Changes in src/AST/Expr.cpp [c36298d:ae265b55]

File:

• src/AST/Expr.cpp (modified) (6 diffs)

src/AST/Expr.cpp

@@ -20 +20 @@
 #include <vector>
 
+#include "Copy.hpp"                // for shallowCopy
+#include "Eval.hpp"                // for call
 #include "GenericSubstitution.hpp"
 #include "Stmt.hpp"
@@ -51 +53 @@
         assert( arg );
 
-        UntypedExpr * ret = new UntypedExpr{
-                loc, new NameExpr{loc, "*?"}, std::vector<ptr<Expr>>{ ptr<Expr>{ arg } }
-        };
+        UntypedExpr * ret = call( loc, "*?", arg );
         if ( const Type * ty = arg->result ) {
                 const Type * base = InitTweak::getPointerBase( ty );
@@ -74 +74 @@
         assert( lhs && rhs );
 
-        UntypedExpr * ret = new UntypedExpr{
-                loc, new NameExpr{loc, "?=?"}, std::vector<ptr<Expr>>{ ptr<Expr>{ lhs }, ptr<Expr>{ rhs } }
-        };
+        UntypedExpr * ret = call( loc, "?=?", lhs, rhs );
         if ( lhs->result && rhs->result ) {
                 // if both expressions are typed, assumes that this assignment is a C bitwise assignment,
@@ -160 +158 @@
         assert( aggregate->result );
 
-        // take ownership of member type
-        result = mem->get_type();
+        // Deep copy on result type avoids mutation on transitively multiply referenced object.
+        //
+        // Example, adapted from parts of builtins and bootloader:
+        //
+        // forall(dtype T)
+        // struct __Destructor {
+        //   T * object;
+        //   void (*dtor)(T *);
+        // };
+        //
+        // forall(dtype S)
+        // void foo(__Destructor(S) &d) {
+        //   if (d.dtor) {  // here
+        //   }
+        // }
+        //
+        // Let e be the "d.dtor" guard espression, which is MemberExpr after resolve.  Let d be the
+        // declaration of member __Destructor.dtor (an ObjectDecl), as accessed via the top-level
+        // declaration of __Destructor.  Consider the types e.result and d.type.  In the old AST, one
+        // is a clone of the other.  Ordinary new-AST use would set them up as a multiply-referenced
+        // object.
+        //
+        // e.result: PointerType
+        // .base: FunctionType
+        // .params.front(): ObjectDecl, the anonymous parameter of type T*
+        // .type: PointerType
+        // .base: TypeInstType
+        // let x = that
+        // let y = similar, except start from d.type
+        //
+        // Consider two code lines down, genericSubstitution(...).apply(result).
+        //
+        // Applying this chosen-candidate's type substitution means modifying x, substituting
+        // S for T.  This mutation should affect x and not y.
+
+        result = deepCopy(mem->get_type());
+
         // substitute aggregate generic parameters into member type
         genericSubstitution( aggregate->result ).apply( result );
@@ -168 +201 @@
 }
 
+MemberExpr::MemberExpr( const CodeLocation & loc, const DeclWithType * mem, const Expr * agg,
+    MemberExpr::NoOpConstruction overloadSelector )
+: Expr( loc ), member( mem ), aggregate( agg ) {
+        assert( member );
+        assert( aggregate );
+        assert( aggregate->result );
+        (void) overloadSelector;
+}
+
 // --- VariableExpr
 
@@ -177 +219 @@
         assert( var );
         assert( var->get_type() );
-        result = var->get_type();
-        add_qualifiers( result, CV::Lvalue );
+        auto r = shallowCopy( var->get_type() );
+        r->qualifiers |= CV::Lvalue;
+        result = r;
 }