preprocessor: C2x identifier rules

C2x has, like C++, adopted rules for identifiers based directly on an
unversioned normative reference to Unicode.  Make libcpp follow those
rules for c2x / gnu2x standards (this involves bringing back a flag
separate from the C++ one for whether to use these identifier rules,
but this time enabled for all C++ language versions since that was the
conclusion adopted for C++ identifier handling).

There is one change here that affects C++.  I believe the new
normative requirement for NFC only applies to identifiers, not to the
use of identifier-continue characters in pp-numbers, where there is no
such requirement and so the diagnostic ought to be a warning not a
pedwarn in pp-numbers, and that this is the case for both C and C++.

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

libcpp/
	* charset.cc (ucn_valid_in_identifier): Check xid_identifiers not
	cplusplus to determine whether to use CXX23 and NXX23 flags.
	* include/cpplib.h (struct cpp_options): Add xid_identifiers.
	* init.cc (struct lang_flags, lang_defaults): Add xid_identifiers.
	(cpp_set_lang): Set xid_identifiers.
	* lex.cc (warn_about_normalization): Add parameter identifier.
	Only pedwarn about non-NFC for identifiers, not pp-numbers.
	(_cpp_lex_direct): Update calls to warn_about_normalization.

gcc/testsuite/
	* gcc.dg/cpp/c2x-ucnid-1-utf8.c, gcc.dg/cpp/c2x-ucnid-1.c: New
	tests.

1 files changed, 7 insertions, 6 deletions

diff --git a/libcpp/lex.cc b/libcpp/lex.cc
index a429a3d..cc12a52d 100644
--- a/libcpp/lex.cc
+++ b/libcpp/lex.cc
@@ -2007,7 +2007,8 @@ name_p (cpp_reader *pfile, const cpp_string *string)
 static void
 warn_about_normalization (cpp_reader *pfile, 
 			  const cpp_token *token,
-			  const struct normalize_state *s)
+			  const struct normalize_state *s,
+			  bool identifier)
 {
   if (CPP_OPTION (pfile, warn_normalize) < NORMALIZE_STATE_RESULT (s)
       && !pfile->state.skipping)
@@ -2043,7 +2044,7 @@ warn_about_normalization (cpp_reader *pfile,
       if (NORMALIZE_STATE_RESULT (s) == normalized_C)
 	cpp_warning_at (pfile, CPP_W_NORMALIZE, &rich_loc,
 			"`%.*s' is not in NFKC", (int) sz, buf);
-      else if (CPP_OPTION (pfile, cplusplus))
+      else if (identifier && CPP_OPTION (pfile, xid_identifiers))
 	cpp_pedwarning_at (pfile, CPP_W_NORMALIZE, &rich_loc,
 				  "`%.*s' is not in NFC", (int) sz, buf);
       else
@@ -3839,7 +3840,7 @@ _cpp_lex_direct (cpp_reader *pfile)
 	struct normalize_state nst = INITIAL_NORMALIZE_STATE;
 	result->type = CPP_NUMBER;
 	lex_number (pfile, &result->val.str, &nst);
-	warn_about_normalization (pfile, result, &nst);
+	warn_about_normalization (pfile, result, &nst, false);
 	break;
       }
 
@@ -3888,7 +3889,7 @@ _cpp_lex_direct (cpp_reader *pfile)
 	result->val.node.node = lex_identifier (pfile, buffer->cur - 1, false,
 						&nst,
 						&result->val.node.spelling);
-	warn_about_normalization (pfile, result, &nst);
+	warn_about_normalization (pfile, result, &nst, true);
       }
 
       /* Convert named operators to their proper types.  */
@@ -4101,7 +4102,7 @@ _cpp_lex_direct (cpp_reader *pfile)
 	  struct normalize_state nst = INITIAL_NORMALIZE_STATE;
 	  result->type = CPP_NUMBER;
 	  lex_number (pfile, &result->val.str, &nst);
-	  warn_about_normalization (pfile, result, &nst);
+	  warn_about_normalization (pfile, result, &nst, false);
 	}
       else if (*buffer->cur == '.' && buffer->cur[1] == '.')
 	buffer->cur += 2, result->type = CPP_ELLIPSIS;
@@ -4192,7 +4193,7 @@ _cpp_lex_direct (cpp_reader *pfile)
 	    result->type = CPP_NAME;
 	    result->val.node.node = lex_identifier (pfile, base, true, &nst,
 						    &result->val.node.spelling);
-	    warn_about_normalization (pfile, result, &nst);
+	    warn_about_normalization (pfile, result, &nst, true);
 	    break;
 	  }