[Concepts] Fix isDeclarationSpecifier to detect type-constraints correctly

isDeclarationSpecifiers did not handle some cases of placeholder-type-specifiers with
type-constraints, causing parsing bugs in abbreviated constructor templates.

Add comprehensive handling of type-constraints to isDeclarationSpecifier.

1 files changed, 8 insertions, 3 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 871ca25..af6e105 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -5061,6 +5061,8 @@ bool Parser::isDeclarationSpecifier(bool DisambiguatingWithExpression) {
     // recurse to handle whatever we get.
     if (TryAnnotateTypeOrScopeToken())
       return true;
+    if (TryAnnotateTypeConstraint())
+      return true;
     if (Tok.is(tok::identifier))
       return false;
 
@@ -5193,11 +5195,14 @@ bool Parser::isDeclarationSpecifier(bool DisambiguatingWithExpression) {
 
     // placeholder-type-specifier
   case tok::annot_template_id: {
-    TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
-    return TemplateId->Kind == TNK_Concept_template &&
+    return isTypeConstraintAnnotation() &&
         (NextToken().is(tok::kw_auto) || NextToken().is(tok::kw_decltype));
   }
-
+  case tok::annot_cxxscope:
+    if (NextToken().is(tok::identifier) && TryAnnotateTypeConstraint())
+      return true;
+    return isTypeConstraintAnnotation() &&
+        GetLookAheadToken(2).isOneOf(tok::kw_auto, tok::kw_decltype);
   case tok::kw___declspec:
   case tok::kw___cdecl:
   case tok::kw___stdcall: