Add -std=c2x, -std=gnu2x, -Wc11-c2x-compat, C2X _Static_assert support.

Now new features are starting to be added to a C2X draft (in the C2x
branch of the C standard git repository, no public WG14 document yet),
it's time to add -std=c2x and associated options to GCC for use in
enabling C2X features.

This patch adds the expected set of options: -std=c2x, -std=gnu2x,
-Wc11-c2x-compat.  A first C2X feature is added (the only one so far
in the repository that's obviously relevant to GCC): support (as in
C++) for the string constant to be omitted in _Static_assert.  This
feature is duly also supported as an extension in earlier standard
modes (diagnosed with -pedantic, unless -Wno-c11-c2x-compat is given,
or with -Wc11-c2x-compat even in C2X mode).

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

gcc/
	* doc/cpp.texi (__STDC_VERSION__): Document C2X handling.
	* doc/invoke.texi (-std=c2x, -std=gnu2x): Document new options.
	* doc/standards.texi (C Language): Document C2X.
	* dwarf2out.c (highest_c_language), config/rl78/rl78.c
	(rl78_option_override): Handle "GNU C2X" language name.

gcc/c/
	* c-errors.c (pedwarn_c11): New function.
	* c-parser.c (disable_extension_diagnostics): Save
	warn_c11_c2x_compat and set it to 0.
	(restore_extension_diagnostics): Restore warn_c11_c2x_compat.
	(c_parser_static_assert_declaration_no_semi): Handle
	_Static_assert without string constant.
	* c-tree.h (pedwarn_c11): New prototype.

gcc/c-family/
	* c-common.c (flag_isoc2x): New variable.
	* c-common.h (clk_c): Update comment to reference C2X.
	(flag_isoc99, flag_isoc11): Update comments to reference future
	standard versions in general.
	(flag_isoc2x): Declare.
	* c-opts.c (set_std_c2x): New function.
	(c_common_handle_option): Handle -std=c2x and -std=gnu2x.
	(set_std_c89, set_std_c99, set_std_c11, set_std_c17): Set
	flag_isoc2x to 0.
	* c.opt (Wc11-c2x-compat, std=c2x, std=gnu2x): New options.

gcc/testsuite/
	* gcc.dg/c11-static-assert-7.c, gcc.dg/c11-static-assert-8.c,
	gcc.dg/c11-static-assert-9.c, gcc.dg/c2x-static-assert-1.c,
	gcc.dg/c2x-static-assert-2.c, gcc.dg/c99-static-assert-2.c,
	gcc.dg/gnu2x-static-assert-1.c: New tests.
	* gcc.dg/missing-symbol-3.c: Update expected fix-it text.

libcpp/
	* include/cpplib.h (enum c_lang): Add CLK_GNUC2X and CLK_STDC2X.
	* init.c (lang_defaults): Add GNUC2X and STDC2X entries.
	(cpp_init_builtins): Define __STDC_VERSION__ to 202000L for C2X.

From-SVN: r265251

4 files changed, 91 insertions, 20 deletions

diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 4807a32..2c07f2f 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,13 @@
+2018-10-17  Joseph Myers  <joseph@codesourcery.com>
+
+	* c-errors.c (pedwarn_c11): New function.
+	* c-parser.c (disable_extension_diagnostics): Save
+	warn_c11_c2x_compat and set it to 0.
+	(restore_extension_diagnostics): Restore warn_c11_c2x_compat.
+	(c_parser_static_assert_declaration_no_semi): Handle
+	_Static_assert without string constant.
+	* c-tree.h (pedwarn_c11): New prototype.
+
 2018-10-17  David Malcolm  <dmalcolm@redhat.com>
 
 	* Make-lang.in (selftest-c): New.
diff --git a/gcc/c/c-errors.c b/gcc/c/c-errors.c
index 2d50710..4ff2080 100644
--- a/gcc/c/c-errors.c
+++ b/gcc/c/c-errors.c
@@ -25,6 +25,45 @@ along with GCC; see the file COPYING3.  If not see
 #include "c-tree.h"
 #include "opts.h"
 
+/* Issue an ISO C11 pedantic warning MSGID if -pedantic outside C2X mode,
+   otherwise issue warning MSGID if -Wc11-c2X-compat is specified.
+   This function is supposed to be used for matters that are allowed in
+   ISO C2X but not supported in ISO C11, thus we explicitly don't pedwarn
+   when C2X is specified.  */
+
+bool
+pedwarn_c11 (location_t location, int opt, const char *gmsgid, ...)
+{
+  diagnostic_info diagnostic;
+  va_list ap;
+  bool warned = false;
+  rich_location richloc (line_table, location);
+
+  va_start (ap, gmsgid);
+  /* If desired, issue the C11/C2X compat warning, which is more specific
+     than -pedantic.  */
+  if (warn_c11_c2x_compat > 0)
+    {
+      diagnostic_set_info (&diagnostic, gmsgid, &ap, &richloc,
+			   (pedantic && !flag_isoc2x)
+			   ? DK_PEDWARN : DK_WARNING);
+      diagnostic.option_index = OPT_Wc11_c2x_compat;
+      warned = diagnostic_report_diagnostic (global_dc, &diagnostic);
+    }
+  /* -Wno-c11-c2x-compat suppresses even the pedwarns.  */
+  else if (warn_c11_c2x_compat == 0)
+    ;
+  /* For -pedantic outside C2X, issue a pedwarn.  */
+  else if (pedantic && !flag_isoc2x)
+    {
+      diagnostic_set_info (&diagnostic, gmsgid, &ap, &richloc, DK_PEDWARN);
+      diagnostic.option_index = opt;
+      warned = diagnostic_report_diagnostic (global_dc, &diagnostic);
+    }
+  va_end (ap);
+  return warned;
+}
+
 /* Issue an ISO C99 pedantic warning MSGID if -pedantic outside C11 mode,
    otherwise issue warning MSGID if -Wc99-c11-compat is specified.
    This function is supposed to be used for matters that are allowed in
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 1f173fc..ee66ce8 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -1327,6 +1327,9 @@ disable_extension_diagnostics (void)
 	     /* Similarly for warn_c99_c11_compat.  */
 	     | ((warn_c99_c11_compat == 1) << 9)
 	     | ((warn_c99_c11_compat == -1) << 10)
+	     /* Similarly for warn_c11_c2x_compat.  */
+	     | ((warn_c11_c2x_compat == 1) << 11)
+	     | ((warn_c11_c2x_compat == -1) << 12)
 	     );
   cpp_opts->cpp_pedantic = pedantic = 0;
   warn_pointer_arith = 0;
@@ -1337,6 +1340,7 @@ disable_extension_diagnostics (void)
   warn_overlength_strings = 0;
   warn_c90_c99_compat = 0;
   warn_c99_c11_compat = 0;
+  warn_c11_c2x_compat = 0;
   return ret;
 }
 
