xdiff users: use designated initializers for out_line

Amend the code added in 611e42a (xdiff: provide a separate emit
callback for hunks, 2018-11-02) to be more readable by using
designated initializers.

This changes "priv" in rerere.c to be initialized to NULL as we did in
merge-tree.c. That's not needed as we'll only use it if the callback
is defined, but being consistent here is better and less verbose.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: avar

builtin/merge-tree.c

@@ -107,15 +107,12 @@ static void show_diff(struct merge_list *entry)
 	mmfile_t src, dst;
 	xpparam_t xpp;
 	xdemitconf_t xecfg;
-	xdemitcb_t ecb;
+	xdemitcb_t ecb = { .out_line = show_outf };
 
 	memset(&xpp, 0, sizeof(xpp));
 	xpp.flags = 0;
 	memset(&xecfg, 0, sizeof(xecfg));
 	xecfg.ctxlen = 3;
-	ecb.out_hunk = NULL;
-	ecb.out_line = show_outf;
-	ecb.priv = NULL;
 
 	src.ptr = origin(entry, &size);
 	if (!src.ptr)

builtin/rerere.c

@@ -28,7 +28,7 @@ static int diff_two(const char *file1, const char *label1,
 {
 	xpparam_t xpp;
 	xdemitconf_t xecfg;
-	xdemitcb_t ecb;
+	xdemitcb_t ecb = { .out_line = outf };
 	mmfile_t minus, plus;
 	int ret;
 
@@ -41,8 +41,6 @@ static int diff_two(const char *file1, const char *label1,
 	xpp.flags = 0;
 	memset(&xecfg, 0, sizeof(xecfg));
 	xecfg.ctxlen = 3;
-	ecb.out_hunk = NULL;
-	ecb.out_line = outf;
 	ret = xdi_diff(&minus, &plus, &xpp, &xecfg, &ecb);
 
 	free(minus.ptr);