From 3b40a090fd4e441e88897dfa96f50039952ed45b Mon Sep 17 00:00:00 2001
From: Jeff King <peff@peff.net>
Date: Fri, 2 Nov 2018 02:36:06 -0400
Subject: 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>

diff --git a/diff.c b/diff.c
index f9b9adc..d3e7262 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);
 	}
 
diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index 7609bb4..25e1214 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -62,7 +62,8 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	ecbdata.hit = 0;
 	xecfg.ctxlen = o->context;
 	xecfg.interhunkctxlen = o->interhunkcontext;
-	if (xdi_diff_outf(one, two, NULL, diffgrep_consume, &ecbdata, &xpp, &xecfg))
+	if (xdi_diff_outf(one, two, discard_hunk_line, diffgrep_consume,
+			  &ecbdata, &xpp, &xecfg))
 		return 0;
 	return ecbdata.hit;
 }
diff --git a/xdiff-interface.c b/xdiff-interface.c
index eb9c05a..b99a578 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -157,6 +157,12 @@ int xdi_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp, xdemitconf_t co
 	return xdl_diff(&a, &b, xpp, xecfg, xecb);
 }
 
+void discard_hunk_line(void *priv,
+		       long ob, long on, long nb, long nn,
+		       const char *func, long funclen)
+{
+}
+
 int xdi_diff_outf(mmfile_t *mf1, mmfile_t *mf2,
 		  xdiff_emit_hunk_fn hunk_fn,
 		  xdiff_emit_line_fn line_fn,
diff --git a/xdiff-interface.h b/xdiff-interface.h
index 2dbe2fe..8af245e 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -36,6 +36,14 @@ extern int git_xmerge_config(const char *var, const char *value, void *cb);
 extern int git_xmerge_style;
 
 /*
+ * Can be used as a no-op hunk_fn for xdi_diff_outf(), since a NULL
+ * one just sends the hunk line to the line_fn callback).
+ */
+void discard_hunk_line(void *priv,
+		       long ob, long on, long nb, long nn,
+		       const char *func, long funclen);
+
+/*
  * Compare the strings l1 with l2 which are of size s1 and s2 respectively.
  * Returns 1 if the strings are deemed equal, 0 otherwise.
  * The `flags` given as XDF_WHITESPACE_FLAGS determine how white spaces
-- 
cgit v0.10.2-6-g49f6