@@ -1356,6 +1360,7 @@ restore_extension_diagnostics (int flags)
   /* See above for why is this needed.  */
   warn_c90_c99_compat = (flags >> 7) & 1 ? 1 : ((flags >> 8) & 1 ? -1 : 0);
   warn_c99_c11_compat = (flags >> 9) & 1 ? 1 : ((flags >> 10) & 1 ? -1 : 0);
+  warn_c11_c2x_compat = (flags >> 11) & 1 ? 1 : ((flags >> 12) & 1 ? -1 : 0);
 }
 
 /* Helper data structure for parsing #pragma acc routine.  */
@@ -2404,6 +2409,10 @@ c_parser_static_assert_declaration (c_parser *parser)
 
    static_assert-declaration-no-semi:
      _Static_assert ( constant-expression , string-literal )
+
+   C2X:
+   static_assert-declaration-no-semi:
+     _Static_assert ( constant-expression )
 */
 
 static void
@@ -2411,7 +2420,7 @@ c_parser_static_assert_declaration_no_semi (c_parser *parser)
 {
   location_t assert_loc, value_loc;
   tree value;
-  tree string;
+  tree string = NULL_TREE;
 
   gcc_assert (c_parser_next_token_is_keyword (parser, RID_STATIC_ASSERT));
   assert_loc = c_parser_peek_token (parser)->location;
@@ -2429,27 +2438,33 @@ c_parser_static_assert_declaration_no_semi (c_parser *parser)
   value = c_parser_expr_no_commas (parser, NULL).value;
   value_loc = EXPR_LOC_OR_LOC (value, value_tok_loc);
   parser->lex_untranslated_string = true;
-  if (!c_parser_require (parser, CPP_COMMA, "expected %<,%>"))
-    {
-      parser->lex_untranslated_string = false;
-      return;
-    }
-  switch (c_parser_peek_token (parser)->type)
+  if (c_parser_next_token_is (parser, CPP_COMMA))
     {
-    case CPP_STRING:
-    case CPP_STRING16:
-    case CPP_STRING32:
-    case CPP_WSTRING:
-    case CPP_UTF8STRING:
-      string = c_parser_peek_token (parser)->value;
       c_parser_consume_token (parser);
-      parser->lex_untranslated_string = false;
-      break;
-    default:
-      c_parser_error (parser, "expected string literal");
-      parser->lex_untranslated_string = false;
-      return;
+      switch (c_parser_peek_token (parser)->type)
+	{
+	case CPP_STRING:
+	case CPP_STRING16:
+	case CPP_STRING32:
+	case CPP_WSTRING:
+	case CPP_UTF8STRING:
+	  string = c_parser_peek_token (parser)->value;
+	  c_parser_consume_token (parser);
+	  parser->lex_untranslated_string = false;
+	  break;
+	default:
+	  c_parser_error (parser, "expected string literal");
+	  parser->lex_untranslated_string = false;
+	  return;
+	}
     }
+  else if (flag_isoc11)
+    /* If pedantic for pre-C11, the use of _Static_assert itself will
+       have been diagnosed, so do not also diagnose the use of this
+       new C2X feature of _Static_assert.  */
+    pedwarn_c11 (assert_loc, OPT_Wpedantic,
+		 "ISO C11 does not support omitting the string in "
+		 "%<_Static_assert%>");
   parens.require_close (parser);
 
   if (!INTEGRAL_TYPE_P (TREE_TYPE (value)))
@@ -2473,7 +2488,12 @@ c_parser_static_assert_declaration_no_semi (c_parser *parser)
     }
   constant_expression_warning (value);
   if (integer_zerop (value))
-    error_at (assert_loc, "static assertion failed: %E", string);
+    {
+      if (string)
+	error_at (assert_loc, "static assertion failed: %E", string);
+      else
+	error_at (assert_loc, "static assertion failed");
+    }
 }
 
 /* Parse some declaration specifiers (possibly none) (C90 6.5, C99
diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
index 017c01c..be63fee 100644
--- a/gcc/c/c-tree.h
+++ b/gcc/c/c-tree.h
@@ -762,6 +762,8 @@ extern bool pedwarn_c90 (location_t, int opt, const char *, ...)
     ATTRIBUTE_GCC_DIAG(3,4);
 extern bool pedwarn_c99 (location_t, int opt, const char *, ...)
     ATTRIBUTE_GCC_DIAG(3,4);
+extern bool pedwarn_c11 (location_t, int opt, const char *, ...)
+    ATTRIBUTE_GCC_DIAG(3,4);
 
 extern void
 set_c_expr_source_range (c_expr *expr,