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, 3 insertions, 0 deletions

diff --git a/list-objects.c b/list-objects.c
index 47296dff2f..f4e1104b56 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -389,6 +389,9 @@ static void do_traverse(struct traversal_context *ctx)
 		 */
 		if (!ctx->revs->tree_objects)
 			; /* do not bother loading tree */
+		else if (ctx->revs->do_not_die_on_missing_objects &&
+			 oidset_contains(&ctx->revs->missing_commits, &commit->object.oid))
+			;
 		else if (repo_get_commit_tree(the_repository, commit)) {
 			struct tree *tree = repo_get_commit_tree(the_repository,
 								 commit);