Thanks; I installed the attached somewhat fancier patch into Gnulib.
From efd5c380ff8062541d5fd98b050ecd3cb295917c Mon Sep 17 00:00:00 2001
From: Paul Eggert <egg...@cs.ucla.edu>
Date: Sun, 13 Apr 2025 18:01:08 -0700
Subject: [PATCH] regex: match current Emacs behavior
* config/srclist.txt: Comment out regex.h, since we now
disagree with glibc.
* lib/regex.h (RE_SYNTAX_EMACS):
Match Emacs 21+ behavior, not Emacs 20-.
* m4/regex.m4 (gl_REGEX): Check for this Emacs fix.
---
ChangeLog | 9 +++++++++
config/srclist.txt | 2 +-
doc/regex.texi | 3 ++-
lib/regex.h | 8 ++++----
m4/regex.m4 | 6 +++++-
5 files changed, 21 insertions(+), 7 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 2ea548d13f..c20c151757 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2025-04-13 Paul Eggert <egg...@cs.ucla.edu>
+
+ regex: match current Emacs behavior
+ * config/srclist.txt: Comment out regex.h, since we now
+ disagree with glibc.
+ * lib/regex.h (RE_SYNTAX_EMACS):
+ Match Emacs 21+ behavior, not Emacs 20-.
+ * m4/regex.m4 (gl_REGEX): Check for this Emacs fix.
+
2025-04-13 Bruno Haible <br...@clisp.org>
getlogin_r tests: Avoid writing to a literal string.
diff --git a/config/srclist.txt b/config/srclist.txt
index 173f23edaf..62816dcf4a 100644
--- a/config/srclist.txt
+++ b/config/srclist.txt
@@ -68,7 +68,7 @@ $LIBCSRC malloc/scratch_buffer_set_array_size.c lib/malloc
#$LIBCSRC misc/sys/cdefs.h lib
#$LIBCSRC posix/regcomp.c lib
$LIBCSRC posix/regex.c lib
-$LIBCSRC posix/regex.h lib
+#$LIBCSRC posix/regex.h lib
#$LIBCSRC posix/regex_internal.c lib
#$LIBCSRC posix/regex_internal.h lib
#$LIBCSRC posix/regexec.c lib
diff --git a/doc/regex.texi b/doc/regex.texi
index cba1e13520..925b0db639 100644
--- a/doc/regex.texi
+++ b/doc/regex.texi
@@ -316,7 +316,8 @@ regular expressions.
The predefined syntaxes---taken directly from @file{regex.h}---are:
@smallexample
-#define RE_SYNTAX_EMACS 0
+# define RE_SYNTAX_EMACS \
+ (RE_CHAR_CLASSES | RE_INTERVALS)
#define RE_SYNTAX_AWK \
(RE_BACKSLASH_ESCAPE_IN_LISTS | RE_DOT_NOT_NULL \
diff --git a/lib/regex.h b/lib/regex.h
index 67a3aa70a5..c4c6089a8c 100644
--- a/lib/regex.h
+++ b/lib/regex.h
@@ -66,9 +66,8 @@ typedef unsigned long int active_reg_t;
/* The following bits are used to determine the regexp syntax we
recognize. The set/not-set meanings are chosen so that Emacs syntax
- remains the value 0. The bits are given in alphabetical order, and
- the definitions shifted by one from the previous bit; thus, when we
- add or remove a bit, only one other definition need change. */
+ is the value 0 for Emacs 20 (2000) and earlier, and the value
+ RE_SYNTAX_EMACS for Emacs 21 (2001) and later. */
typedef unsigned long int reg_syntax_t;
#ifdef __USE_GNU
@@ -215,7 +214,8 @@ extern reg_syntax_t re_syntax_options;
(The [[[ comments delimit what gets put into the Texinfo file, so
don't delete them!) */
/* [[[begin syntaxes]]] */
-# define RE_SYNTAX_EMACS 0
+# define RE_SYNTAX_EMACS \
+ (RE_CHAR_CLASSES | RE_INTERVALS)
# define RE_SYNTAX_AWK \
(RE_BACKSLASH_ESCAPE_IN_LISTS | RE_DOT_NOT_NULL \
diff --git a/m4/regex.m4 b/m4/regex.m4
index 80dfb8e1e5..1b2012fe00 100644
--- a/m4/regex.m4
+++ b/m4/regex.m4
@@ -1,5 +1,5 @@
# regex.m4
-# serial 78
+# serial 79
dnl Copyright (C) 1996-2001, 2003-2025 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -53,6 +53,10 @@ AC_DEFUN([gl_REGEX],
/* Exit with distinguishable exit code. */
static void sigabrt_no_core (int sig) { raise (SIGTERM); }
#endif
+
+ #if RE_SYNTAX_EMACS != (RE_CHAR_CLASSES | RE_INTERVALS)
+ # error "RE_SYNTAX_EMACS does not match Emacs behavior"
+ #endif
]],
[[int result = 0;
static struct re_pattern_buffer regex;
--
2.45.2
