Re: [PATCH] c++: Allow attributes on concepts - DR 2428

[Jason Merrill <jason@redhat.com>]

On 11/14/22 00:40, Jakub Jelinek wrote:
> Hi!
> 
> Working virtually out of Baker Island.
> 
> The following patch adds parsing of attributes to concept definition,
> allows deprecated attribute to be specified (some ugliness needed
> because CONCEPT_DECL is a cp/*.def attribute and so can't be mentioned
> in c-family/ directly; used what is used for objc method decls,
> an alternative would be a langhook)

Several of the codes in c-common.def are C++-only, you might just move 
it over?

> and checks TREE_DEPRECATED in
> build_standard_check (not sure if that is the right spot, or whether
> it shouldn't be checked also for variable and function concepts and
> how to write testcase coverage for that).

I wouldn't bother with var/fn concepts, they're obsolete.

> Lightly tested so far.
> 
> 2022-11-13  Jakub Jelinek  <jakub@redhat.com>
> 
> gcc/c-family/
> 	* c-common.h (c_concept_decl): Declare.
> 	* c-attribs.cc (handle_deprecated_attribute): Allow deprecated
> 	attribute on CONCEPT_DECL if flag_concepts.
> gcc/c/
> 	* c-decl.cc (c_concept_decl): New function.
> gcc/cp/
> 	* cp-tree.h (finish_concept_definition): Add ATTRS parameter.
> 	* parser.cc (cp_parser_concept_definition): Parse attributes in
> 	between identifier and =.  Adjust finish_concept_definition
> 	caller.
> 	* pt.cc (finish_concept_definition): Add ATTRS parameter.  Call
> 	cplus_decl_attributes.
> 	* constraint.cc (build_standard_check): If CONCEPT_DECL is
> 	TREE_DEPRECATED, emit -Wdeprecated-declaration warnings.
> 	* tree.cc (c_concept_decl): New function.
> gcc/testsuite/
> 	* g++.dg/cpp2a/concepts-dr2428.C: New test.
> 
> --- gcc/c-family/c-common.h.jj	2022-10-27 21:00:53.698247586 -1200
> +++ gcc/c-family/c-common.h	2022-11-13 21:49:37.934598359 -1200
> @@ -831,6 +831,7 @@ extern tree (*make_fname_decl) (location
>   
>   /* In c-decl.cc and cp/tree.cc.  FIXME.  */
>   extern void c_register_addr_space (const char *str, addr_space_t as);
> +extern bool c_concept_decl (enum tree_code);
>   
>   /* In c-common.cc.  */
>   extern bool in_late_binary_op;
> --- gcc/c-family/c-attribs.cc.jj	2022-10-09 19:31:57.177988375 -1200
> +++ gcc/c-family/c-attribs.cc	2022-11-13 21:52:37.920152731 -1200
> @@ -4211,7 +4211,8 @@ handle_deprecated_attribute (tree *node,
>   	  || VAR_OR_FUNCTION_DECL_P (decl)
>   	  || TREE_CODE (decl) == FIELD_DECL
>   	  || TREE_CODE (decl) == CONST_DECL
> -	  || objc_method_decl (TREE_CODE (decl)))
> +	  || objc_method_decl (TREE_CODE (decl))
> +	  || (flag_concepts && c_concept_decl (TREE_CODE (decl))))
>   	TREE_DEPRECATED (decl) = 1;
>         else if (TREE_CODE (decl) == LABEL_DECL)
>   	{
> --- gcc/c/c-decl.cc.jj	2022-11-12 23:29:08.181504470 -1200
> +++ gcc/c/c-decl.cc	2022-11-13 21:50:38.178779716 -1200
> @@ -12987,6 +12987,14 @@ c_register_addr_space (const char *word,
>     ridpointers [rid] = id;
>   }
>   
> +/* C doesn't have CONCEPT_DECL.  */
> +
> +bool
> +c_concept_decl (enum tree_code)
> +{
> +  return false;
> +}
> +
>   /* Return identifier to look up for omp declare reduction.  */
>   
>   tree
> --- gcc/cp/cp-tree.h.jj	2022-11-11 20:30:10.138056914 -1200
> +++ gcc/cp/cp-tree.h	2022-11-13 20:58:39.443218815 -1200
> @@ -8324,7 +8324,7 @@ struct diagnosing_failed_constraint
>   extern cp_expr finish_constraint_or_expr	(location_t, cp_expr, cp_expr);
>   extern cp_expr finish_constraint_and_expr	(location_t, cp_expr, cp_expr);
>   extern cp_expr finish_constraint_primary_expr	(cp_expr);
> -extern tree finish_concept_definition		(cp_expr, tree);
> +extern tree finish_concept_definition		(cp_expr, tree, tree);
