Re: [PATCH] c++, v2: Implement C++23 P2071R2 - Named universal character escapes [PR106648]

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Aug 31, 2022 at 05:07:29PM +0200, Jakub Jelinek via Gcc-patches wrote:
> Given what you said above, I think that is what we want for the last 2
> for C++23, the question is if it is ok also for C++20/C17 etc. and whether
> it should depend on -pedantic or -pedantic-errors or GNU vs. ISO mode
> or not in that case.  We could handle those 2 also differently, just
> warn instead of error for the \N{ABC} case if not in C++23 mode when
> identifier_pos.

Here is an incremental version of the patch which will make valid
\u{123} and \N{LATIN SMALL LETTER A WITH ACUTE} an extension in GNU
modes before C++23 and split it as separate tokens in ISO modes.

Testcase:
#define z(x) 0
#define a z(
int b = a\u{123});
int c = a\N{LATIN SMALL LETTER A WITH ACUTE});

--- libcpp/charset.cc.jj	2022-08-31 16:50:48.862775486 +0200
+++ libcpp/charset.cc	2022-08-31 17:18:59.649257350 +0200
@@ -1448,7 +1448,11 @@ _cpp_valid_ucn (cpp_reader *pfile, const
   if (str[-1] == 'u')
     {
       length = 4;
-      if (str < limit && *str == '{')
+      if (str < limit
+          && *str == '{'
+          && (!identifier_pos
+	      || CPP_OPTION (pfile, delimited_escape_seqs)
+	      || !CPP_OPTION (pfile, std)))
 	{
 	  str++;
 	  /* Magic value to indicate no digits seen.  */
@@ -1462,6 +1466,13 @@ _cpp_valid_ucn (cpp_reader *pfile, const
   else if (str[-1] == 'N')
     {
       length = 4;
+      if (identifier_pos
+	  && !CPP_OPTION (pfile, delimited_escape_seqs)
+	  && CPP_OPTION (pfile, std))
+	{
+	  *cp = 0;
+	  return false;
+	}
       if (str == limit || *str != '{')
 	{
 	  if (identifier_pos)

	Jakub