c++: Fix up parameter pack diagnostics on xobj vs. varargs functions [PR113802]

The simple presence of ellipsis as next token after the parameter
declaration doesn't imply it is a parameter pack, it sometimes is, e.g.
if its type is a pack, but sometimes is not and in that case it acts
the same as if the next tokens were , ... instead of just ...
The xobj param cannot be a function parameter pack though treats both
the declarator->parameter_pack_p and token->type == CPP_ELLIPSIS as
sufficient conditions for the error.  The conditions for CPP_ELLIPSIS
are done a little bit later in the same function and complex enough that
IMHO shouldn't be repeated, on the other side for the
declarator->parameter_pack_p case we clear that flag for xobj params
for error recovery reasons.

This patch just moves the diagnostics later (after the CPP_ELLIPSIS handling)
and changes the error recovery behavior by pretending the this specifier
didn't appear if an error is reported.

2024-03-08  Jakub Jelinek  <jakub@redhat.com>

	PR c++/113802
	* parser.cc (cp_parser_parameter_declaration): Move the xobj_param_p
	pack diagnostics after ellipsis handling and if an error is reported,
	pretend this specifier didn't appear.  Formatting fix.

	* g++.dg/cpp23/explicit-obj-diagnostics3.C (S0, S1, S2, S3, S4): Don't
	expect any diagnostics on f and fd member function templates, add
	similar templates with ...Selves instead of Selves as k and kd and
	expect diagnostics for those.  Expect extra diagnostics in error
	recovery for g and gd member function templates.

1 files changed, 19 insertions, 19 deletions

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index e32acfc..bc3aa9d 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -25734,22 +25734,6 @@ cp_parser_parameter_declaration (cp_parser *parser,
       decl_specifiers.locations[ds_this] = 0;
     }
 
-  if (xobj_param_p
-      && ((declarator && declarator->parameter_pack_p)
-	  || cp_lexer_next_token_is (parser->lexer, CPP_ELLIPSIS)))
-    {
-      location_t xobj_param
-	= make_location (decl_specifiers.locations[ds_this],
-			 decl_spec_token_start->location,
-			 input_location);
-      error_at (xobj_param,
-		"an explicit object parameter cannot "
-		"be a function parameter pack");
-      /* Suppress errors that occur down the line.  */
-      if (declarator)
-	declarator->parameter_pack_p = false;
-    }
-
   /* If a function parameter pack was specified and an implicit template
      parameter was introduced during cp_parser_parameter_declaration,
      change any implicit parameters introduced into packs.  */
@@ -25762,9 +25746,10 @@ cp_parser_parameter_declaration (cp_parser *parser,
 	(INNERMOST_TEMPLATE_PARMS (current_template_parms));
 
       if (latest_template_parm_idx != template_parm_idx)
-	decl_specifiers.type = convert_generic_types_to_packs
-	  (decl_specifiers.type,
-	   template_parm_idx, latest_template_parm_idx);
+	decl_specifiers.type
+	  = convert_generic_types_to_packs (decl_specifiers.type,
+					    template_parm_idx,
+					    latest_template_parm_idx);
     }
 
   if (cp_lexer_next_token_is (parser->lexer, CPP_ELLIPSIS))
@@ -25794,6 +25779,21 @@ cp_parser_parameter_declaration (cp_parser *parser,
 	}
     }
 
+  if (xobj_param_p
+      && (declarator ? declarator->parameter_pack_p
+		     : PACK_EXPANSION_P (decl_specifiers.type)))
+    {
+      location_t xobj_param
+	= make_location (decl_specifiers.locations[ds_this],
+			 decl_spec_token_start->location,
+			 input_location);
+      error_at (xobj_param,
+		"an explicit object parameter cannot "
+		"be a function parameter pack");
+      xobj_param_p = false;
+      decl_specifiers.locations[ds_this] = 0;
+    }
+
   /* The restriction on defining new types applies only to the type
      of the parameter, not to the default argument.  */
   parser->type_definition_forbidden_message = saved_message;