos, std::vector<std::pair<PosIdx, st
 
         // Ignore empty strings for a minor optimisation and AST simplification
         if (s2 != "") {
-            es2.emplace_back(i->first, new ExprString(exprs.alloc, s2));
+            es2.emplace_back(i->first, exprs.add<ExprString>(exprs.alloc, s2));
         }
     };
     for (; i != es.end(); ++i, --n) {
@@ -332,7 +332,7 @@ ParserState::stripIndentation(const PosIdx pos, std::vector<std::pair<PosIdx, st
     // If there is nothing at all, return the empty string directly.
     // This also ensures that equivalent empty strings result in the same ast, which is helpful when testing formatters.
     if (es2.size() == 0) {
-        auto * const result = new ExprString("");
+        auto * const result = exprs.add<ExprString>("");
         return result;
     }
 
@@ -341,7 +341,7 @@ ParserState::stripIndentation(const PosIdx pos, std::vector<std::pair<PosIdx, st
         auto * const result = (es2)[0].second;
         return result;
     }
-    return new ExprConcatStrings(exprs.alloc, pos, true, std::move(es2));
+    return exprs.add<ExprConcatStrings>(exprs.alloc, pos, true, std::move(es2));
 }
 
 inline PosIdx LexerState::at(const ParserLocation & loc)