range-diff: offer --left-only/--right-only options

When comparing commit ranges, one is frequently interested only in one
side, such as asking the question "Has this patch that I submitted to
the Git mailing list been applied?": one would only care about the part
of the output that corresponds to the commits in a local branch.

To make that possible, imitate the `git rev-list` options `--left-only`
and `--right-only`.

This addresses https://github.com/gitgitgadget/git/issues/206

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

Documentation/git-range-diff.txt

@@ -10,6 +10,7 @@ SYNOPSIS
 [verse]
 'git range-diff' [--color=[<when>]] [--no-color] [<diff-options>]
 	[--no-dual-color] [--creation-factor=<factor>]
+	[--left-only | --right-only]
 	( <range1> <range2> | <rev1>...<rev2> | <base> <rev1> <rev2> )
 
 DESCRIPTION
@@ -57,6 +58,14 @@ to revert to color all lines according to the outer diff markers
 	See the ``Algorithm`` section below for an explanation why this is
 	needed.
 
+--left-only::
+	Suppress commits that are missing from the first specified range
+	(or the "left range" when using the `<rev1>...<rev2>` format).
+
+--right-only::
+	Suppress commits that are missing from the second specified range
+	(or the "right range" when using the `<rev1>...<rev2>` format).
+
 --[no-]notes[=<ref>]::
 	This flag is passed to the `git log` program
 	(see linkgit:git-log[1]) that generates the patches.

builtin/range-diff.c

@@ -20,7 +20,7 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 		.diffopt = &diffopt,
 		.other_arg = &other_arg
 	};
-	int simple_color = -1;
+	int simple_color = -1, left_only = 0, right_only = 0;
 	struct option range_diff_options[] = {
 		OPT_INTEGER(0, "creation-factor",
 			    &range_diff_opts.creation_factor,
@@ -30,6 +30,10 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 		OPT_PASSTHRU_ARGV(0, "notes", &other_arg,
 				  N_("notes"), N_("passed to 'git log'"),
 				  PARSE_OPT_OPTARG),
+		OPT_BOOL(0, "left-only", &left_only,
+			 N_("only emit output related to the first range")),
+		OPT_BOOL(0, "right-only", &right_only,
+			 N_("only emit output related to the second range")),
 		OPT_END()
 	};
 	struct option *options;
@@ -87,6 +91,8 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 	FREE_AND_NULL(options);
 
 	range_diff_opts.dual_color = simple_color < 1;
+	range_diff_opts.left_only = left_only;
+	range_diff_opts.right_only = right_only;
 	res = show_range_diff(range1.buf, range2.buf, &range_diff_opts);
 
 	strvec_clear(&other_arg);

range-diff.c

@@ -513,6 +513,7 @@ static void output(struct string_list *a, struct string_list *b,
 
 		/* Show unmatched LHS commit whose predecessors were shown. */
 		if (i < a->nr && a_util->matching < 0) {
+			if (!range_diff_opts->right_only)
 				output_pair_header(&opts, patch_no_width,
 					   &buf, &dashes, a_util, NULL);
 			i++;
@@ -521,6 +522,7 @@ static void output(struct string_list *a, struct string_list *b,
 
 		/* Show unmatched RHS commits. */
 		while (j < b->nr && b_util->matching < 0) {
+			if (!range_diff_opts->left_only)
 				output_pair_header(&opts, patch_no_width,
 					   &buf, &dashes, NULL, b_util);
 			b_util = ++j < b->nr ? b->items[j].util : NULL;
@@ -551,7 +553,10 @@ int show_range_diff(const char *range1, const char *range2,
 	struct string_list branch1 = STRING_LIST_INIT_DUP;
 	struct string_list branch2 = STRING_LIST_INIT_DUP;
 
-	if (read_patches(range1, &branch1, range_diff_opts->other_arg))
+	if (range_diff_opts->left_only && range_diff_opts->right_only)
+		res = error(_("--left-only and --right-only are mutually exclusive"));
+
+	if (!res && read_patches(range1, &branch1, range_diff_opts->other_arg))
 		res = error(_("could not parse log for '%s'"), range1);
 	if (!res && read_patches(range2, &branch2, range_diff_opts->other_arg))
 		res = error(_("could not parse log for '%s'"), range2);

range-diff.h

@@ -9,6 +9,7 @@
 struct range_diff_options {
 	int creation_factor;
 	unsigned dual_color:1;
+	unsigned left_only:1, right_only:1;
 	const struct diff_options *diffopt; /* may be NULL */
 	const struct strvec *other_arg; /* may be NULL */
 };

t/t3206-range-diff.sh

@@ -717,4 +717,19 @@ test_expect_success 'format-patch --range-diff with multiple notes' '
 	test_cmp expect actual
 '
 
+test_expect_success '--left-only/--right-only' '
+	git switch --orphan left-right &&
+	test_commit first &&
+	test_commit unmatched &&
+	test_commit common &&
+	git switch -C left-right first &&
+	git cherry-pick common &&
+
+	git range-diff -s --left-only ...common >actual &&
+	head_oid=$(git rev-parse --short HEAD) &&
+	common_oid=$(git rev-parse --short common) &&
+	echo "1:  $head_oid = 2:  $common_oid common" >expect &&
+	test_cmp expect actual
+'
+
 test_done