[PATCH 0/8] pseudo-merge: avoid empty and non-closed pseudo-merge commits

This series fixes a couple of small issues with pseudo-merge groups, where it is possible to (a) select pseudo-merges that are not closed over reachability with respect to the bitmap's pack or MIDX, and (b) generate empty pseudo-merge commits.

The series is structured as follows:

  - The first four commits refactor the pack-bitmap machinery to make
    the bitmap_writer's packing_data structure available earlier at
    selection time, and then remove redundant arguments from the rest of
    the API as a result of that change.

  - The fifth commit makes it so we select pseudo-merges even in small
    repositories, making it easier to write tests in the remainder of
    the series.

  - The next two commits demonstrate and fix a case where we would
    generate empty pseudo-merge commits (see (b) above).

  - The final commit ensures that we do not generate pseudo-merge groups
    which reach objects not contained in the bitmap's pack or MIDX (see
    (a) above).

The bug described in (a) was noticed by Peff, and the remaining seven commits are preparatory, and/or fixing other small issues I noticed along the way while investigating the original impetus for this series.

Thanks in advance for your review!

Taylor Blau (8):
  pack-bitmap: initialize `bitmap_writer_init()` with packing_data
  pack-bitmap: drop redundant args from
    `bitmap_writer_build_type_index()`
  pack-bitmap: drop redundant args from `bitmap_writer_build()`
  pack-bitmap: drop redundant args from `bitmap_writer_finish()`
  pack-bitmap-write.c: select pseudo-merges even for small bitmaps
  t/t5333-pseudo-merge-bitmaps.sh: demonstrate empty pseudo-merge groups
  pseudo-merge.c: do not generate empty pseudo-merge commits
  pseudo-merge.c: ensure pseudo-merge groups are closed

 builtin/pack-objects.c          |  8 ++---
 midx-write.c                    | 10 +++---
 pack-bitmap-write.c             | 37 +++++++++++-----------
 pack-bitmap.h                   | 11 +++----
 pseudo-merge.c                  | 13 +++++---
 t/t5333-pseudo-merge-bitmaps.sh | 56 +++++++++++++++++++++++++++++++++
 6 files changed, 96 insertions(+), 39 deletions(-)

base-commit: 406f326d271e0bacecdb00425422c5fa3f314930