git-rev-list: add --exclude-first-parent-only flag

It is useful to know when a branch first diverged in history
from some integration branch in order to be able to enumerate
the user's local changes. However, these local changes can
include arbitrary merges, so it is necessary to ignore this
merge structure when finding the divergence point.

In order to do this, teach the "rev-list" family to accept
"--exclude-first-parent-only", which restricts the traversal
of excluded commits to only follow first parent links.

   -A-----E-F-G--main
     \   / /
      B-C-D--topic

In this example, the goal is to return the set {B, C, D} which
represents a topic branch that has been merged into main branch.
`git rev-list topic ^main` will end up returning no commits
since excluding main will end up traversing the commits on topic
as well. `git rev-list --exclude-first-parent-only topic ^main`
however will return {B, C, D} as desired.

Add docs for the new flag, and clarify the doc for --first-parent
to indicate that it applies to traversing the set of included
commits only.

Signed-off-by: Jerry Zhang <jerry@skydio.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 20 insertions, 10 deletions

diff --git a/revision.c b/revision.c
index ad4286f..d8d326d 100644
--- a/revision.c
+++ b/revision.c
@@ -273,7 +273,7 @@ static void commit_stack_clear(struct commit_stack *stack)
 	stack->nr = stack->alloc = 0;
 }
 
-static void mark_one_parent_uninteresting(struct commit *commit,
+static void mark_one_parent_uninteresting(struct rev_info *revs, struct commit *commit,
 					  struct commit_stack *pending)
 {
 	struct commit_list *l;
@@ -290,20 +290,26 @@ static void mark_one_parent_uninteresting(struct commit *commit,
 	 * wasn't uninteresting), in which case we need
 	 * to mark its parents recursively too..
 	 */
-	for (l = commit->parents; l; l = l->next)
+	for (l = commit->parents; l; l = l->next) {
 		commit_stack_push(pending, l->item);
+		if (revs && revs->exclude_first_parent_only)
+			break;
+	}
 }
 
-void mark_parents_uninteresting(struct commit *commit)
+void mark_parents_uninteresting(struct rev_info *revs, struct commit *commit)
 {
 	struct commit_stack pending = COMMIT_STACK_INIT;
 	struct commit_list *l;
 
-	for (l = commit->parents; l; l = l->next)
-		mark_one_parent_uninteresting(l->item, &pending);
+	for (l = commit->parents; l; l = l->next) {
+		mark_one_parent_uninteresting(revs, l->item, &pending);
+		if (revs && revs->exclude_first_parent_only)
+			break;
+	}
 
 	while (pending.nr > 0)
-		mark_one_parent_uninteresting(commit_stack_pop(&pending),
+		mark_one_parent_uninteresting(revs, commit_stack_pop(&pending),
 					      &pending);
 
 	commit_stack_clear(&pending);
@@ -441,7 +447,7 @@ static struct commit *handle_commit(struct rev_info *revs,
 		if (repo_parse_commit(revs->repo, commit) < 0)
 			die("unable to parse commit %s", name);
 		if (flags & UNINTERESTING) {
-			mark_parents_uninteresting(commit);
+			mark_parents_uninteresting(revs, commit);
 
 			if (!revs->topo_order || !generation_numbers_enabled(the_repository))
 				revs->limited = 1;
@@ -1124,7 +1130,7 @@ static int process_parents(struct rev_info *revs, struct commit *commit,
 			if (repo_parse_commit_gently(revs->repo, p, 1) < 0)
 				continue;
 			if (p->parents)
-				mark_parents_uninteresting(p);
+				mark_parents_uninteresting(revs, p);
 			if (p->object.flags & SEEN)
 				continue;
 			p->object.flags |= (SEEN | NOT_USER_GIVEN);
@@ -1132,6 +1138,8 @@ static int process_parents(struct rev_info *revs, struct commit *commit,
 				commit_list_insert_by_date(p, list);
 			if (queue)
 				prio_queue_put(queue, p);
+			if (revs->exclude_first_parent_only)
+				break;
 		}
 		return 0;
 	}
@@ -1422,7 +1430,7 @@ static int limit_list(struct rev_info *revs)
 		if (process_parents(revs, commit, &original_list, NULL) < 0)
 			return -1;
 		if (obj->flags & UNINTERESTING) {
-			mark_parents_uninteresting(commit);
+			mark_parents_uninteresting(revs, commit);
 			slop = still_interesting(original_list, date, slop, &interesting_cache);
 			if (slop)
 				continue;
@@ -2223,6 +2231,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		return argcount;
 	} else if (!strcmp(arg, "--first-parent")) {
 		revs->first_parent_only = 1;
+	} else if (!strcmp(arg, "--exclude-first-parent-only")) {
+		revs->exclude_first_parent_only = 1;
 	} else if (!strcmp(arg, "--ancestry-path")) {
 		revs->ancestry_path = 1;
 		revs->simplify_history = 0;
@@ -3345,7 +3355,7 @@ static void explore_walk_step(struct rev_info *revs)
 		return;
 
 	if (c->object.flags & UNINTERESTING)
-		mark_parents_uninteresting(c);
+		mark_parents_uninteresting(revs, c);
 
 	for (p = c->parents; p; p = p->next)
 		test_flag_and_insert(&info->explore_queue, p->item, TOPO_WALK_EXPLORED);