gnulib-tool: Fail properly if the 'join' program is not found.

Reported by Simon Josefsson <simon@josefsson.org> in
<https://lists.gnu.org/archive/html/bug-gnulib/2021-05/msg00029.html>.

* gnulib-tool: Bail out early of the 'join' program is not found.

1 files changed, 9 insertions, 0 deletions

diff --git a/gnulib-tool b/gnulib-tool
index 182b9b4a4e..9b5c81529c 100755
--- a/gnulib-tool
+++ b/gnulib-tool
@@ -888,6 +888,15 @@ func_hardlink ()
   }
 }
 
+# The 'join' program does not exist on all platforms.  Where it exists,
+# we can use it.  Where not, bail out.
+if (type join) >/dev/null 2>&1; then
+  :
+else
+  echo "$progname: 'join' program not found. Consider installing GNU coreutils." >&2
+  func_exit 1
+fi
+
 # Ensure an 'echo' command that
 #   1. does not interpret backslashes and
 #   2. does not print an error message "broken pipe" when writing into a pipe