>   extern tree combine_constraint_expressions      (tree, tree);
>   extern tree append_constraint			(tree, tree);
>   extern tree get_constraints                     (const_tree);
> --- gcc/cp/parser.cc.jj	2022-11-08 22:39:13.325041007 -1200
> +++ gcc/cp/parser.cc	2022-11-13 20:58:15.692542640 -1200
> @@ -29672,6 +29672,8 @@ cp_parser_concept_definition (cp_parser
>         return NULL_TREE;
>       }
>   
> +  tree attrs = cp_parser_attributes_opt (parser);
> +
>     if (!cp_parser_require (parser, CPP_EQ, RT_EQ))
>       {
>         cp_parser_skip_to_end_of_statement (parser);
> @@ -29688,7 +29690,7 @@ cp_parser_concept_definition (cp_parser
>        but continue as if it were.  */
>     cp_parser_consume_semicolon_at_end_of_statement (parser);
>   
> -  return finish_concept_definition (id, init);
> +  return finish_concept_definition (id, init, attrs);
>   }
>   
>   // -------------------------------------------------------------------------- //
> --- gcc/cp/pt.cc.jj	2022-11-07 20:54:37.341399829 -1200
> +++ gcc/cp/pt.cc	2022-11-13 21:01:18.333053377 -1200
> @@ -29027,7 +29027,7 @@ placeholder_type_constraint_dependent_p
>      the TEMPLATE_DECL. */
>   
>   tree
> -finish_concept_definition (cp_expr id, tree init)
> +finish_concept_definition (cp_expr id, tree init, tree attrs)
>   {
>     gcc_assert (identifier_p (id));
>     gcc_assert (processing_template_decl);
> @@ -29061,6 +29061,9 @@ finish_concept_definition (cp_expr id, t
>     DECL_CONTEXT (decl) = current_scope ();
>     DECL_INITIAL (decl) = init;
>   
> +  if (attrs)
> +    cplus_decl_attributes (&decl, attrs, 0);
> +
>     set_originating_module (decl, false);
>   
>     /* Push the enclosing template.  */
> --- gcc/cp/constraint.cc.jj	2022-11-04 05:11:41.491946435 -1200
> +++ gcc/cp/constraint.cc	2022-11-13 22:24:55.314809969 -1200
> @@ -1396,6 +1396,8 @@ build_standard_check (tree tmpl, tree ar
>   {
>     gcc_assert (standard_concept_p (tmpl));
>     gcc_assert (TREE_CODE (tmpl) == TEMPLATE_DECL);
> +  if (TREE_DEPRECATED (DECL_TEMPLATE_RESULT (tmpl)))
> +    warn_deprecated_use (DECL_TEMPLATE_RESULT (tmpl), NULL_TREE);
>     tree parms = INNERMOST_TEMPLATE_PARMS (DECL_TEMPLATE_PARMS (tmpl));
>     args = coerce_template_parms (parms, args, tmpl, complain);
>     if (args == error_mark_node)
> --- gcc/cp/tree.cc.jj	2022-11-08 22:39:13.318041103 -1200
> +++ gcc/cp/tree.cc	2022-11-13 21:51:21.851186254 -1200
> @@ -6103,6 +6103,14 @@ c_register_addr_space (const char * /*wo
>   {
>   }
>   
> +/* Return true if CODE is CONCEPT_DECL.  */
> +
> +bool
> +c_concept_decl (enum tree_code code)
> +{
> +  return code == CONCEPT_DECL;
> +}
> +
>   /* Return the number of operands in T that we care about for things like
>      mangling.  */
>   
> --- gcc/testsuite/g++.dg/cpp2a/concepts-dr2428.C.jj	2022-11-13 22:27:56.977337907 -1200
> +++ gcc/testsuite/g++.dg/cpp2a/concepts-dr2428.C	2022-11-13 22:28:07.767191065 -1200
> @@ -0,0 +1,22 @@
> +// DR 2428
> +// { dg-do compile { target c++20 } }
> +
> +template<typename T>
> +concept C1 [[deprecated]] = true;
> +
> +template<typename T>
> +concept C2 __attribute__((deprecated)) = false;
> +
> +template<typename T>
> +concept C3 [[deprecated]] = true;
> +
> +template<typename T>
> +concept C4 __attribute__((deprecated)) = false;
> +
> +static_assert(C3<int>);	// { dg-warning "'C3' is deprecated" }
> +static_assert(C4<int>); // { dg-error "static assertion failed" }
> +			// { dg-warning "'C4' is deprecated" "" { target *-*-* } .-1 }
> +
> +template<typename T>
> +  requires C3<T>	// { dg-warning "'C3' is deprecated" }
> +int fn1(T t) { return 0; }
> 
> 	Jakub
>