Issue 9017 - __traits(compiles, { enum e = <expression tuple>; }) is true but code doesn't compile

src/cast.c

@@ -1566,6 +1566,9 @@ Expression *AddrExp::castTo(Scope *sc, Type *t)
 
 Expression *TupleExp::castTo(Scope *sc, Type *t)
 {
+    if (type->equals(t))
+        return this;
+
     TupleExp *e = (TupleExp *)copy();
     e->e0 = e0 ? e0->copy() : NULL;
     e->exps = (Expressions *)exps->copy();

src/declaration.c

@@ -1126,6 +1126,7 @@ void VarDeclaration::semantic(Scope *sc)
             }
 
             VarDeclaration *v = new VarDeclaration(loc, arg->type, id, ti);
+            v->storage_class |= storage_class;
             if (arg->storageClass & STCparameter)
                 v->storage_class |= arg->storageClass;
             //printf("declaring field %s of type %s\n", v->toChars(), v->type->toChars());

src/template.c

@@ -6439,6 +6439,18 @@ int TemplateInstance::hasNestedArgs(Objects *args)
                     sa = ((FuncExp *)ea)->fd;
                 goto Lsa;
             }
+            // Emulate Expression::toMangleBuffer call that had exist in TemplateInstance::genIdent.
+            if (ea->op != TOKint64 &&               // IntegerExp
+                ea->op != TOKfloat64 &&             // RealExp
+                ea->op != TOKcomplex80 &&           // CompexExp
+                ea->op != TOKnull &&                // NullExp
+                ea->op != TOKstring &&              // StringExp
+                ea->op != TOKarrayliteral &&        // ArrayLiteralExp
+                ea->op != TOKassocarrayliteral &&   // AssocArrayLiteralExp
+                ea->op != TOKstructliteral)         // StructLiteralExp
+            {
+                ea->error("expression %s is not a valid template value argument", ea->toChars());
+            }
         }
         else if (sa)
         {

test/fail_compilation/fail235.d

@@ -1,11 +1,24 @@
 /*
-Error: expression & D10TypeInfo_a6__initZ is not a valid template value argument
-
-a.d(7): template instance a.Tuple!(& D10TypeInfo_a6__initZ) error instantiating
+test_output:
+---
+fail_compilation/fail235.d(12): Error: expression & _D10TypeInfo_a6__initZ is not a valid template value argument
+---
 */
 template Tuple(TPL...)
 {
     alias TPL Tuple;
 }
 
 auto K = Tuple!(typeid(char));
+
+/*
+test_output:
+---
+fail_compilation/fail235.d(24): Error: expression & _D10TypeInfo_a6__initZ is not a valid template value argument
+---
+*/
+template Alias(alias A)
+{
+    alias A Alias;
+}
+auto A = Alias!(typeid(char));