preprocessor: Support #warning for standard C2x

ISO C2x standardizes the existing #warning extension.  Arrange
accordingly for it not to be diagnosed with -std=c2x -pedantic, but to
be diagnosed with -Wc11-c2x-compat.

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

gcc/testsuite/
	* gcc.dg/cpp/c11-warning-1.c, gcc.dg/cpp/c11-warning-2.c,
	gcc.dg/cpp/c11-warning-3.c, gcc.dg/cpp/c11-warning-4.c,
	gcc.dg/cpp/c2x-warning-1.c, gcc.dg/cpp/c2x-warning-2.c,
	gcc.dg/cpp/gnu11-warning-1.c, gcc.dg/cpp/gnu11-warning-2.c,
	gcc.dg/cpp/gnu11-warning-3.c, gcc.dg/cpp/gnu11-warning-4.c,
	gcc.dg/cpp/gnu2x-warning-1.c, gcc.dg/cpp/gnu2x-warning-2.c: New
	tests.

libcpp/
	* include/cpplib.h (struct cpp_options): Add warning_directive.
	* init.cc (struct lang_flags, lang_defaults): Add
	warning_directive.
	* directives.cc (DIRECTIVE_TABLE): Mark #warning as STDC2X not
	EXTENSION.
	(directive_diagnostics): Diagnose #warning with -Wc11-c2x-compat,
	or with -pedantic for a standard not supporting #warning.

3 files changed, 40 insertions, 26 deletions

diff --git a/libcpp/directives.cc b/libcpp/directives.cc
index 4104d51..802bd8c 100644
--- a/libcpp/directives.cc
+++ b/libcpp/directives.cc
@@ -158,7 +158,7 @@ static void cpp_pop_definition (cpp_reader *, struct def_pragma_macro *);
   D(elifndef,	T_ELIFNDEF,	STDC2X,    COND | ELIFDEF)		\
   D(error,	T_ERROR,	STDC89,    0)				\
   D(pragma,	T_PRAGMA,	STDC89,    IN_I)			\
-  D(warning,	T_WARNING,	EXTENSION, 0)				\
+  D(warning,	T_WARNING,	STDC2X,    0)				\
   D(include_next, T_INCLUDE_NEXT, EXTENSION, INCL | EXPAND)		\
   D(ident,	T_IDENT,	EXTENSION, IN_I)			\
   D(import,	T_IMPORT,	EXTENSION, INCL | EXPAND)  /* ObjC */	\
@@ -385,6 +385,15 @@ directive_diagnostics (cpp_reader *pfile, const directive *dir, int indented)
 	  && !(dir == &dtable[T_IMPORT] && CPP_OPTION (pfile, objc))
 	  && CPP_PEDANTIC (pfile))
 	cpp_error (pfile, CPP_DL_PEDWARN, "#%s is a GCC extension", dir->name);
+      else if (dir == &dtable[T_WARNING])
+	{
+	  if (CPP_PEDANTIC (pfile) && !CPP_OPTION (pfile, warning_directive))
+	    cpp_error (pfile, CPP_DL_PEDWARN,
+		       "#%s before C2X is a GCC extension", dir->name);
+	  else if (CPP_OPTION (pfile, cpp_warn_c11_c2x_compat) > 0)
+	    cpp_warning (pfile, CPP_W_C11_C2X_COMPAT,
+			 "#%s before C2X is a GCC extension", dir->name);
+	}
       else if (((dir->flags & DEPRECATED) != 0
 		|| (dir == &dtable[T_IMPORT] && !CPP_OPTION (pfile, objc)))
 	       && CPP_OPTION (pfile, cpp_warn_deprecated))
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index 26e2b4c..58ed51d 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -513,6 +513,9 @@ struct cpp_options
   /* Nonzero for the '#elifdef' and '#elifndef' directives.  */
   unsigned char elifdef;
 
+  /* Nonzero for the '#warning' directive.  */
+  unsigned char warning_directive;
+
   /* Nonzero means tokenize C++20 module directives.  */
   unsigned char module_directives;
 
diff --git a/libcpp/init.cc b/libcpp/init.cc
index 59641a7..8d99bdb 100644
--- a/libcpp/init.cc
+++ b/libcpp/init.cc
@@ -96,34 +96,35 @@ struct lang_flags
   char dfp_constants;
   char size_t_literals;
   char elifdef;
+  char warning_directive;
 };
 
