getgroups, getugroups: provide stubs for mingw

Avoid link failure on mingw, which lacks getgroups and anything
else related to gid_t management (stat.st_gid is always 0).

* lib/getgroups.c (getgroups): Provide ENOSYS stub for mingw.
* lib/getugroups.c (getugroups): Likewise.
* m4/getgroups.m4 (gl_FUNC_GETGROUPS): Check for missing
function.  Modernize replacement scheme.
(gl_PREREQ_GETGROUPS): Delete.
* m4/getugroups.m4 (gl_GETUGROUPS): Check for <grp.h>.
* modules/getgroups (configure.ac): Declare witness.
* m4/unistd_h.m4 (gl_UNISTD_H_DEFAULTS): Add default.
* modules/unistd (Depends-on): Substitute witness.
* lib/unistd.in.h (getgroups): Declare replacement.

Signed-off-by: Eric Blake <ebb9@byu.net>

3 files changed, 58 insertions, 10 deletions

diff --git a/lib/getgroups.c b/lib/getgroups.c
index e764d732fc..bad676ea5e 100644
--- a/lib/getgroups.c
+++ b/lib/getgroups.c
@@ -25,7 +25,20 @@
 #include <errno.h>
 #include <stdlib.h>
 
-#undef getgroups
+#if !HAVE_GETGROUPS
+
+/* Provide a stub that fails with ENOSYS, since there is no group
+   information available on mingw.  */
+int
+getgroups (int n _UNUSED_PARAMETER_, GETGROUPS_T *groups _UNUSED_PARAMETER_)
+{
+  errno = ENOSYS;
+  return -1;
+}
+
+#else /* HAVE_GETGROUPS */
+
+# undef getgroups
 
 /* On at least Ultrix 4.3 and NextStep 3.2, getgroups (0, NULL) always
    fails.  On other systems, it returns the number of supplemental
@@ -66,3 +79,5 @@ rpl_getgroups (int n, GETGROUPS_T *group)
 
   return n_groups;
 }
+
+#endif /* HAVE_GETGROUPS */
diff --git a/lib/getugroups.c b/lib/getugroups.c
index 2207b85a17..a614ec7be3 100644
--- a/lib/getugroups.c
+++ b/lib/getugroups.c
@@ -21,22 +21,31 @@
 
 #include "getugroups.h"
 
+#include <errno.h>
 #include <limits.h>
 #include <stdio.h> /* grp.h on alpha OSF1 V2.0 uses "FILE *". */
-#include <grp.h>
-
+#include <string.h>
 #include <unistd.h>
 
-#include <errno.h>
+#if !HAVE_GRP_H
 
-/* Some old header files might not declare setgrent, getgrent, and endgrent.
-   If you don't have them at all, we can't implement this function.
-   You lose!  */
-struct group *getgrent (void);
+/* Mingw lacks all things related to group management.  The best we
+   can do is fail with ENOSYS.  */
 
-#include <string.h>
+int
+getugroups (int maxcount _UNUSED_PARAMETER_,
+            gid_t *grouplist _UNUSED_PARAMETER_,
+            char const *username _UNUSED_PARAMETER_,
+            gid_t gid _UNUSED_PARAMETER_)
+{
+  errno = ENOSYS;
+  return -1;
+}
 
-#define STREQ(s1, s2) (strcmp (s1, s2) == 0)
+#else /* HAVE_GRP_H */
+# include <grp.h>
+
+# define STREQ(s1, s2) (strcmp (s1, s2) == 0)
 
 /* Like `getgroups', but for user USERNAME instead of for the current
    process.  Store at most MAXCOUNT group IDs in the GROUPLIST array.
@@ -112,3 +121,5 @@ getugroups (int maxcount, GETGROUPS_T *grouplist, char const *username,
 
   return count;
 }
+
+#endif /* HAVE_GRP_H */
diff --git a/lib/unistd.in.h b/lib/unistd.in.h
index b6d2fa06b8..90494e4d1d 100644
--- a/lib/unistd.in.h
+++ b/lib/unistd.in.h
@@ -406,6 +406,28 @@ extern int getdtablesize (void);
 #endif
 
 
+#if @GNULIB_GETGROUPS@
+# if @REPLACE_GETGROUPS@
+#  undef getgroups
+#  define getgroups rpl_getgroups
+# endif
+# if !@HAVE_GETGROUPS@ || @REPLACE_GETGROUPS@
+/* Return the supplemental groups that the current process belongs to.
+   It is unspecified whether the effective group id is in the list.
+   If N is 0, return the group count; otherwise, N describes how many
+   entries are available in GROUPS.  Return -1 and set errno if N is
+   not 0 and not large enough.  Fails with ENOSYS on some systems.  */
+int getgroups (int n, GETGROUPS_T *groups);
+# endif
+#elif defined GNULIB_POSIXCHECK
+# undef getgroups
+# define getgroups(n,g)                                                 \
+    (GL_LINK_WARNING ("getgroups is unportable - "                      \
+                      "use gnulib module getgroups for portability"),   \
+     getgroups (n, g))
+#endif
+
+
 #if @GNULIB_GETHOSTNAME@
 /* Return the standard host name of the machine.
    WARNING! The host name may or may not be fully qualified.