Merge branch 'ds/revision-maximal-only'

"git rev-list" and friends learn "--maximal-only" to show only the
commits that are not reachable by other commits.

* ds/revision-maximal-only:
  revision: add --maximal-only option

Documentation/rev-list-options.adoc

@@ -148,6 +148,10 @@ endif::git-log[]
 	from the point where it diverged from the remote branch, given
 	that arbitrary merges can be valid topic branch changes.
 
+`--maximal-only`::
+	Restrict the output commits to be those that are not reachable
+	from any other commits in the revision range.
+
 `--not`::
 	Reverses the meaning of the '{caret}' prefix (or lack thereof)
 	for all following revision specifiers, up to the next `--not`.

object.h

@@ -64,7 +64,7 @@ void object_array_init(struct object_array *array);
 
 /*
  * object flag allocation:
- * revision.h:               0---------10         15               23------27
+ * revision.h:               0---------10         15               23--------28
  * fetch-pack.c:             01    67
  * negotiator/default.c:       2--5
  * walker.c:                 0-2
@@ -86,7 +86,7 @@ void object_array_init(struct object_array *array);
  * builtin/unpack-objects.c:                                 2021
  * pack-bitmap.h:                                              2122
  */
-#define FLAG_BITS  28
+#define FLAG_BITS  29
 
 #define TYPE_BITS 3
 

revision.c

@@ -1150,7 +1150,8 @@ static int process_parents(struct rev_info *revs, struct commit *commit,
 			struct commit *p = parent->item;
 			parent = parent->next;
 			if (p)
-				p->object.flags |= UNINTERESTING;
+				p->object.flags |= UNINTERESTING |
+						   CHILD_VISITED;
 			if (repo_parse_commit_gently(revs->repo, p, 1) < 0)
 				continue;
 			if (p->parents)
@@ -1204,7 +1205,7 @@ static int process_parents(struct rev_info *revs, struct commit *commit,
 			if (!*slot)
 				*slot = *revision_sources_at(revs->sources, commit);
 		}
-		p->object.flags |= pass_flags;
+		p->object.flags |= pass_flags | CHILD_VISITED;
 		if (!(p->object.flags & SEEN)) {
 			p->object.flags |= (SEEN | NOT_USER_GIVEN);
 			if (list)
@@ -2377,6 +2378,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	} else if ((argcount = parse_long_opt("until", argv, &optarg))) {
 		revs->min_age = approxidate(optarg);
 		return argcount;
+	} else if (!strcmp(arg, "--maximal-only")) {
+		revs->maximal_only = 1;
 	} else if (!strcmp(arg, "--first-parent")) {
 		revs->first_parent_only = 1;
 	} else if (!strcmp(arg, "--exclude-first-parent-only")) {
@@ -3147,6 +3150,9 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 				  !!revs->reverse, "--reverse",
 				  !!revs->reflog_info, "--walk-reflogs");
 
+	die_for_incompatible_opt2(!!revs->boundary, "--boundary",
+				  !!revs->maximal_only, "--maximal-only");
+
 	if (revs->no_walk && revs->graph)
 		die(_("options '%s' and '%s' cannot be used together"), "--no-walk", "--graph");
 	if (!revs->reflog_info && revs->grep_filter.use_reflog_filter)
@@ -4125,6 +4131,8 @@ enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi
 {
 	if (commit->object.flags & SHOWN)
 		return commit_ignore;
+	if (revs->maximal_only && (commit->object.flags & CHILD_VISITED))
+		return commit_ignore;
 	if (revs->unpacked && has_object_pack(revs->repo, &commit->object.oid))
 		return commit_ignore;
 	if (revs->no_kept_objects) {

revision.h

@@ -52,7 +52,9 @@
 #define NOT_USER_GIVEN	(1u<<25)
 #define TRACK_LINEAR	(1u<<26)
 #define ANCESTRY_PATH	(1u<<27)
-#define ALL_REV_FLAGS	(((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR | PULL_MERGE)
+#define CHILD_VISITED	(1u<<28)
+#define ALL_REV_FLAGS	(((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR \
+				      | PULL_MERGE | CHILD_VISITED)
 
