[gcc r14-9033] c++: Diagnose this specifier on template parameters [PR113929]

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:5286b0761b5dfac4348d1c5bfdcc162a66f338ee

commit r14-9033-g5286b0761b5dfac4348d1c5bfdcc162a66f338ee
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Feb 16 17:42:32 2024 +0100

    c++: Diagnose this specifier on template parameters [PR113929]
    
    For template parameters, the optional this specifier is in the grammar
    template-parameter-list -> template-parameter -> parameter-declaration,
    just [dcl.fct/6] says that it is only valid in parameter-list of certain
    functions.  So, unlike the case of decl-specifier-seq used in non-terminals
    other than parameter-declaration, I think it is better not to fix this
    by
       cp_parser_decl_specifier_seq (parser,
    -                                flags | CP_PARSER_FLAGS_PARAMETER,
    +                                flags | (template_parameter_p ? 0
    +                                         : CP_PARSER_FLAGS_PARAMETER),
                                     &decl_specifiers,
                                     &declares_class_or_enum);
    which would be pretending it isn't in the grammar, but by diagnosing it
    separately, which is what the following patch does.
    
    2024-02-16  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/113929
            * parser.cc (cp_parser_parameter_declaration): Diagnose this specifier
            on template parameter declaration.
    
            * g++.dg/parse/pr113929.C: New test.

Diff:
---
 gcc/cp/parser.cc                      | 9 ++++++++-
 gcc/testsuite/g++.dg/parse/pr113929.C | 7 +++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 9d0914435fb1..b2ed2baa3a57 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -25724,8 +25724,15 @@ cp_parser_parameter_declaration (cp_parser *parser,
      for a C-style variadic function. */
   token = cp_lexer_peek_token (parser->lexer);
 
-  bool const xobj_param_p
+  bool xobj_param_p
     = decl_spec_seq_has_spec_p (&decl_specifiers, ds_this);
+  if (xobj_param_p && template_parm_p)
+    {
+      error_at (decl_specifiers.locations[ds_this],
+		"%<this%> specifier in template parameter declaration");
+      xobj_param_p = false;
+      decl_specifiers.locations[ds_this] = 0;
+    }
 
   if (xobj_param_p
       && ((declarator && declarator->parameter_pack_p)
diff --git a/gcc/testsuite/g++.dg/parse/pr113929.C b/gcc/testsuite/g++.dg/parse/pr113929.C
new file mode 100644
index 000000000000..4410f7bf85a7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/pr113929.C
@@ -0,0 +1,7 @@
+// PR c++/113929
+// { dg-do compile }
+
+template <this int C>		// { dg-error "'this' specifier in template parameter declaration" }
+struct S {};
+template <int N, this int C>	// { dg-error "'this' specifier in template parameter declaration" }
+struct T {};