r370594 - [clang] Warning for non-final classes with final destructors

[David Bolvansky via cfe-commits]

Author: xbolva00
Date: Sat Aug 31 11:31:19 2019
New Revision: 370594

URL: http://llvm.org/viewvc/llvm-project?rev=370594&view=rev
Log:
[clang] Warning for non-final classes with final destructors

Marking a class' destructor final prevents the class from being inherited from. However, it is a subtle and awkward way to express that at best, and unintended at worst. It may also generate worse code (in other compilers) than marking the class itself final. For these reasons, this revision adds a warning for nonfinal classes with final destructors, with a note to suggest marking the class final to silence the warning.

See https://reviews.llvm.org/D66621 for more background.

Patch by logan-5 (Logan Smith)

Differential Revision: https://reviews.llvm.org/D66711

Added:
    cfe/trunk/test/SemaCXX/warn-final-dtor-non-final-class.cpp
Modified:
    cfe/trunk/lib/Sema/SemaDeclCXX.cpp
    cfe/trunk/test/SemaCXX/MicrosoftExtensions.cpp

Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclCXX.cpp?rev=370594&r1=370593&r2=370594&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDeclCXX.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp Sat Aug 31 11:31:19 2019
@@ -6236,6 +6236,19 @@ void Sema::CheckCompletedCXXClass(CXXRec
     }
   }
 
+  // Warn if the class has a final destructor but is not itself marked final.
+  if (!Record->hasAttr<FinalAttr>()) {
+    if (const CXXDestructorDecl *dtor = Record->getDestructor()) {
+      if (const FinalAttr *FA = dtor->getAttr<FinalAttr>()) {
+        Diag(FA->getLocation(), diag::warn_final_dtor_non_final_class)
+          << FA->isSpelledAsSealed();
+        Diag(Record->getLocation(), diag::note_final_dtor_non_final_class_silence)
+          << Context.getRecordType(Record)
+          << FA->isSpelledAsSealed();
+      }
+    }
+  }
+
   // See if trivial_abi has to be dropped.
   if (Record->hasAttr<TrivialABIAttr>())
     checkIllFormedTrivialABIStruct(*Record);

Modified: cfe/trunk/test/SemaCXX/MicrosoftExtensions.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/MicrosoftExtensions.cpp?rev=370594&r1=370593&r2=370594&view=diff
==============================================================================
--- cfe/trunk/test/SemaCXX/MicrosoftExtensions.cpp (original)
+++ cfe/trunk/test/SemaCXX/MicrosoftExtensions.cpp Sat Aug 31 11:31:19 2019
@@ -440,6 +440,11 @@ struct SealedType sealed : SomeBase {
 // expected-error at +1 {{base 'SealedType' is marked 'sealed'}}
 struct InheritFromSealed : SealedType {};
 
+class SealedDestructor { // expected-note {{mark 'SealedDestructor' as 'sealed' to silence this warning}}
+    // expected-warning at +1 {{'sealed' keyword is a Microsoft extension}}
+    virtual ~SealedDestructor() sealed; // expected-warning {{class with destructor marked 'sealed' cannot be inherited from}}
+};
+
 void AfterClassBody() {
   // expected-warning at +1 {{attribute 'deprecated' is ignored, place it after "struct" to apply attribute to type declaration}}
   struct D {} __declspec(deprecated);

Added: cfe/trunk/test/SemaCXX/warn-final-dtor-non-final-class.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-final-dtor-non-final-class.cpp?rev=370594&view=auto
==============================================================================
--- cfe/trunk/test/SemaCXX/warn-final-dtor-non-final-class.cpp (added)
+++ cfe/trunk/test/SemaCXX/warn-final-dtor-non-final-class.cpp Sat Aug 31 11:31:19 2019
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify %s -Wfinal-dtor-non-final-class
+
+class A {
+    ~A();
+};
+
+class B { // expected-note {{mark 'B' as 'final' to silence this warning}}
+    virtual ~B() final; // expected-warning {{class with destructor marked 'final' cannot be inherited from}}
+};
+
+class C final {
+    virtual ~C() final;
+};