 #define DECORATE_SHORT_REFS	1
 #define DECORATE_FULL_REFS	2
@@ -189,6 +191,7 @@ struct rev_info {
 			left_right:1,
 			left_only:1,
 			right_only:1,
+			maximal_only:1,
 			rewrite_parents:1,
 			print_parents:1,
 			show_decorations:1,

t/t6000-rev-list-misc.sh

@@ -248,4 +248,19 @@ test_expect_success 'rev-list -z --boundary' '
 	test_cmp expect actual
 '
 
+test_expect_success 'rev-list --boundary incompatible with --maximal-only' '
+	test_when_finished rm -rf repo &&
+
+	git init repo &&
+	test_commit -C repo 1 &&
+	test_commit -C repo 2 &&
+
+	oid1=$(git -C repo rev-parse HEAD~) &&
+	oid2=$(git -C repo rev-parse HEAD) &&
+
+	test_must_fail git -C repo rev-list --boundary --maximal-only \
+		HEAD~1..HEAD 2>err &&
+	test_grep "cannot be used together" err
+'
+
 test_done

t/t6600-test-reach.sh

@@ -762,4 +762,79 @@ test_expect_success 'for-each-ref is-base: --sort' '
 		--sort=refname --sort=-is-base:commit-2-3
 '
 
+test_expect_success 'rev-list --maximal-only (all positive)' '
+	# Only one maximal.
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-4-2
+	refs/heads/commit-4-4
+	refs/heads/commit-8-4
+	EOF
+
+	cat >expect <<-EOF &&
+	$(git rev-parse refs/heads/commit-8-4)
+	EOF
+	run_all_modes git rev-list --maximal-only --stdin &&
+
+	# All maximal.
+	cat >input <<-\EOF &&
+	refs/heads/commit-5-2
+	refs/heads/commit-4-3
+	refs/heads/commit-3-4
+	refs/heads/commit-2-5
+	EOF
+
+	cat >expect <<-EOF &&
+	$(git rev-parse refs/heads/commit-5-2)
+	$(git rev-parse refs/heads/commit-4-3)
+	$(git rev-parse refs/heads/commit-3-4)
+	$(git rev-parse refs/heads/commit-2-5)
+	EOF
+	run_all_modes git rev-list --maximal-only --stdin &&
+
+	# Mix of both.
+	cat >input <<-\EOF &&
+	refs/heads/commit-5-2
+	refs/heads/commit-3-2
+	refs/heads/commit-2-5
+	EOF
+
+	cat >expect <<-EOF &&
+	$(git rev-parse refs/heads/commit-5-2)
+	$(git rev-parse refs/heads/commit-2-5)
+	EOF
+	run_all_modes git rev-list --maximal-only --stdin
+'
+
+test_expect_success 'rev-list --maximal-only (range)' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-2-5
+	refs/heads/commit-6-4
+	^refs/heads/commit-4-5
+	EOF
+
+	cat >expect <<-EOF &&
+	$(git rev-parse refs/heads/commit-6-4)
+	EOF
+	run_all_modes git rev-list --maximal-only --stdin &&
+
+	# first-parent changes reachability: the first parent
+	# reduces the second coordinate to 1 before reducing the
+	# first coordinate.
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-2-5
+	refs/heads/commit-6-4
+	^refs/heads/commit-4-5
+	EOF
+
+	cat >expect <<-EOF &&
+	$(git rev-parse refs/heads/commit-6-4)
+	$(git rev-parse refs/heads/commit-2-5)
+	EOF
+	run_all_modes git rev-list --maximal-only --stdin \
+		--first-parent --exclude-first-parent-only
+'
+
 test_done