Re: [PATCH] c++, v2: Allow attributes on concepts - DR 2428

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Nov 15, 2022 at 09:54:00AM +0100, Jakub Jelinek via Gcc-patches wrote:
> On Mon, Nov 14, 2022 at 07:00:54PM -0500, Jason Merrill wrote:
> > > 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.
> 
> Ok, so like this?
> The previous version passed bootstrap/regtest on x86_64-linux and i686-linux,
> I'll of course test this one as well.

Better with a patch.  Sorry.

2022-11-15  Jakub Jelinek  <jakub@redhat.com>

gcc/c-family/
	* c-common.def (CONCEPT_DECL): New tree, moved here from
	cp-tree.def.
	* c-common.cc (c_common_init_ts): Handle CONCEPT_DECL.
	* c-attribs.cc (handle_deprecated_attribute): Allow deprecated
	attribute on CONCEPT_DECL.
gcc/cp/
	* cp-tree.def (CONCEPT_DECL): Move to c-common.def.
	* cp-objcp-common.cc (cp_common_init_ts): Don't handle CONCEPT_DECL
	here.
	* 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.
gcc/testsuite/
	* g++.dg/cpp2a/concepts-dr2428.C: New test.

--- gcc/c-family/c-common.def.jj	2022-10-14 09:28:27.975164491 +0200
+++ gcc/c-family/c-common.def	2022-11-15 09:34:01.384591076 +0100
@@ -81,6 +81,14 @@ DEFTREECODE (CONTINUE_STMT, "continue_st
    SWITCH_STMT_SCOPE, respectively.  */
 DEFTREECODE (SWITCH_STMT, "switch_stmt", tcc_statement, 4)
 
+/* Extensions for C++ Concepts. */
+
+/* Concept definition. This is not entirely different than a VAR_DECL
+   except that a) it must be a template, and b) doesn't have the wide
+   range of value and linkage options available to variables.  Used
+   by C++ FE and in c-family attribute handling.  */
+DEFTREECODE (CONCEPT_DECL, "concept_decl", tcc_declaration, 0)
+
 /*
 Local variables:
 mode:c
--- gcc/c-family/c-common.cc.jj	2022-11-13 12:29:08.165504692 +0100
+++ gcc/c-family/c-common.cc	2022-11-15 09:34:48.828950083 +0100
@@ -8497,6 +8497,8 @@ c_common_init_ts (void)
   MARK_TS_EXP (FOR_STMT);
   MARK_TS_EXP (SWITCH_STMT);
   MARK_TS_EXP (WHILE_STMT);
+
+  MARK_TS_DECL_COMMON (CONCEPT_DECL);
 }
 
 /* Build a user-defined numeric literal out of an integer constant type VALUE
--- gcc/c-family/c-attribs.cc.jj	2022-11-14 13:35:34.184160348 +0100
+++ gcc/c-family/c-attribs.cc	2022-11-15 09:30:57.370081060 +0100
@@ -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))
+	  || TREE_CODE (decl) == CONCEPT_DECL)
 	TREE_DEPRECATED (decl) = 1;
       else if (TREE_CODE (decl) == LABEL_DECL)
 	{
--- gcc/cp/cp-tree.def.jj	2022-09-29 18:11:34.836666800 +0200
+++ gcc/cp/cp-tree.def	2022-11-15 09:32:17.456996090 +0100
@@ -495,11 +495,6 @@ DEFTREECODE (OMP_DEPOBJ, "omp_depobj", t
 
 /* Extensions for Concepts. */
 
-/* Concept definition. This is not entirely different than a VAR_DECL
-   except that a) it must be a template, and b) doesn't have the wide
-   range of value and linkage options available to variables.  */
-DEFTREECODE (CONCEPT_DECL, "concept_decl", tcc_declaration, 0)
-
 /* Used to represent information associated with constrained declarations. */
 DEFTREECODE (CONSTRAINT_INFO, "constraint_info", tcc_exceptional, 0)
 
--- gcc/cp/cp-objcp-common.cc.jj	2022-09-30 18:38:55.349607203 +0200
+++ gcc/cp/cp-objcp-common.cc	2022-11-15 09:34:21.963313049 +0100
@@ -473,7 +473,6 @@ cp_common_init_ts (void)
   /* New decls.  */
   MARK_TS_DECL_COMMON (TEMPLATE_DECL);
   MARK_TS_DECL_COMMON (WILDCARD_DECL);
-  MARK_TS_DECL_COMMON (CONCEPT_DECL);
 
   MARK_TS_DECL_NON_COMMON (USING_DECL);
 
--- gcc/cp/cp-tree.h.jj	2022-11-15 08:17:07.561388452 +0100
+++ gcc/cp/cp-tree.h	2022-11-15 09:30:57.371081046 +0100
@@ -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	2022-11-14 13:35:34.380157682 +0100
+++ gcc/cp/parser.cc	2022-11-15 09:30:57.377080965 +0100
@@ -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/constraint.cc.jj	2022-11-14 13:35:34.269159192 +0100
+++ gcc/cp/constraint.cc	2022-11-15 09:30:57.382080897 +0100
@@ -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/pt.cc.jj	2022-11-15 07:56:05.130350281 +0100
+++ gcc/cp/pt.cc	2022-11-15 09:30:57.381080911 +0100
@@ -29030,7 +29030,7 @@ 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);
@@ -29064,6 +29064,9 @@ 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/testsuite/g++.dg/cpp2a/concepts-dr2428.C.jj	2022-11-15 09:30:57.382080897 +0100
+++ gcc/testsuite/g++.dg/cpp2a/concepts-dr2428.C	2022-11-15 09:30:57.382080897 +0100
@@ -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