diff: avoid generating unused hunk header lines

Some callers of xdi_diff_outf() do not look at the generated hunk header
lines at all. By plugging in a no-op hunk callback, this tells xdiff not
to even bother formatting them.

This patch introduces a stock no-op callback and uses it with a few
callers whose line callbacks explicitly ignore hunk headers (because
they look only for +/- lines).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/diff.c b/diff.c
index f9b9adc545..d3e7262310 100644
--- a/diff.c
+++ b/diff.c
@@ -3604,8 +3604,8 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 		xpp.anchors_nr = o->anchors_nr;
 		xecfg.ctxlen = o->context;
 		xecfg.interhunkctxlen = o->interhunkcontext;
-		if (xdi_diff_outf(&mf1, &mf2, NULL, diffstat_consume,
-				  diffstat, &xpp, &xecfg))
+		if (xdi_diff_outf(&mf1, &mf2, discard_hunk_line,
+				  diffstat_consume, diffstat, &xpp, &xecfg))
 			die("unable to generate diffstat for %s", one->path);
 	}