 static const struct lang_flags lang_defaults[] =
-{ /*              c99 c++ xnum xid c11 std digr ulit rlit udlit bincst digsep trig u8chlit vaopt scope dfp szlit elifdef */
-  /* GNUC89   */  { 0,  0,  1,  0,  0,  0,  1,   0,   0,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0 },
-  /* GNUC99   */  { 1,  0,  1,  1,  0,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0 },
-  /* GNUC11   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0 },
-  /* GNUC17   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0 },
-  /* GNUC2X   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    1,     1,     0,   1,      1,   1,     1,   0,   1 },
-  /* STDC89   */  { 0,  0,  0,  0,  0,  1,  0,   0,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0 },
-  /* STDC94   */  { 0,  0,  0,  0,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0 },
-  /* STDC99   */  { 1,  0,  1,  1,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0 },
-  /* STDC11   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0 },
-  /* STDC17   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0 },
-  /* STDC2X   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    1,     1,     1,   1,      0,   1,     1,   0,   1 },
-  /* GNUCXX   */  { 0,  1,  1,  1,  0,  0,  1,   0,   0,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0 },
-  /* CXX98    */  { 0,  1,  0,  1,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   1,     0,   0,   0 },
-  /* GNUCXX11 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    0,     0,     0,   0,      1,   1,     0,   0,   0 },
-  /* CXX11    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    0,     0,     1,   0,      0,   1,     0,   0,   0 },
-  /* GNUCXX14 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   0,      1,   1,     0,   0,   0 },
-  /* CXX14    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    1,     1,     1,   0,      0,   1,     0,   0,   0 },
-  /* GNUCXX17 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   0,   0 },
-  /* CXX17    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      0,   1,     0,   0,   0 },
-  /* GNUCXX20 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   0,   0 },
-  /* CXX20    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   0,   0 },
-  /* GNUCXX23 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   1,   1 },
-  /* CXX23    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   1,   1 },
-  /* ASM      */  { 0,  0,  1,  0,  0,  0,  0,   0,   0,   0,    0,     0,     0,   0,      0,   0,     0,   0,   0 }
+{ /*              c99 c++ xnum xid c11 std digr ulit rlit udlit bincst digsep trig u8chlit vaopt scope dfp szlit elifdef warndir */
+  /* GNUC89   */  { 0,  0,  1,  0,  0,  0,  1,   0,   0,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0,      0 },
+  /* GNUC99   */  { 1,  0,  1,  1,  0,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0,      0 },
+  /* GNUC11   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0,      0 },
+  /* GNUC17   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0,      0 },
+  /* GNUC2X   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    1,     1,     0,   1,      1,   1,     1,   0,   1,      1 },
+  /* STDC89   */  { 0,  0,  0,  0,  0,  1,  0,   0,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0,      0 },
+  /* STDC94   */  { 0,  0,  0,  0,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0,      0 },
+  /* STDC99   */  { 1,  0,  1,  1,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0,      0 },
+  /* STDC11   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0,      0 },
+  /* STDC17   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0,   0,     0,   0,   0,      0 },
+  /* STDC2X   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    1,     1,     1,   1,      0,   1,     1,   0,   1,      1 },
+  /* GNUCXX   */  { 0,  1,  1,  1,  0,  0,  1,   0,   0,   0,    0,     0,     0,   0,      1,   1,     0,   0,   0,      0 },
+  /* CXX98    */  { 0,  1,  0,  1,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   1,     0,   0,   0,      0 },
+  /* GNUCXX11 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    0,     0,     0,   0,      1,   1,     0,   0,   0,      0 },
+  /* CXX11    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    0,     0,     1,   0,      0,   1,     0,   0,   0,      0 },
+  /* GNUCXX14 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   0,      1,   1,     0,   0,   0,      0 },
+  /* CXX14    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    1,     1,     1,   0,      0,   1,     0,   0,   0,      0 },
+  /* GNUCXX17 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   0,   0,      0 },
+  /* CXX17    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      0,   1,     0,   0,   0,      0 },
+  /* GNUCXX20 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   0,   0,      0 },
+  /* CXX20    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   0,   0,      0 },
+  /* GNUCXX23 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   1,   1,      0 },
+  /* CXX23    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1,     0,   1,   1,      0 },
+  /* ASM      */  { 0,  0,  1,  0,  0,  0,  0,   0,   0,   0,    0,     0,     0,   0,      0,   0,     0,   0,   0,      0 }
 };
 
 /* Sets internal flags correctly for a given language.  */
@@ -153,6 +154,7 @@ cpp_set_lang (cpp_reader *pfile, enum c_lang lang)
   CPP_OPTION (pfile, dfp_constants)		 = l->dfp_constants;
   CPP_OPTION (pfile, size_t_literals)		 = l->size_t_literals;
   CPP_OPTION (pfile, elifdef)			 = l->elifdef;
+  CPP_OPTION (pfile, warning_directive)		 = l->warning_directive;
 }
 
 /* Initialize library global state.  */