range-diff: optionally accept pathspecs

The `git range-diff` command can be quite expensive, which is not a
surprise given that the underlying algorithm to match up pairs of
commits between the provided two commit ranges has a cubic runtime.

Therefore it makes sense to restrict the commit ranges as much as
possible, to reduce the amount of input to that O(N^3) algorithm.

In chatty repositories with wide trees, this is not necessarily
possible merely by choosing commit ranges wisely.

Let's give users another option to restrict the commit ranges: by
providing a pathspec. That helps in repositories with wide trees because
it is likely that the user has a good idea which subset of the tree they
are actually interested in.

Example:

	git range-diff upstream/main upstream/seen HEAD -- range-diff.c

This shows commits that are either in the local branch or in `seen`, but
not in `main`, skipping all commits that do not touch `range-diff.c`.

Note: Since we piggy-back the pathspecs onto the `other_arg` mechanism
that was introduced to be able to pass through the `--notes` option to
the revision machinery, we must now ensure that the `other_arg` array is
appended at the end (the revision range must come before the pathspecs,
if any).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/range-diff.c

@@ -38,9 +38,10 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 	struct option *options;
-	int res = 0;
+	int i, dash_dash = -1, res = 0;
 	struct strbuf range1 = STRBUF_INIT, range2 = STRBUF_INIT;
 	struct object_id oid;
+	const char *three_dots = NULL;
 
 	git_config(git_diff_ui_config, NULL);
 
@@ -48,7 +49,7 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 
 	options = parse_options_concat(range_diff_options, diffopt.parseopts);
 	argc = parse_options(argc, argv, prefix, options,
-			     builtin_range_diff_usage, 0);
+			     builtin_range_diff_usage, PARSE_OPT_KEEP_DASHDASH);
 
 	diff_setup_done(&diffopt);
 
@@ -56,8 +57,20 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 	if (!simple_color)
 		diffopt.use_color = 1;
 
-	if (argc == 3) {
-		if (get_oid_committish(argv[0], &oid))
+	for (i = 0; i < argc; i++)
+		if (!strcmp(argv[i], "--")) {
+			dash_dash = i;
+			break;
+		}
+
+	if (dash_dash == 3 ||
+	    (dash_dash < 0 && argc > 2 &&
+	     !get_oid_committish(argv[0], &oid) &&
+	     !get_oid_committish(argv[1], &oid) &&
+	     !get_oid_committish(argv[2], &oid))) {
+		if (dash_dash < 0)
+			; /* already validated arguments */
+		else if (get_oid_committish(argv[0], &oid))
 			usage_msg_optf(_("not a revision: '%s'"),
 				       builtin_range_diff_usage, options,
 				       argv[0]);
@@ -72,8 +85,16 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 
 		strbuf_addf(&range1, "%s..%s", argv[0], argv[1]);
 		strbuf_addf(&range2, "%s..%s", argv[0], argv[2]);
-	} else if (argc == 2) {
-		if (!is_range_diff_range(argv[0]))
+
+		strvec_pushv(&other_arg, argv +
+			     (dash_dash < 0 ? 3 : dash_dash));
+	} else if (dash_dash == 2 ||
+		   (dash_dash < 0 && argc > 1 &&
+		    is_range_diff_range(argv[0]) &&
+		    is_range_diff_range(argv[1]))) {
+		if (dash_dash < 0)
+			; /* already validated arguments */
+		else if (!is_range_diff_range(argv[0]))
 			usage_msg_optf(_("not a commit range: '%s'"),
 				       builtin_range_diff_usage, options,
 				       argv[0]);
@@ -84,25 +105,40 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 
 		strbuf_addstr(&range1, argv[0]);
 		strbuf_addstr(&range2, argv[1]);
-	} else if (argc == 1) {
-		const char *b = strstr(argv[0], "..."), *a = argv[0];
+
+		strvec_pushv(&other_arg, argv +
+			     (dash_dash < 0 ? 2 : dash_dash));
+	} else if (dash_dash == 1 ||
+		   (dash_dash < 0 && argc > 0 &&
+		    (three_dots = strstr(argv[0], "...")))) {
+		const char *a, *b;
 		int a_len;
 
-		if (!b)
+		if (dash_dash < 0)
+			; /* already validated arguments */
+		else if (!(three_dots = strstr(argv[0], "...")))
 			usage_msg_optf(_("not a symmetric range: '%s'"),
-				       builtin_range_diff_usage, options,
-				       argv[0]);
+					 builtin_range_diff_usage, options,
+					 argv[0]);
 
-		a_len = (int)(b - a);
-		if (!a_len) {
+		if (three_dots == argv[0]) {
 			a = "HEAD";
 			a_len = strlen(a);
+		} else {
+			a = argv[0];
+			a_len = (int)(three_dots - a);
 		}
-		b += 3;
-		if (!*b)
+
+		if (three_dots[3])
+			b = three_dots + 3;
+		else
 			b = "HEAD";
+
 		strbuf_addf(&range1, "%s..%.*s", b, a_len, a);
 		strbuf_addf(&range2, "%.*s..%s", a_len, a, b);
+
+		strvec_pushv(&other_arg, argv +
+			     (dash_dash < 0 ? 1 : dash_dash));
 	} else
 		usage_msg_opt(_("need two commit ranges"),
 			      builtin_range_diff_usage, options);