Fix for PR18393 - emit error when abstract type is returned by value

[matekm]

Summary

Clang doesn't emit error message when return type of declared method is an abstract type. This error is catched when method is defined but it would be cool to catch it as soon as possible.

This patch removes check that prevented checking if method return type is abstract in record context. I also added additional test to prevent regression in this context.

Br,
Robert

[matekm]

Update diff as tests were not complete - check for note was missing

[rsmith]

We need to defer this check in the case where the type in question is still being defined.

lib/Sema/SemaDecl.cpp

6497–6498

This comment describes how this case is intended to be handled; we need more digging to figure out what's actually wrong here.

lib/Sema/SemaDecl.cpp

   // Check that the return type is not an abstract class type.
   // For record types, this is done by the AbstractClassUsageDiagnoser once
   // the class has been completely parsed.
-  if (!DC->isRecord() &&
-      SemaRef.RequireNonAbstractType(
+  if (SemaRef.RequireNonAbstractType(
           D.getIdentifierLoc(), R->getAs<FunctionType>()->getReturnType(),
           diag::err_abstract_type_in_decl, SemaRef.AbstractReturnType))
     D.setInvalidType();

test/SemaCXX/abstract.cpp

     RedundantInit() : A(0) {} // expected-warning {{initializer for virtual base class 'pr16659::A' of abstract class 'RedundantInit' will never be used}}
   };
 }
+
+namespace PR18393 {
+  struct A {
+      virtual void f() = 0; // expected-note {{unimplemented pure virtual method 'f' in 'A'}}
+  };
+
+  struct B {
+      A f(); // expected-error {{return type 'PR18393::A' is an abstract class}}
+  };
+}
+