Overhaul AC_TYPE_GETGROUPS and AC_FUNC_GETGROUPS.

AC_TYPE_GETGROUPS is the last remaining use of AC_EGREP_HEADER in
stock Autoconf macros.  It uses it only when cross compiling, as a
fallback from an AC_RUN_IFELSE check, testing for a bug in system
headers from the late 1980s or early 1990s, where gid_t *existed*
but the second argument to getgroups needed to be an array of int,
and this didn’t cause a compile error (i.e. the system headers
declare getgroups with no prototype or an incorrect prototype).
AC_FUNC_GETGROUPS also uses AC_RUN_IFELSE to test for obscure
problems specific to long-obsolete Unixes.

The downsides of AC_RUN_IFELSE and AC_EGREP_HEADER seem more severe
than the chances of someone compiling a current-generation program,
that uses getgroups, on an OS old enough to have one of the really
nasty bugs.  Accordingly, this patch changes AC_FUNC_GETGROUPS to use
a host_os-based *blacklist* both in native and cross compilation.
This is limited to the two host_os values for which either our old
code, or Gnulib, documented a serious bug: ultrix* and nextstep*.
Currently it does not try to pin down the exact version ranges subject
to the bugs — that would require research by someone with access to
the full history of these OSes.

An incorrect guess by this blacklist can be overridden by setting
ac_cv_func_getgroups_works in config.site.  AC_TYPE_GETGROUPS, for its
part, now does a series of regular old AC_COMPILE_IFELSE checks to
probe the prototype of getgroups, and considers that good enough.

While I was in there I noticed that AC_FUNC_GETGROUPS does not
AC_SUBST a documented output variable, and that the name of this
variable is misspelled in the manual.

* lib/autoconf/functions.m4 (AC_FUNC_GETGROUPS): Use AC_SEARCH_LIBS
  to probe for getgroups.  Use an AC_CANONICAL_HOST-based blacklist
  for bug detection, not AC_RUN_IFELSE.  AC_SUBST the GETGROUPS_LIB
  output variable.
* lib/autoconf/types.m4 (AC_TYPE_GETGROUPS): Check only the prototype
  of getgroups, using AC_COMPILE_IFELSE; do not use either AC_RUN_IFELSE
  or AC_EGREP_HEADER.
* doc/autoconf.texi: Update to match. Correct misspelling of
  GETGROUPS_LIB.
* tests.local.at (_AT_CHECK_ENV): Allow GETGROUPS_LIB output variable.

1 files changed, 17 insertions, 8 deletions

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 037c8055..5d5f613e 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -5257,17 +5257,26 @@ and also contains workarounds for other portability problems of
 @defmac AC_FUNC_GETGROUPS
 @acindex{FUNC_GETGROUPS}
 @cvindex HAVE_GETGROUPS
-@ovindex GETGROUPS_LIBS
+@ovindex GETGROUPS_LIB
 @c @fuindex getgroups
 @prindex @code{getgroups}
 @caindex func_getgroups_works
-If the @code{getgroups} function is available and works,
-define @code{HAVE_GETGROUPS}.  Set @code{GETGROUPS_LIBS} to any libraries
-needed to get that function.  This macro runs @code{AC_TYPE_GETGROUPS}.
-
-This macro is obsolescent. New programs need not use this macro.  But
-they may want to use the Gnulib module @code{getgroups}, which provides
-workarounds to other portability problems of this function.
+Perform all the checks performed by @code{AC_TYPE_GETGROUPS}
+(@pxref{AC_TYPE_GETGROUPS}).
+Then, if the @code{getgroups} function is available
+and known to work correctly, define @code{HAVE_GETGROUPS}.
+Set the output variable @code{GETGROUPS_LIB} to any libraries
+needed to get that function.
+
+This macro relies on a list of systems with known, serious bugs in
+@code{getgroups}.  If this list mis-identifies your system's
+@code{getgroups} as buggy, or as not buggy, you can override it by
+setting the cache variable @code{ac_cv_func_getgroups_works} in a
+@file{config.site} file (@pxref{Site Defaults}).  Please also report the
+error to @email{bug-autoconf@@gnu.org, the Autoconf Bugs mailing list}.
+
+The Gnulib module @code{getgroups} provides workarounds for additional,
+less severe portability problems with this function.
 @end defmac
 
 @anchor{AC_FUNC_GETLOADAVG}