[Sema] Disallow __make_integer_seq from showing up in __make_integer_seq

We hit over stringent asserts when trying to diagnose.  Loosen them as
appropriate.

This fixes PR28494.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@275047 91177308-0d34-0410-b5e6-96231b3b80d8

Author: majnemer

lib/Sema/SemaTemplate.cpp

@@ -5378,11 +5378,13 @@ bool Sema::CheckTemplateArgument(TemplateTemplateParmDecl *Param,
   if (!isa<ClassTemplateDecl>(Template) &&
       !isa<TemplateTemplateParmDecl>(Template) &&
       !isa<TypeAliasTemplateDecl>(Template)) {
-    assert(isa<FunctionTemplateDecl>(Template) &&
-           "Only function templates are possible here");
+    assert((isa<FunctionTemplateDecl>(Template) ||
+            isa<BuiltinTemplateDecl>(Template)) &&
+           "Only function or builtin templates are possible here");
     Diag(Arg.getLocation(), diag::err_template_arg_not_valid_template);
-    Diag(Template->getLocation(), diag::note_template_arg_refers_here_func)
-      << Template;
+    if (isa<FunctionTemplateDecl>(Template))
+      Diag(Template->getLocation(), diag::note_template_arg_refers_here_func)
+          << Template;
   }
 
   TemplateParameterList *Params = Param->getTemplateParameters();

test/SemaCXX/make_integer_seq.cpp

@@ -47,3 +47,7 @@ using illformed2 = ErrorSeq<int, -5>;
 
 template <typename T, T N> void f() {}
 __make_integer_seq<f, int, 0> x; // expected-error{{template template parameter must be a class template or type alias template}}
+
+__make_integer_seq<__make_integer_seq, int, 10> PR28494; // expected-error{{does not refer to a class or alias template, or template template parameter}} expected-error{{different template parameters}}
+// expected-note@make_integer_seq.cpp:* {{template parameter has a different kind}}
+// expected-note@make_integer_seq.cpp:* {{previous template template parameter is here}}