rev-list: add commit object support in `--missing` option

The `--missing` object option in rev-list currently works only with
missing blobs/trees. For missing commits the revision walker fails with
a fatal error.

Let's extend the functionality of `--missing` option to also support
commit objects. This is done by adding a `missing_objects` field to
`rev_info`. This field is an `oidset` to which we'll add the missing
commits as we encounter them. The revision walker will now continue the
traversal and call `show_commit()` even for missing commits. In rev-list
we can then check if the commit is a missing commit and call the
existing code for parsing `--missing` objects.

A scenario where this option would be used is to find the boundary
objects between different object directories. Consider a repository with
a main object directory (GIT_OBJECT_DIRECTORY) and one or more alternate
object directories (GIT_ALTERNATE_OBJECT_DIRECTORIES). In such a
repository, using the `--missing=print` option while disabling the
alternate object directory allows us to find the boundary objects
between the main and alternate object directory.

Helped-by: Patrick Steinhardt <ps@pks.im>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/builtin/rev-list.c b/builtin/rev-list.c
index 98542e8b3c..181353dcf5 100644
--- a/builtin/rev-list.c
+++ b/builtin/rev-list.c
@@ -149,6 +149,12 @@ static void show_commit(struct commit *commit, void *data)
 
 	display_progress(progress, ++progress_counter);
 
+	if (revs->do_not_die_on_missing_objects &&
+	    oidset_contains(&revs->missing_commits, &commit->object.oid)) {
+		finish_object__ma(&commit->object);
+		return;
+	}
+
 	if (show_disk_usage)
 		total_disk_usage += get_object_disk_usage(&commit->object);