[clang] invalidate a non-dependent-type RecordDecl when it has any dependent-type base class specifier.

[hokein]

Summary

This happens during the error-recovery, and it would esacpe all
dependent-type check guards in getTypeInfo/constexpr-evaluator code
paths, which lead to crashes.

clang/lib/Sema/SemaDeclCXX.cpp

if (CXXRecordDecl *BaseDecl = BaseType->getAsCXXRecordDecl()) {
         if (BaseDecl->getCanonicalDecl() != Class->getCanonicalDecl())
           Diag(BaseDecl->getLocation(), diag::note_previous_decl)
             << BaseType;
 
         return nullptr;
       }
     }
 
+    // Make sure that we don't make an ill-formed AST where the type of the
+    // Class is non-dependent and its attached base class specifier is an
+    // dependent type, which violates invariants in many clang code paths (e.g.
+    // constexpr evaluator). If this case happens (in errory-recovery mode), we
+    // explicitly mark the Class decl invalid. The diagnostic was already
+    // emitted.
+    if (!Class->getTypeForDecl()->isDependentType())
+      Class->setInvalidDecl();
     return new (Context) CXXBaseSpecifier(SpecifierRange, Virtual,
                                           Class->getTagKind() == TTK_Class,
                                           Access, TInfo, EllipsisLoc);
   }
 
   // Base specifiers must be record types.
   if (!BaseType->isRecordType()) {
     Diag(BaseLoc, diag::err_base_must_be_class) << SpecifierRange;

clang/test/SemaTemplate/temp_class_spec.cpp

 template <int Y>
 class Bar;
 
 template <typename Z>
 class Bar<0> : public Foo<Z> { // expected-error{{partial specialization of 'Bar' does not use any of its template parameters}}
   Bar() : Foo<Z>() {}
 };
 } // namespace
+
+namespace Crash {
+template<typename T>
+class Base {};
+
+template<typename T> class Foo;
+
+template <typename T>
+class Foo<int> : public Base<T> {}; // expected-error{{partial specialization of 'Foo' does not use any of its template parameters}}
+
+// verify that getASTRecordLayout doesn't crash on the ClassTemplateSpecializationDecl.
+constexpr int s = sizeof(Foo<int>);
+}