PR18733: Remove -Wweak-template-vtables

It isn't really pulling its weight and I think splitting it out from
-Wweak-vtables was the wrong call: I think it was just a bug in the
original warning, which was trying to not diagnose template
instantiations, implicit or explicit.

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1643,10 +1643,6 @@ def warn_weak_vtable : Warning<
   "%0 has no out-of-line virtual method definitions; its vtable will be "
   "emitted in every translation unit">,
   InGroup<DiagGroup<"weak-vtables">>, DefaultIgnore;
-def warn_weak_template_vtable : Warning<
-  "explicit template instantiation %0 will emit a vtable in every "
-  "translation unit">,
-  InGroup<DiagGroup<"weak-template-vtables">>, DefaultIgnore;
 
 def ext_using_undefined_std : ExtWarn<
   "using directive refers to implicitly-defined namespace 'std'">;

clang/lib/Sema/SemaDeclCXX.cpp

@@ -26,6 +26,7 @@
 #include "clang/AST/TypeOrdering.h"
 #include "clang/Basic/AttributeCommonInfo.h"
 #include "clang/Basic/PartialDiagnostic.h"
+#include "clang/Basic/Specifiers.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Lex/LiteralSupport.h"
 #include "clang/Lex/Preprocessor.h"
@@ -17647,16 +17648,12 @@ bool Sema::DefineUsedVTables() {
     // no key function or the key function is inlined. Don't warn in C++ ABIs
     // that lack key functions, since the user won't be able to make one.
     if (Context.getTargetInfo().getCXXABI().hasKeyFunctions() &&
-        Class->isExternallyVisible() && ClassTSK != TSK_ImplicitInstantiation) {
+        Class->isExternallyVisible() && ClassTSK != TSK_ImplicitInstantiation &&
+        ClassTSK != TSK_ExplicitInstantiationDefinition) {
       const FunctionDecl *KeyFunctionDef = nullptr;
       if (!KeyFunction || (KeyFunction->hasBody(KeyFunctionDef) &&
-                           KeyFunctionDef->isInlined())) {
-        Diag(Class->getLocation(),
-             ClassTSK == TSK_ExplicitInstantiationDefinition
-                 ? diag::warn_weak_template_vtable
-                 : diag::warn_weak_vtable)
-            << Class;
-      }
+                           KeyFunctionDef->isInlined()))
+        Diag(Class->getLocation(), diag::warn_weak_vtable) << Class;
     }
   }
   VTableUses.clear();

clang/test/SemaCXX/warn-weak-vtables.cpp

@@ -1,8 +1,8 @@
-// RUN: %clang_cc1 %s -fsyntax-only -verify -triple %itanium_abi_triple -Wweak-vtables -Wweak-template-vtables
+// RUN: %clang_cc1 %s -fsyntax-only -verify -triple %itanium_abi_triple -Wweak-vtables
 //
 // Check that this warning is disabled on MS ABI targets which don't have key
 // functions.
-// RUN: %clang_cc1 %s -fsyntax-only -triple %ms_abi_triple -Werror -Wweak-vtables -Wweak-template-vtables
+// RUN: %clang_cc1 %s -fsyntax-only -triple %ms_abi_triple -Werror -Wweak-vtables
 
 struct A { // expected-warning {{'A' has no out-of-line virtual method definitions; its vtable will be emitted in every translation unit}}
   virtual void f() { } 
@@ -63,7 +63,7 @@ template<typename T> struct TemplVirt {
   virtual void f();
 };
 
-template class TemplVirt<float>; // expected-warning{{explicit template instantiation 'TemplVirt<float>' will emit a vtable in every translation unit}}
+template class TemplVirt<float>;
 
 template<> struct TemplVirt<bool> {
   virtual void f();