failed config.h substitution

[Bruno Haible]

Hi,

autoconf-2.52 doesn't substitute #undef's if they are followed by a comment
in the config.h.in. This is
   1. a regression versus autoconf-2.13.
   2. not documented in the manual.
Thus it looks like a bug.

To reproduce:

$ cat configure.in
AC_INIT(configure)
AC_CONFIG_HEADER(config.h)
AC_DEFINE(DIRENT)
AC_OUTPUT

$ cat config.h.in
#undef DIRENT   /* use <dirent.h> */

=============== WITH autoconf 2.13 ===============

$ autoconf --version
Autoconf version 2.13
$ autoconf
$ ./configure
loading cache ./config.cache
creating ./config.status
creating config.h
config.h is unchanged
$ cat config.h
/* config.h.  Generated automatically by configure.  */
#define DIRENT 1   /* use <dirent.h> */

=============== WITH autoconf 2.54b ===============

$ autoconf --version
autoconf (GNU Autoconf) 2.54b
Written by David J. MacKenzie and Akim Demaille.

Copyright 2002 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ autoconf
$ ./configure
configure: creating ./config.status
config.status: creating config.h
$ cat config.h
/* config.h.  Generated automatically by configure.  */
/* #undef DIRENT */   /* use <dirent.h> */