Suppress -Wdelete-non-virtual-dtor warnings _about_ classes defined in system headers.

[thakis]

Summary

r312167 made it so that we emit Wdelete-non-virtual-dtor from delete statements that are in system headers (e.g. std::unique_ptr). That works great on Linux and macOS, but on Windows there are non-final classes that are defined in system headers that have virtual methods but non-virtual destructors and yet get deleted through a base class pointer (e.g. ATL::CAccessToken::CRevert). So paddle back a bit and don't emit the warning if it's about a class defined in a system header.

[rnk]

Lgtm

[thakis]

312216, thanks!

lib/Sema/SemaExprCXX.cpp

void Sema::CheckVirtualDtorCall(CXXDestructorDecl *dtor, SourceLocation Loc,
   //   deleted and the static type shall have a virtual destructor or the
   //   behavior is undefined.
   //
   const CXXRecordDecl *PointeeRD = dtor->getParent();
   // Note: a final class cannot be derived from, no issue there
   if (!PointeeRD->isPolymorphic() || PointeeRD->hasAttr<FinalAttr>())
     return;
 
+  // If the superclass is in a system header, there's nothing that can be done.
+  // The `delete` (where we emit the warning) can be in a system header,
+  // what matters for this warning is where the deleted type is defined.
+  if (getSourceManager().isInSystemHeaer(PointeeRD->getLocation()))
+    return;
+
   QualType ClassType = dtor->getThisType(Context)->getPointeeType();
   if (PointeeRD->isAbstract()) {
     // If the class is abstract, we warn by default, because we're
     // sure the code has undefined behavior.
     Diag(Loc, diag::warn_delete_abstract_non_virtual_dtor) << (IsDelete ? 0 : 1)
                                                            << ClassType;
   } else if (WarnOnNonAbstractTypes) {
     // Otherwise, if this is not an array delete, it's a bit suspect,

test/SemaCXX/destructor.cpp

 // RUN: %clang_cc1 -std=c++11 -triple %itanium_abi_triple -fsyntax-only -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -fcxx-exceptions -verify %s
 // RUN: %clang_cc1 -std=c++11 -triple %ms_abi_triple -DMSABI -fsyntax-only -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -verify %s
 
 #if defined(BE_THE_HEADER)
 
 // Wdelete-non-virtual-dtor should warn about the delete from smart pointer
 // classes in system headers (std::unique_ptr...) too.
 
 #pragma clang system_header
 namespace dnvd {
+
+struct SystemB {
+  virtual void foo();
+};
+
 template <typename T>
 class simple_ptr {
 public:
   simple_ptr(T* t): _ptr(t) {}
   ~simple_ptr() { delete _ptr; } // \
     // expected-warning {{delete called on non-final 'dnvd::B' that has virtual functions but non-virtual destructor}} \
     // expected-warning {{delete called on non-final 'dnvd::D' that has virtual functions but non-virtual destructor}}
   T& operator*() const { return *_ptr; }
void nowarn1() {
   {
     simple_ptr<VD> vd(new VD());
     use(*vd);
   }
   {
     simple_ptr<VF> vf(new VF());
     use(*vf);
   }
+  {
+    simple_ptr<SystemB> sb(new SystemB());
+    use(*sb);
+  }
+
 }
 
 void warn1() {
   {
     simple_ptr<B> b(new B()); // expected-note {{in instantiation of member function 'dnvd::simple_ptr<dnvd::B>::~simple_ptr' requested here}}
     use(*b);
   }
   {