diff: don't crash with empty argument to -G or -S

The pickaxe options, -G and -S, need either a regex or a string to look
through the history for.  An empty value isn't very useful since it
would either match everything or nothing, and what's worse, we presently
crash with a BUG like so when the user provides one:

    BUG: diffcore-pickaxe.c:241: should have needle under -G or -S

Since it's not very nice of us to crash and this wouldn't do anything
useful anyway, let's simply inform the user that they must provide a
non-empty argument and exit with an error if they provide an empty one
instead.

Reported-by: Jared Van Bortel <cebtenzzre@gmail.com>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Acked-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/diff.c b/diff.c
index d28b4114c8..5a26300ec4 100644
--- a/diff.c
+++ b/diff.c
@@ -5493,6 +5493,8 @@ static int diff_opt_pickaxe_regex(const struct option *opt,
 	BUG_ON_OPT_NEG(unset);
 	options->pickaxe = arg;
 	options->pickaxe_opts |= DIFF_PICKAXE_KIND_G;
+	if (arg && !*arg)
+		return error(_("-G requires a non-empty argument"));
 	return 0;
 }
 
@@ -5504,6 +5506,8 @@ static int diff_opt_pickaxe_string(const struct option *opt,
 	BUG_ON_OPT_NEG(unset);
 	options->pickaxe = arg;
 	options->pickaxe_opts |= DIFF_PICKAXE_KIND_S;
+	if (arg && !*arg)
+		return error(_("-S requires a non-empty argument"));
 	return 0;
 }