regex: Silence -Wzero-as-null-pointer-constant warning.

[Collin Funk]

I pushed the attached patch to silence this warning:

    $ gnulib-tool --create-testdir --dir testdir1 regex
    $ cd testdir1
    $ ./configure CFLAGS='-Wzero-as-null-pointer-constant'
    $ make
    [...]
    gcc -DHAVE_CONFIG_H -I. -I..  -DGNULIB_STRICT_CHECKING=1   
-Wzero-as-null-pointer-constant -MT regex.o -MD -MP -MF $depbase.Tpo -c -o 
regex.o regex.c &&\
    mv -f $depbase.Tpo $depbase.Po
    In file included from regex.c:72:
    regexec.c: In function ‘merge_state_with_log’:
    regexec.c:2344:40: warning: zero as null pointer constant 
[-Wzero-as-null-pointer-constant]
     2344 |   else if (mctx->state_log[cur_idx] == 0)
          |
    [...]

The 'git blame' shows the code is many years old. I just only noticed it
now since we began replacing glibc's regex.

Collin


>From b6e096af3876e0e4093c0c885abe311a7cb9c3e5 Mon Sep 17 00:00:00 2001
Message-ID: <b6e096af3876e0e4093c0c885abe311a7cb9c3e5.1776401903.git.collin.fu...@gmail.com>
From: Collin Funk <collin.fu...@gmail.com>
Date: Thu, 16 Apr 2026 21:50:27 -0700
Subject: [PATCH] regex: Silence -Wzero-as-null-pointer-constant warning.

* lib/regexec.c (merge_state_with_log): Check the pointer against NULL.
---
 ChangeLog     | 5 +++++
 lib/regexec.c | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 59b4906765..39529954bc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2026-04-16  Collin Funk  <collin.fu...@gmail.com>
+
+	regex: Silence -Wzero-as-null-pointer-constant warning.
+	* lib/regexec.c (merge_state_with_log): Check the pointer against NULL.
+
 2026-04-16  Bruno Haible  <br...@clisp.org>
 
 	byteswap: Fix compilation on Solaris OpenIndiana (regr. 2026-03-20).
diff --git a/lib/regexec.c b/lib/regexec.c
index 65d4d0f09e..ff62ac08ef 100644
--- a/lib/regexec.c
+++ b/lib/regexec.c
@@ -2341,7 +2341,7 @@ merge_state_with_log (reg_errcode_t *err, re_match_context_t *mctx,
       mctx->state_log[cur_idx] = next_state;
       mctx->state_log_top = cur_idx;
     }
-  else if (mctx->state_log[cur_idx] == 0)
+  else if (mctx->state_log[cur_idx] == NULL)
     {
       mctx->state_log[cur_idx] = next_state;
     }
-- 
2.53.0