[gcc r13-1391] c++: add fixup to missing .template warning

[Jason Merrill]

https://gcc.gnu.org/g:288c6cce0277e03e08b324283b6a015a70066bb7

commit r13-1391-g288c6cce0277e03e08b324283b6a015a70066bb7
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jun 29 17:12:09 2022 -0400

    c++: add fixup to missing .template warning
    
    I experimented with giving this diagnostic in another place, which didn't
    work out, but we can still benefit from adding the fixup.
    
    gcc/cp/ChangeLog:
    
            * parser.cc (missing_template_diag): Split out...
            (cp_parser_id_expression): ...from here.

Diff:
---
 gcc/cp/parser.cc | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 357fde557c7..f6bc8db8581 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -6093,6 +6093,23 @@ cp_parser_primary_expression (cp_parser *parser,
 				       /*decltype*/false, idk);
 }
 
+/* Complain about missing template keyword when naming a dependent
+   member template.  */
+
+static void
+missing_template_diag (location_t loc, diagnostic_t diag_kind = DK_WARNING)
+{
+  if (warning_suppressed_at (loc, OPT_Wmissing_template_keyword))
+    return;
+
+  gcc_rich_location richloc (loc);
+  richloc.add_fixit_insert_before ("template");
+  emit_diagnostic (diag_kind, &richloc, OPT_Wmissing_template_keyword,
+		   "expected %qs keyword before dependent "
+		   "template name", "template");
+  suppress_warning_at (loc, OPT_Wmissing_template_keyword);
+}
+
 /* Parse an id-expression.
 
    id-expression:
@@ -6268,9 +6285,7 @@ cp_parser_id_expression (cp_parser *parser,
 	     operator.  */
 	  && (cp_lexer_peek_token (parser->lexer)->type
 	      <= CPP_LAST_PUNCTUATOR))
-	warning_at (token->location, OPT_Wmissing_template_keyword,
-		    "expected %qs keyword before dependent "
-		    "template name", "template");
+	missing_template_diag (token->location);
     }
 
   return id;