fix Issue 11727 - Repeated error message with using forward reference…

…d enum as variable

src/expression.c

@@ -2030,10 +2030,11 @@ void Expression::deprecation(const char *format, ...)
     }
 }
 
-int Expression::rvalue()
+int Expression::rvalue(bool allowVoid)
 {
-    if (type && type->toBasetype()->ty == Tvoid)
-    {   error("expression %s is void and has no value", toChars());
+    if (!allowVoid && type && type->toBasetype()->ty == Tvoid)
+    {
+        error("expression %s is void and has no value", toChars());
 #if 0
         dump(0);
         halt();
@@ -4931,7 +4932,7 @@ Expression *TypeExp::semantic(Scope *sc)
     return e;
 }
 
-int TypeExp::rvalue()
+int TypeExp::rvalue(bool allowVoid)
 {
     error("type %s has no value", toChars());
     return 0;
@@ -5095,7 +5096,7 @@ void TemplateExp::toCBuffer(OutBuffer *buf, HdrGenState *hgs)
     buf->writestring(td->toChars());
 }
 
-int TemplateExp::rvalue()
+int TemplateExp::rvalue(bool allowVoid)
 {
     error("template %s has no value", toChars());
     return 0;

src/expression.h

@@ -136,7 +136,7 @@ class Expression : public RootObject
     void error(const char *format, ...);
     void warning(const char *format, ...);
     void deprecation(const char *format, ...);
-    virtual int rvalue();
+    virtual int rvalue(bool allowVoid = false);
 
     static Expression *combine(Expression *e1, Expression *e2);
     static Expressions *arraySyntaxCopy(Expressions *exps);
@@ -589,7 +589,7 @@ class TypeExp : public Expression
     TypeExp(Loc loc, Type *type);
     Expression *syntaxCopy();
     Expression *semantic(Scope *sc);
-    int rvalue();
+    int rvalue(bool allowVoid = false);
     void toCBuffer(OutBuffer *buf, HdrGenState *hgs);
     Expression *optimize(int result, bool keepLvalue = false);
     elem *toElem(IRState *irs);
@@ -614,7 +614,7 @@ class TemplateExp : public Expression
     FuncDeclaration *fd;
 
     TemplateExp(Loc loc, TemplateDeclaration *td, FuncDeclaration *fd = NULL);
-    int rvalue();
+    int rvalue(bool allowVoid = false);
     void toCBuffer(OutBuffer *buf, HdrGenState *hgs);
     int isLvalue();
     Expression *toLvalue(Scope *sc, Expression *e);

src/statement.c

@@ -3726,6 +3726,8 @@ Statement *ReturnStatement::semantic(Scope *sc)
             exp = exp->inferType(fld->treq->nextOf()->nextOf());
         exp = exp->semantic(sc);
         exp = resolveProperties(sc, exp);
+        if (!exp->rvalue(true)) // don't make error for void expression
+            exp = new ErrorExp();
         if (exp->op == TOKcall)
             exp = valueNoDtor(exp);
 

test/fail_compilation/diag11727.d

@@ -0,0 +1,39 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag11727.d(10): Error: type n has no value
+---
+*/
+auto returnEnum()
+{
+    enum n;
+    return n;
+}
+void main()
+{
+    assert(returnEnum() == 0);
+}
+
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag11727.d(26): Error: type void has no value
+---
+*/
+auto returnVoid()
+{
+    alias v = void;
+    return v;
+}
+
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag11727.d(38): Error: template t() has no value
+---
+*/
+auto returnTemplate()
+{
+    template t() {}
+    return t;
+}