archive-tar: report filter start error only once

A missing tar filter is reported by start_command() using error(), but
also by its caller, write_tar_filter_archive(), using die():

   $ git -c tar.invalid.command=foo archive --format=invalid HEAD
   error: cannot run foo: No such file or directory
   fatal: unable to start 'foo' filter: No such file or directory

The second message contains all relevant information and even says that
the failed command was intended to be used as a filter.  Silence the
first one because it's redundant.

Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Taylor Blau <[email protected]>

Author: rscharfe

archive-tar.c

@@ -498,6 +498,7 @@ static int write_tar_filter_archive(const struct archiver *ar,
 	strvec_push(&filter.args, cmd.buf);
 	filter.use_shell = 1;
 	filter.in = -1;
+	filter.silent_exec_failure = 1;
 
 	if (start_command(&filter) < 0)
 		die_errno(_("unable to start '%s' filter"), cmd.buf);

t/t5000-tar-tree.sh

@@ -342,6 +342,13 @@ test_expect_success 'only enabled filters are available remotely' '
 	test_cmp_bin remote.bar config.bar
 '
 
+test_expect_success 'invalid filter is reported only once' '
+	test_must_fail git -c tar.invalid.command= archive --format=invalid \
+		HEAD >out 2>err &&
+	test_must_be_empty out &&
+	test_line_count = 1 err
+'
+
 test_expect_success 'git archive --format=tgz' '
 	git archive --format=tgz HEAD >j.tgz
 '