[PATCH 01/12] diffstat_consume(): assert non-zero length

From: Jeff King <peff@peff.net>
Date: Oct 18, 2022, 01:01 UTC
Message-ID: <Y0363eQnvcNkCG/O@coredump.intra.peff.net>
In-Reply-To: <Y036whEorZV0rOgB@coredump.intra.peff.net>

The callback interface for xdiff_emit_line_fn gives us a line/len pair, but diffstat_consume() never looks at "len". At first glance this seems like a bug that could cause us to read further than xdiff intends. But in practice, we read only the first character, and xdiff would never pass us an empty line.

Let's add a run-time assertion that this is true, which clarifies our assumption and silences -Wunused-parameter.

Signed-off-by: Jeff King <peff@peff.net>
---
 diff.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/diff.c b/diff.c
index 648f6717a5..bba888a34a 100644
--- a/diff.c
+++ b/diff.c
@@ -2488,6 +2488,9 @@ static int diffstat_consume(void *priv, char *line, unsigned long len)
 	struct diffstat_t *diffstat = priv;
 	struct diffstat_file *x = diffstat->files[diffstat->nr - 1];
 
+	if (!len)
+		BUG("xdiff fed us an empty line");
+
 	if (line[0] == '+')
 		x->added++;
 	else if (line[0] == '-')

-- 
2.38.0.371.g300879f34e