[Sema] Avoid using a null type pointer (fixes PR32750)

[vsk]

Summary

isMicrosoftMissingTypename() uses a Type pointer without first checking
that it's non-null. PR32750 reports a case where the pointer is in fact
null. This patch adds in a defensive check and a regression test.

[nikola]

LGTM

test/SemaCXX/MicrosoftExtensions.cpp

516

nitpick: you don't need the space between angle brackets since you set the standard to C++14, I'm not sure what the convention here is but you don't need more than C++11...

[vsk]

test/SemaCXX/MicrosoftExtensions.cpp

516

Thanks for taking a look! I'll fix this up before committing.

lib/Sema/SemaDecl.cpp

bool Sema::isMicrosoftMissingTypename(const CXXScopeSpec *SS, Scope *S) {
   if (CurContext->isRecord()) {
     if (SS->getScopeRep()->getKind() == NestedNameSpecifier::Super)
       return true;
 
     const Type *Ty = SS->getScopeRep()->getAsType();
 
     CXXRecordDecl *RD = cast<CXXRecordDecl>(CurContext);
     for (const auto &Base : RD->bases())
-      if (Context.hasSameUnqualifiedType(QualType(Ty, 1), Base.getType()))
+      if (Ty && Context.hasSameUnqualifiedType(QualType(Ty, 1), Base.getType()))
         return true;
     return S->isFunctionPrototypeScope();
   }
   return CurContext->isFunctionOrMethod() || S->isFunctionPrototypeScope();
 }
 
 void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
                                    SourceLocation IILoc,

test/SemaCXX/MicrosoftExtensions.cpp

 // RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -Wmicrosoft -Wc++11-extensions -Wno-long-long -verify -fms-extensions -fexceptions -fcxx-exceptions -DTEST1
 // RUN: %clang_cc1 -std=c++98 %s -triple i686-pc-win32 -fsyntax-only -Wmicrosoft -Wc++11-extensions -Wno-long-long -verify -fms-extensions -fexceptions -fcxx-exceptions -DTEST1
 // RUN: %clang_cc1 -std=c++11 %s -triple i686-pc-win32 -fsyntax-only -Wmicrosoft -Wc++11-extensions -Wno-long-long -verify -fms-extensions -fexceptions -fcxx-exceptions -DTEST1
 // RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -Wmicrosoft -Wc++11-extensions -Wno-long-long -verify -fexceptions -fcxx-exceptions -DTEST2
+// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -std=c++14 -fms-compatibility -verify -DTEST3
 
 #if TEST1
 
 // Microsoft doesn't validate exception specification.
 namespace microsoft_exception_spec {
 
 void foo(); // expected-note {{previous declaration}}
 void foo() throw(); // expected-warning {{exception specification in declaration does not match previous declaration}}

 int S::fn() { return 0; } // expected-warning {{is missing exception specification}}
 }
 
 #elif TEST2
 
 // Check that __unaligned is not recognized if MS extensions are not enabled
 typedef char __unaligned *aligned_type; // expected-error {{expected ';' after top level declarator}}
 
+#elif TEST3
+
+namespace PR32750 {
+template<typename T> struct A {};
+template<typename T> struct B : A<A<T> > { A<T>::C::D d; }; // expected-error {{missing 'typename' prior to dependent type name 'A<T>::C::D'}}
+}
+
 #else
 
 #error Unknown test mode
 
 #endif