Better diagnostics for covariance when checking overriding return types.

llvm-svn: 71786

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -307,6 +307,24 @@ def err_different_return_type_for_overriding_virtual_function : Error<
 def note_overridden_virtual_function : Note<
   "overridden virtual function is here">;
 
+def err_covariant_return_inaccessible_base : Error<
+  "return type of virtual function %2 is not covariant with the return type "
+  "of the function it overrides "
+  "(conversion from %0 to inaccessible base class %1)">;
+def err_covariant_return_ambiguous_derived_to_base_conv : Error<
+  "return type of virtual function %3 is not covariant with the return type of "
+  "the function it overrides (ambiguous conversion from derived class "
+  "%0 to base class %1:%2)">;
+def err_covariant_return_not_derived : Error<
+  "return type of virtual function %0 is not covariant with the return type of "
+  "the function it overrrides (%1 is not derived from %2)">;
+def err_covariant_return_type_different_qualifications : Error<
+  "return type of virtual function %0 is not covariant with the return type of "
+  "the function it overrides (%1 has different qualifiers than %2)">;
+def err_covariant_return_type_class_type_more_qualified : Error<
+  "return type of virtual function %0 is not covariant with the return type of "
+  "the function it overrides (class type %1 is more qualified than class "
+  "type %2">;
 // C++ constructors
 def err_constructor_cannot_be : Error<"constructor cannot be declared '%0'">;
 def err_invalid_qualified_constructor : Error<

clang/lib/Sema/SemaDeclCXX.cpp

@@ -2701,12 +2701,71 @@ bool Sema::CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
       CNewTy.getCVRQualifiers() == COldTy.getCVRQualifiers())
     return false;
   
-  // FIXME: Check covariance.
+  // Check if the return types are covariant
+  QualType NewClassTy, OldClassTy;
+  
+  /// Both types must be pointers or references to classes.
+  if (PointerType *NewPT = dyn_cast<PointerType>(NewTy)) {
+    if (PointerType *OldPT = dyn_cast<PointerType>(OldTy)) {
+      NewClassTy = NewPT->getPointeeType();
+      OldClassTy = OldPT->getPointeeType();
+    }
+  } else if (ReferenceType *NewRT = dyn_cast<ReferenceType>(NewTy)) {
+    if (ReferenceType *OldRT = dyn_cast<ReferenceType>(OldTy)) {
+      NewClassTy = NewRT->getPointeeType();
+      OldClassTy = OldRT->getPointeeType();
+    }
+  }
+  
+  // The return types aren't either both pointers or references to a class type.
+  if (NewClassTy.isNull()) {
+    Diag(New->getLocation(), 
+         diag::err_different_return_type_for_overriding_virtual_function)
+      << New->getDeclName() << NewTy << OldTy;
+    Diag(Old->getLocation(), diag::note_overridden_virtual_function);
+    
+    return true;
+  }
 
-  Diag(New->getLocation(), 
-       diag::err_different_return_type_for_overriding_virtual_function)
+  if (NewClassTy.getUnqualifiedType() != OldClassTy.getUnqualifiedType()) {
+    // Check if the new class derives from the old class.
+    if (!IsDerivedFrom(NewClassTy, OldClassTy)) {
+      Diag(New->getLocation(),
+           diag::err_covariant_return_not_derived)
+      << New->getDeclName() << NewTy << OldTy;
+      Diag(Old->getLocation(), diag::note_overridden_virtual_function);
+      return true;
+    }
+    
+    // Check if we the conversion from derived to base is valid.
+    if (CheckDerivedToBaseConversion(NewClassTy, OldClassTy, 
+                      diag::err_covariant_return_inaccessible_base,
+                      diag::err_covariant_return_ambiguous_derived_to_base_conv,
+                      // FIXME: Should this point to the return type?
+                      New->getLocation(), SourceRange(), New->getDeclName())) {
+      Diag(Old->getLocation(), diag::note_overridden_virtual_function);
+      return true;
+    }
+  }
+  
+  // The qualifiers of the return types must be the same.
+  if (CNewTy.getCVRQualifiers() != COldTy.getCVRQualifiers()) {
+    Diag(New->getLocation(),
+         diag::err_covariant_return_type_different_qualifications)
     << New->getDeclName() << NewTy << OldTy;
-  Diag(Old->getLocation(), diag::note_overridden_virtual_function);
-       
-  return true;
+    Diag(Old->getLocation(), diag::note_overridden_virtual_function);
+    return true;
+  };
+  
+
+  // The new class type must have the same or less qualifiers as the old type.
+  if (NewClassTy.isMoreQualifiedThan(OldClassTy)) {
+    Diag(New->getLocation(),
+         diag::err_covariant_return_type_class_type_more_qualified)
+    << New->getDeclName() << NewTy << OldTy;
+    Diag(Old->getLocation(), diag::note_overridden_virtual_function);
+    return true;
+  };
+  
+  return false;
 }

clang/test/SemaCXX/virtual-override.cpp

@@ -1,4 +1,4 @@
-// RUN: clang-cc -fsyntax-only -verify %s
+// RUN: clang-cc -fsyntax-only -faccess-control -verify %s
 
 namespace T1 {
 
@@ -11,3 +11,83 @@ class B : A {
 };
 
 }
+
+namespace T2 {
+
+struct a { };
+struct b { };
+  
+class A {
+  virtual a* f(); // expected-note{{overridden virtual function is here}}
+};
+
+class B : A {
+  virtual b* f(); // expected-error{{return type of virtual function 'f' is not covariant with the return type of the function it overrrides ('struct T2::b *' is not derived from 'struct T2::a *')}}
+};
+
+}
+
+namespace T3 {
+
+struct a { };
+struct b : private a { }; // expected-note{{'private' inheritance specifier here}}
+  
+class A {
+  virtual a* f(); // expected-note{{overridden virtual function is here}}
+};
+
+class B : A {
+  virtual b* f(); // expected-error{{return type of virtual function 'f' is not covariant with the return type of the function it overrides (conversion from 'struct T3::b' to inaccessible base class 'struct T3::a')}}
+};
+
+}
+
+namespace T4 {
+
+struct a { };
+struct a1 : a { };
+struct b : a, a1 { };
+  
+class A {
+  virtual a* f(); // expected-note{{overridden virtual function is here}}
+};
+
+class B : A {
+  virtual b* f(); // expected-error{{return type of virtual function 'f' is not covariant with the return type of the function it overrides (ambiguous conversion from derived class 'struct T4::b' to base class 'struct T4::a':\n\
+    struct T4::b -> struct T4::a\n\
+    struct T4::b -> struct T4::a1 -> struct T4::a)}}
+};
+
+}
+
+namespace T5 {
+  
+struct a { };
+
+class A {
+  virtual a* const f(); 
+  virtual a* const g(); // expected-note{{overridden virtual function is here}}
+};
+
+class B : A {
+  virtual a* const f(); 
+  virtual a* g(); // expected-error{{return type of virtual function 'g' is not covariant with the return type of the function it overrides ('struct T5::a *' has different qualifiers than 'struct T5::a *const')}}
+};
+
+}
+
+namespace T6 {
+  
+struct a { };
+
+class A {
+  virtual const a* f(); 
+  virtual a* g(); // expected-note{{overridden virtual function is here}}
+};
+
+class B : A {
+  virtual a* f(); 
+  virtual const a* g(); // expected-error{{return type of virtual function 'g' is not covariant with the return type of the function it overrides (class type 'struct T6::a const *' is more qualified than class type 'struct T6::a *'}}
+};
+
+}