[PATCH] Fix for PR18393 - emit error when abstract type is returned or taken by value

[Robert Matusewicz]

>>! In D5409#4, @rsmith wrote:
> Clang doesn't do this immediately because that's not correct:
> 
>   struct S {
>     S f();
>     virtual void g() = 0;
>   };
> 
> We can't tell that we need to diagnose `f` until we reach the declaration
> of `g`.

Hi,

actually after applying my patch the case you presented is handled correctly. The problematic case is this one:

   struct AbstractClass;

   struct S {
     AbstractClass f();
   };

   struct AbstracClass {
      virtual void g() = 0;
   };

This isn't catched by my patch. I will dig deeper to check where is the problem

http://reviews.llvm.org/D5409