[PATCH v2 0/3] Don't lazy-fetch commits when parsing them

Thanks everyone for taking a look. In the end, I thought it best to bite the bullet and move all the corruption diagnostics to where they are detected instead of re-checking (and thus relying on errno to be preserved) after we have found out that we couldn't read the object. This does mean a reworking of all the earlier patches, but overall I think that this puts the code in a better state.

I have also verified that this passes CI [1].

[1] https://github.com/jonathantanmy/git/actions/runs/3634359088

Jonathan Tan (3):
  object-file: don't exit early if skipping loose
  object-file: emit corruption errors when detected
  commit: don't lazy-fetch commits

 commit.c       | 15 +++++++--
 object-file.c  | 84 ++++++++++++++++++++++++++------------------------
 object-store.h |  3 ++
 3 files changed, 59 insertions(+), 43 deletions(-)

Range-diff against v1:
1:  3a00bc45fd < -:  ---------- object-file: reread object with exact same args
2:  9999e127a0 < -:  ---------- object-file: refactor corrupt object diagnosis
3:  28c7ee2f8c < -:  ---------- object-file: refactor replace object lookup
-:  ---------- > 1:  9ad34a1dce object-file: don't exit early if skipping loose
-:  ---------- > 2:  9ddfff3585 object-file: emit corruption errors when detected
4:  0607fa67d1 ! 3:  c5fe42deb0 commit: don't lazy-fetch commits
    @@ commit.c: int repo_parse_commit_internal(struct repository *r,
      	enum object_type type;
      	void *buffer;
      	unsigned long size;
    -+	const struct object_id *real_oid;
     +	struct object_info oi = {
     +		.typep = &type,
     +		.sizep = &size,
     +		.contentp = &buffer,
    -+		.real_oidp = &real_oid,
     +	};
    ++	/*
    ++	 * Git does not support partial clones that exclude commits, so set
    ++	 * OBJECT_INFO_SKIP_FETCH_OBJECT to fail fast when an object is missing.
    ++	 */
    ++	int flags = OBJECT_INFO_LOOKUP_REPLACE | OBJECT_INFO_SKIP_FETCH_OBJECT |
    ++		OBJECT_INFO_DIE_IF_CORRUPT;
      	int ret;
      
      	if (!item)
    @@ commit.c: int repo_parse_commit_internal(struct repository *r,
     -	buffer = repo_read_object_file(r, &item->object.oid, &type, &size);
     -	if (!buffer)
     +
    -+	/*
    -+	 * Git does not support partial clones that exclude commits, so set
    -+	 * OBJECT_INFO_SKIP_FETCH_OBJECT to fail fast when an object is missing.
    -+	 */
    -+	if (oid_object_info_extended(r, &item->object.oid, &oi,
    -+	    OBJECT_INFO_LOOKUP_REPLACE | OBJECT_INFO_SKIP_FETCH_OBJECT) < 0) {
    -+		die_if_corrupt(r, &item->object.oid, real_oid);
    ++	if (oid_object_info_extended(r, &item->object.oid, &oi, flags) < 0)
      		return quiet_on_missing ? -1 :
      			error("Could not read %s",
      			     oid_to_hex(&item->object.oid));
    -+	}
    - 	if (type != OBJ_COMMIT) {
    - 		free(buffer);
    - 		return error("Object %s not a commit",