[Sema] Make sure we substitute an instantiation-dependent default template parameter

[erik.pilkington]

Summary

Previously, we'd accept the attached test because we didn't substitute into void_t when we really ought to of.

Fixes llvm.org/PR39623

Thanks!

[Rakete1111]

LGTM, thanks :)

clang/test/SemaCXX/alias-template.cpp

188 ↗

(On Diff #173615)

Very nit: The whole file has a space between the expected string and {{.

cfe/trunk/lib/Sema/SemaTemplate.cpp

SubstDefaultTemplateArgument(Sema &SemaRef,
                              SourceLocation TemplateLoc,
                              SourceLocation RAngleLoc,
                              TemplateTypeParmDecl *Param,
                              SmallVectorImpl<TemplateArgument> &Converted) {
   TypeSourceInfo *ArgType = Param->getDefaultArgumentInfo();
 
   // If the argument type is dependent, instantiate it now based
   // on the previously-computed template arguments.
-  if (ArgType->getType()->isDependentType()) {
+  if (ArgType->getType()->isInstantiationDependentType()) {
     Sema::InstantiatingTemplate Inst(SemaRef, TemplateLoc,
                                      Param, Template, Converted,
                                      SourceRange(TemplateLoc, RAngleLoc));
     if (Inst.isInvalid())
       return nullptr;
 
     TemplateArgumentList TemplateArgs(TemplateArgumentList::OnStack, Converted);
 

cfe/trunk/test/SemaCXX/alias-template.cpp

 template <int I>
 struct S {
   template <int J>
   using T = X[J];
   using U = T<I>;
 };
 static_assert(__is_same(S<3>::U, X[2]), ""); // expected-error {{static_assert failed}}
 }
+
+namespace PR39623 {
+template <class T>
+using void_t = void;
+
+template <class T, class = void_t<typename T::wait_what>>
+int sfinae_me() { return 0; } // expected-note{{candidate template ignored: substitution failure}}
+
+int g = sfinae_me<int>(); // expected-error{{no matching function for call to 'sfinae_me'}}
+}