range-diff: let '--abbrev' option takes effect

As mentioned in 'git-range-diff.txt': "`git range-diff` also accepts the
regular diff options (see linkgit:git-diff[1])...", but '--abbrev' is not
in the "regular" scope.

In Git, the "abbrev" of an object may not be a fixed value in different
repositories, depending on the needs of the them(Linus mentioned in
e6c587c7 in 2016: "the Linux kernel project needs 11 to 12 hexdigits"
at that time ), that's why a user may want to display abbrev according
to a specified length.

Although a similar effect can be achieved through configuration (like:
git -c core.abbrev=<abbrev>), but based on ease of use (many users may not
know that the -c option can be specified) and the description in existing
document, supporting users to directly use '--abbrev', could be a good way.

Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

range-diff.c

@@ -383,11 +383,14 @@ static void output_pair_header(struct diff_options *diffopt,
 	const char *color_new = diff_get_color_opt(diffopt, DIFF_FILE_NEW);
 	const char *color_commit = diff_get_color_opt(diffopt, DIFF_COMMIT);
 	const char *color;
+	char abbrev = diffopt->abbrev;
+
+	if (abbrev < 0)
+		abbrev = DEFAULT_ABBREV;
 
 	if (!dashes->len)
 		strbuf_addchars(dashes, '-',
-				strlen(find_unique_abbrev(oid,
+				strlen(find_unique_abbrev(oid, abbrev)));
-							  DEFAULT_ABBREV)));
 
 	if (!b_util) {
 		color = color_old;
@@ -409,7 +412,7 @@ static void output_pair_header(struct diff_options *diffopt,
 		strbuf_addf(buf, "%*s:  %s ", patch_no_width, "-", dashes->buf);
 	else
 		strbuf_addf(buf, "%*d:  %s ", patch_no_width, a_util->i + 1,
-			    find_unique_abbrev(&a_util->oid, DEFAULT_ABBREV));
+			    find_unique_abbrev(&a_util->oid, abbrev));
 
 	if (status == '!')
 		strbuf_addf(buf, "%s%s", color_reset, color);
@@ -421,7 +424,7 @@ static void output_pair_header(struct diff_options *diffopt,
 		strbuf_addf(buf, " %*s:  %s", patch_no_width, "-", dashes->buf);
 	else
 		strbuf_addf(buf, " %*d:  %s", patch_no_width, b_util->i + 1,
-			    find_unique_abbrev(&b_util->oid, DEFAULT_ABBREV));
+			    find_unique_abbrev(&b_util->oid, abbrev));
 
 	commit = lookup_commit_reference(the_repository, oid);
 	if (commit) {

t/t3206-range-diff.sh

@@ -33,6 +33,26 @@ test_expect_success 'setup' '
 	u3 sha256:736c4bc
 	u4 sha256:673e77d
 
+	# topic (abbrev=10)
+	t1_abbrev sha1:4de457d2c0
+	t2_abbrev sha1:fccce22f8c
+	t3_abbrev sha1:147e64ef53
+	t4_abbrev sha1:a63e992599
+	t1_abbrev sha256:b89f8b9092
+	t2_abbrev sha256:5f12aadf34
+	t3_abbrev sha256:ea8b273a6c
+	t4_abbrev sha256:14b73361fc
+
+	# unmodified (abbrev=10)
+	u1_abbrev sha1:35b9b25f76
+	u2_abbrev sha1:de345ab3de
+	u3_abbrev sha1:9af6654000
+	u4_abbrev sha1:2901f773f3
+	u1_abbrev sha256:e3731be242
+	u2_abbrev sha256:14fadf8cee
+	u3_abbrev sha256:736c4bcb44
+	u4_abbrev sha256:673e77d589
+
 	# reordered
 	r1 sha1:aca177a
 	r2 sha1:14ad629
@@ -153,6 +173,18 @@ test_expect_success 'simple A B C (unmodified)' '
 	test_cmp expect actual
 '
 
+test_expect_success 'simple A..B A..C (unmodified) with --abbrev' '
+	git range-diff --no-color --abbrev=10 main..topic main..unmodified \
+		>actual &&
+	cat >expect <<-EOF &&
+	1:  $(test_oid t1_abbrev) = 1:  $(test_oid u1_abbrev) s/5/A/
+	2:  $(test_oid t2_abbrev) = 2:  $(test_oid u2_abbrev) s/4/A/
+	3:  $(test_oid t3_abbrev) = 3:  $(test_oid u3_abbrev) s/11/B/
+	4:  $(test_oid t4_abbrev) = 4:  $(test_oid u4_abbrev) s/12/B/
+	EOF
+	test_cmp expect actual
+'
+
 test_expect_success 'A^! and A^-<n> (unmodified)' '
 	git range-diff --no-color topic^! unmodified^-1 >actual &&
 	cat >expect <<-EOF &&