Support C2x [[deprecated]] attribute.

This patch adds support for the C2x [[deprecated]] attribute.  All the
actual logic for generating warnings can be identical to the GNU
__attribute__ ((deprecated)), as can the attribute handler, so this is
just a matter of wiring things up appropriately and adding the checks
specified in the standard.  Unlike for C++, this patch gives
"deprecated" an entry in a table of standard attributes rather than
remapping it internally to the GNU attribute, as that seems a cleaner
approach to me.

Specifically, the only form of arguments to the attribute permitted in
the standard is (string-literal); empty parentheses are not permitted
in the case of no arguments, and a string literal (which includes
concatenated adjacent string literals, because concatenation is an
earlier phase of translation) cannot have further redundant
parentheses around it.  For the case of empty parentheses, this patch
makes the C parser disallow them for all known attributes using the
[[]] syntax, as done for C++.  For string literals (where the C++
front end is missing the check to avoid redundant parentheses, 92521
filed for that issue), a special case is inserted in the C parser.

A known issue that I think can be addressed later as a bug fix is that
the warnings for the attribute being ignored in certain cases
(attribute declarations, statements, most uses on types) ought to be
pedwarns, as those usages are constraint violations.

Bad handling of wide string literals with this attribute is also a
pre-existing bug (91182 - although that's filed as a C++ bug, the code
in question is language-independent, in tree.c).

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

gcc/c:
	* c-decl.c (std_attribute_table): New.
	(c_init_decl_processing): Register attributes from
	std_attribute_table.
	* c-parser.c (c_parser_attribute_arguments): Add arguments
	require_string and allow_empty_args.  All callers changed.
	(c_parser_std_attribute): Set require_string argument for
	"deprecated" attribute.

gcc/c-family:
	* c-attribs.c (handle_deprecated_attribute): Remove static.
	* c-common.h (handle_deprecated_attribute): Declare.

gcc/testsuite:
	* gcc.dg/c2x-attr-deprecated-1.c, gcc.dg/c2x-attr-deprecated-2.c,
	gcc.dg/c2x-attr-deprecated-3.c: New tests.

From-SVN: r278268

3 files changed, 7 insertions, 3 deletions

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index f4fdccc..571cf2b 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,8 @@
+2019-11-15  Joseph Myers  <joseph@codesourcery.com>
+
+	* c-attribs.c (handle_deprecated_attribute): Remove static.
+	* c-common.h (handle_deprecated_attribute): Declare.
+
 2019-11-14  Joseph Myers  <joseph@codesourcery.com>
 
 	* c-lex.c (lex_charconst): Make CPP_UTF8CHAR constants unsigned
diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index c62cebf..18b829f 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -115,8 +115,6 @@ static tree handle_pure_attribute (tree *, tree, tree, int, bool *);
 static tree handle_tm_attribute (tree *, tree, tree, int, bool *);
 static tree handle_tm_wrap_attribute (tree *, tree, tree, int, bool *);
 static tree handle_novops_attribute (tree *, tree, tree, int, bool *);
-static tree handle_deprecated_attribute (tree *, tree, tree, int,
-					 bool *);
 static tree handle_vector_size_attribute (tree *, tree, tree, int,
 					  bool *);
 static tree handle_nonnull_attribute (tree *, tree, tree, int, bool *);
@@ -3468,7 +3466,7 @@ handle_novops_attribute (tree *node, tree ARG_UNUSED (name),
 /* Handle a "deprecated" attribute; arguments as in
    struct attribute_spec.handler.  */
 
-static tree
+tree
 handle_deprecated_attribute (tree *node, tree name,
 			     tree args, int flags,
 			     bool *no_add_attrs)
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 80a8c9f..ad40c15 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1357,6 +1357,7 @@ extern void warn_for_multistatement_macros (location_t, location_t,
 
 /* In c-attribs.c.  */
 extern bool attribute_takes_identifier_p (const_tree);
+extern tree handle_deprecated_attribute (tree *, tree, tree, int, bool *);
 extern tree handle_unused_attribute (tree *, tree, tree, int, bool *);
 extern int parse_tm_stmt_attr (tree, int);
 extern int tm_attr_to_mask (tree);