m4: handle id failures when checking ustar support

Fixes automake bug https://bugs.gnu.org/20713.

If `id` fails, display a specific warning message to the user.

* m4/tar.m4: Check $am_uid & $am_gid if they're unknown.

diff --git a/m4/tar.m4 b/m4/tar.m4
index 7e3df4f98e1c1690a1c3f511e6ae5a2d89763585..8f4d2f21394bd6f3f11c90c52630df911a5fe2a0 100644 (file)
--- a/m4/tar.m4
+++ b/m4/tar.m4
@@ -46,15 +46,19 @@ m4_if([$1], [v7],
       am_uid=`id -u || echo unknown`
       am_gid=`id -g || echo unknown`
       AC_MSG_CHECKING([whether UID '$am_uid' is supported by ustar format])
-      if test $am_uid -le $am_max_uid; then
-         AC_MSG_RESULT([yes])
+      if test x$am_uid = xunknown; then
+        AC_MSG_WARN([ancient id detected; assuming current UID is ok, but dist-ustar might not work])
+      elif test $am_uid -le $am_max_uid; then
+        AC_MSG_RESULT([yes])
       else
-         AC_MSG_RESULT([no])
-         _am_tools=none
+        AC_MSG_RESULT([no])
+        _am_tools=none
       fi
       AC_MSG_CHECKING([whether GID '$am_gid' is supported by ustar format])
-      if test $am_gid -le $am_max_gid; then
-         AC_MSG_RESULT([yes])
+      if test x$gm_gid = xunknown; then
+        AC_MSG_WARN([ancient id detected; assuming current GID is ok, but dist-ustar might not work])
+      elif test $am_gid -le $am_max_gid; then
+        AC_MSG_RESULT([yes])
       else
         AC_MSG_RESULT([no])
         _am_tools=none