[PATCH 12/16] stat_opt: check extra strlen call

As in earlier commits, the diff option parser uses
starts_with to find that an argument starts with "--stat-",
and then adds strlen("stat-") to find the rest of the
option.

However, in this case the starts_with and the strlen are
separated across functions, making it easy to call the
latter without the former. Let's use skip_prefix instead of
raw pointer arithmetic to catch such a case.

Signed-off-by: Jeff King <redacted>
---
Another possibility would be for stat_opt to take only the
prefix-skipped part of the string. But that would involve refactoring
its use of "av" (it needs the whole array because it may need to grab a
follow-on argument).

 diff.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/diff.c b/diff.c
index 2378ae4..06bdfb8 100644
--- a/diff.c
+++ b/diff.c

@@ -3422,7 +3422,8 @@ static int stat_opt(struct diff_options *options, const char **av)
 	int count = options->stat_count;
 	int argcount = 1;
 
-	arg += strlen("--stat");
+	if (!skip_prefix(arg, "--stat", &arg))
+		die("BUG: stat option does not begin with --stat: %s", arg);
 	end = (char *)arg;
 
 	switch (*arg) {

-- 
2.0.0.566.gfe3e6b2