[clang] [clang] When checking for covariant return types, make sure the poiners or references are to *classes* (PR #111856)

[Boaz Brickner via cfe-commits]

https://github.com/bricknerb updated https://github.com/llvm/llvm-project/pull/111856

>From 786d31e2657964e578cd1fdf2006b0fb3b19fab6 Mon Sep 17 00:00:00 2001
From: Boaz Brickner <brickner at google.com>
Date: Thu, 10 Oct 2024 15:15:23 +0000
Subject: [PATCH 1/3] [clang] When checking for covariant return types, make
 sure the pointers or references are to *classes*.

https://eel.is/c++draft/class.virtual#8.1

This prevents overriding methods with non class return types that have less cv-qualification.
---
 clang/lib/Sema/SemaDeclCXX.cpp          |  4 ++--
 clang/test/SemaCXX/virtual-override.cpp | 10 ++++++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 9cb2ed02a3f764..6195b62b8afa16 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -18273,7 +18273,7 @@ bool Sema::CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
   }
 
   // The return types aren't either both pointers or references to a class type.
-  if (NewClassTy.isNull()) {
+  if (NewClassTy.isNull() || !NewClassTy->isStructureOrClassType()) {
     Diag(New->getLocation(),
          diag::err_different_return_type_for_overriding_virtual_function)
         << New->getDeclName() << NewTy << OldTy
@@ -18296,7 +18296,7 @@ bool Sema::CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
                               diag::err_covariant_return_incomplete,
                               New->getDeclName()))
         return true;
-    }
+      }
 
     // Check if the new class derives from the old class.
     if (!IsDerivedFrom(New->getLocation(), NewClassTy, OldClassTy)) {
diff --git a/clang/test/SemaCXX/virtual-override.cpp b/clang/test/SemaCXX/virtual-override.cpp
index 72abfc3cf51e1f..6008b8ed063f20 100644
--- a/clang/test/SemaCXX/virtual-override.cpp
+++ b/clang/test/SemaCXX/virtual-override.cpp
@@ -289,3 +289,13 @@ namespace PR8168 {
     static void foo() {} // expected-error{{'static' member function 'foo' overrides a virtual function}}
   };
 }
+
+namespace T13 {
+  struct A {
+    virtual const int *f() const; // expected-note{{overridden virtual function is here}}
+  };
+
+  struct B : A {
+    int *f() const override; // expected-error{{virtual function 'f' has a different return type ('int *') than the function it overrides (which has return type 'const int *')}}
+  };
+}

>From 027a985f2ca2bbe007db751af4fdbb5d8f12959d Mon Sep 17 00:00:00 2001
From: Boaz Brickner <brickner at google.com>
Date: Fri, 11 Oct 2024 05:29:05 +0000
Subject: [PATCH 2/3] Fix indentation.

---
 clang/lib/Sema/SemaDeclCXX.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 6195b62b8afa16..75d010dc4e04d8 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -18296,7 +18296,7 @@ bool Sema::CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
                               diag::err_covariant_return_incomplete,
                               New->getDeclName()))
         return true;
-      }
+    }
 
     // Check if the new class derives from the old class.
     if (!IsDerivedFrom(New->getLocation(), NewClassTy, OldClassTy)) {

>From 0b0452f3b7206fdea595aff684c329fd4563f631 Mon Sep 17 00:00:00 2001
From: Boaz Brickner <brickner at google.com>
Date: Fri, 11 Oct 2024 12:27:00 +0000
Subject: [PATCH 3/3] [clang] Add the breaking change to more correctly check
 covariance when return type doesn't point to a class to release notes.

---
 clang/docs/ReleaseNotes.rst | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index df165b91252505..55ca61955c5b01 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -99,6 +99,19 @@ C++ Specific Potentially Breaking Changes
     // Was error, now evaluates to false.
     constexpr bool b = f() == g();
 
+- Clang will now correctly not consider pointers to non classes for covariance.
+
+  .. code-block:: c++
+
+  struct A {
+    virtual const int *f() const;
+  };
+  struct B : A {
+    // Return type has less cv-qualification but doesn't point to a class.
+    // Error will be generated.
+    int *f() const override;
+  };
+
 ABI Changes in This Version
 ---------------------------