for-each-repo: do nothing on empty config

'git for-each-repo --config=X' should return success without calling any
subcommands when the config key 'X' has no value. The current
implementation instead segfaults.

A user could run into this issue if they used 'git maintenance start' to
initialize their cron schedule using 'git for-each-repo
--config=maintenance.repo ...' but then using 'git maintenance
unregister' to remove the config option. (Note: 'git maintenance stop'
would remove the config _and_ remove the cron schedule.)

Add a simple test to ensure this works. Use 'git help --no-such-option'
as the potential subcommand to ensure that we will hit a failure if the
subcommand is ever run.

Reported-by: Andreas Bühmann <dev@uuml.de>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/builtin/for-each-repo.c b/builtin/for-each-repo.c
index 5bba623ff1..52be64a437 100644
--- a/builtin/for-each-repo.c
+++ b/builtin/for-each-repo.c
@@ -51,6 +51,13 @@ int cmd_for_each_repo(int argc, const char **argv, const char *prefix)
 	values = repo_config_get_value_multi(the_repository,
 					     config_key);
 
+	/*
+	 * Do nothing on an empty list, which is equivalent to the case
+	 * where the config variable does not exist at all.
+	 */
+	if (!values)
+		return 0;
+
 	for (i = 0; !result && i < values->nr; i++)
 		result = run_command_on_repo(values->items[i].string, &args);