[PATCH v3 0/3] rev-list: add support for commits in `--missing`

The `--missing` option in git-rev-list(1) was introduced intitally to deal with missing blobs in the context of promissory notes. Eventually the option was extended to also support tree objects in 7c0fe330d5 (rev-list: handle missing tree objects properly,2018-10-05).

This patch series extends the `--missing` option to also add support for commit objects. We do this by introducing a new flag `MISSING` which is added whenever we encounter a missing commit during traversal. Then in `builtin/rev-list` we check for this flag and take the appropriate action based on the `--missing=*` option used.

This series is an alternate to the patch series I had posted earlier: https://lore.kernel.org/git/20230908174208.249184-1-karthik.188@gmail.com/. In that patch, we introduced an option `--ignore-missing-links` which was added to expose the `ignore_missing_links` bit to the user. The issue in that patch was that, the option `--ignore-missing-links` didn't play well the pre-existing `--missing` option. This series avoids that route and just extends the `--missing` option for commits to solve the same problem.

V2 of the series can be found here: http://public-inbox.org/git/ZSkCGS3JPEQ71dOF@tanuki/T/#m10b562ec02834d0b222835a24a18e6ca725f99d1

Changes from v2: 

* Change the flag MISSING's bit number to avoid collision with NEEDS_BITMAP
  which was causing t5310 and t532 to fail.

Range diff from v2:

1:  a7018a319a = 1:  fa35cd21e6 revision: rename bit to `do_not_die_on_missing_objects`
2:  b186a679d4 = 2:  31074df376 rev-list: move `show_commit()` to the bottom
3:  0c8c140c27 ! 3:  d9b0d6da0c rev-list: add commit object support in `--missing` option
    @@ object.h: void object_array_init(struct object_array *array);
      /*
       * object flag allocation:
     - * revision.h:               0---------10         15             23------27
    -+ * revision.h:               0---------10         15             22------27
    ++ * revision.h:               0---------10         15             22------28
       * fetch-pack.c:             01    67
       * negotiator/default.c:       2--5
       * walker.c:                 0-2
    +@@ object.h: void object_array_init(struct object_array *array);
    +  * builtin/show-branch.c:    0-------------------------------------------26
    +  * builtin/unpack-objects.c:                                 2021
    +  */
    +-#define FLAG_BITS  28
    ++#define FLAG_BITS  29
    + 
    + #define TYPE_BITS 3
    + 
     
      ## revision.c ##
     @@ revision.c: static int process_parents(struct rev_info *revs, struct commit *commit,
    @@ revision.c: static int process_parents(struct rev_info *revs, struct commit *com
      	unsigned pass_flags;
      
     -	if (commit->object.flags & ADDED)
    -+	if (commit->object.flags & ADDED || commit->object.flags & MISSING)
    ++	if (commit->object.flags & (ADDED | MISSING))
      		return 0;
      	commit->object.flags |= ADDED;
      
    @@ revision.c: static int process_parents(struct rev_info *revs, struct commit *com
     
      ## revision.h ##
     @@
    - /* WARNING: This is also used as REACHABLE in commit-graph.c. */
    - #define PULL_MERGE	(1u<<15)
    + #define ANCESTRY_PATH	(1u<<27)
    + #define ALL_REV_FLAGS	(((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR | PULL_MERGE)
      
    -+/* WARNING: This is also used as NEEDS_BITMAP in pack-bitmap.c. */
    -+#define MISSING         (1u<<22)
    ++#define MISSING (1u<<28)
     +
    - #define TOPO_WALK_EXPLORED	(1u<<23)
    - #define TOPO_WALK_INDEGREE	(1u<<24)
    + #define DECORATE_SHORT_REFS	1
    + #define DECORATE_FULL_REFS	2
      
     
      ## t/t6022-rev-list-missing.sh (new) ##

Karthik Nayak (3):
  revision: rename bit to `do_not_die_on_missing_objects`
  rev-list: move `show_commit()` to the bottom
  rev-list: add commit object support in `--missing` option

 builtin/reflog.c            |  2 +-
 builtin/rev-list.c          | 93 +++++++++++++++++++------------------
 list-objects.c              |  4 +-
 object.h                    |  4 +-
 revision.c                  | 11 +++--
 revision.h                  | 19 ++++----
 t/t6022-rev-list-missing.sh | 74 +++++++++++++++++++++++++++++
 7 files changed, 147 insertions(+), 60 deletions(-)
 create mode 100755 t/t6022-rev-list-missing.sh