[clang] Add covariance tests that make sure we return an error when return value is different in pointer / lvalue ref / rvalue ref

Per https://cplusplus.github.io/CWG/issues/960.html.

Author: bricknerb

clang/test/SemaCXX/virtual-override.cpp

@@ -83,7 +83,7 @@ namespace T6 {
 struct a { };
 
 class A {
-  // Classes.
+  // Check cv-qualification.
   virtual const a* const_vs_unqualified_class();
   virtual a* unqualified_vs_const_class(); // expected-note{{overridden virtual function is here}}
 
@@ -102,13 +102,23 @@ class A {
   virtual const volatile a* const_volatile_vs_unualified_class();
   virtual a* unqualified_vs_const_volatile_class(); // expected-note{{overridden virtual function is here}}
 
-  // Non Classes.
+  // Check lvalue ref vs rvalue ref vs pointer.
+  virtual a& rvalue_ref();
+  virtual a&& lvalue_ref();
+  virtual a& rvalue_vs_lvalue_ref(); // expected-note{{overridden virtual function is here}}
+  virtual a&& lvalue_vs_rvalue_ref(); // expected-note{{overridden virtual function is here}}
+  virtual a& rvalue_ref_vs_pointer(); // expected-note{{overridden virtual function is here}}
+  virtual a* pointer_vs_rvalue_ref(); // expected-note{{overridden virtual function is here}}
+  virtual a&& lvalue_ref_vs_pointer(); // expected-note{{overridden virtual function is here}}
+  virtual a* pointer_vs_lvalue_ref(); // expected-note{{overridden virtual function is here}}
+
+  // Check non class.
   virtual const int* const_vs_unqualified_non_class(); // expected-note{{overridden virtual function is here}}
   virtual int* unqualified_vs_const_non_class(); // expected-note{{overridden virtual function is here}}
 };
 
 class B : A {
-  // Classes.
+  // Check cv-qualification.
   a* const_vs_unqualified_class() override;
   const a* unqualified_vs_const_class() override; // expected-error{{return type of virtual function 'unqualified_vs_const_class' is not covariant with the return type of the function it overrides (class type 'const a *' does not have the same cv-qualification as or less cv-qualification than class type 'a *')}}
 
@@ -127,7 +137,17 @@ class B : A {
   a* const_volatile_vs_unualified_class() override;
   const volatile a* unqualified_vs_const_volatile_class() override; // expected-error{{return type of virtual function 'unqualified_vs_const_volatile_class' is not covariant with the return type of the function it overrides (class type 'const volatile a *' does not have the same cv-qualification as or less cv-qualification than class type 'a *')}}
 
-  // Non Classes.
+  // Check lvalue ref vs rvalue ref vs pointer.
+  a& rvalue_ref() override;
+  a&& lvalue_ref() override;
+  a&& rvalue_vs_lvalue_ref() override; // expected-error{{virtual function 'rvalue_vs_lvalue_ref' has a different return type ('a &&') than the function it overrides (which has return type 'a &')}}
+  a& lvalue_vs_rvalue_ref() override; // expected-error{{virtual function 'lvalue_vs_rvalue_ref' has a different return type ('a &') than the function it overrides (which has return type 'a &&')}}
+  a* rvalue_ref_vs_pointer() override; // expected-error{{virtual function 'rvalue_ref_vs_pointer' has a different return type ('a *') than the function it overrides (which has return type 'a &')}}
+  a& pointer_vs_rvalue_ref() override; // expected-error{{virtual function 'pointer_vs_rvalue_ref' has a different return type ('a &') than the function it overrides (which has return type 'a *')}}
+  a* lvalue_ref_vs_pointer() override; // expected-error{{virtual function 'lvalue_ref_vs_pointer' has a different return type ('a *') than the function it overrides (which has return type 'a &&')}}
+  a&& pointer_vs_lvalue_ref() override; // expected-error{{virtual function 'pointer_vs_lvalue_ref' has a different return type ('a &&') than the function it overrides (which has return type 'a *')}}
+
+  // Check non class.
   int* const_vs_unqualified_non_class() override; // expected-error{{virtual function 'const_vs_unqualified_non_class' has a different return type ('int *') than the function it overrides (which has return type 'const int *')}}
   const int* unqualified_vs_const_non_class() override; // expected-error{{virtual function 'unqualified_vs_const_non_class' has a different return type ('const int *') than the function it overrides (which has return type 'int *')}}
 };