[Clang] Improve diagnostics when using a concept as template argument

When using the name of a template variable or concept in places
where an expression was expected, Clang would drop the cxxscope token
preceeding it, if any.

This leads to subpar diagnostics - complaining about the
identifier being undeclared as clang would not know to look into a
non-global scope.

We make sure the scope is preserved.

When encountering `ns::Concept foo x;`, Clang would also fail
to provide the same quality as it does at global scope.

Reviewed By: aaron.ballman, erichkeane

Differential Revision: https://reviews.llvm.org/D146719

1 files changed, 5 insertions, 5 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 2b5829b..91376cf 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -3448,12 +3448,12 @@ void Parser::ParseDeclarationSpecifiers(
         continue;
       }
 
-      if (TemplateId && TemplateId->Kind == TNK_Concept_template &&
-          GetLookAheadToken(2).isOneOf(tok::kw_auto, tok::kw_decltype)) {
+      if (TemplateId && TemplateId->Kind == TNK_Concept_template) {
         DS.getTypeSpecScope() = SS;
-        // This is a qualified placeholder-specifier, e.g., ::C<int> auto ...
-        // Consume the scope annotation and continue to consume the template-id
-        // as a placeholder-specifier.
+        // This is probably a qualified placeholder-specifier, e.g., ::C<int>
+        // auto ... Consume the scope annotation and continue to consume the
+        // template-id as a placeholder-specifier. Let the next iteration
+        // diagnose a missing auto.
         ConsumeAnnotationToken();
         continue;
       }