[PATCH 0/8] pack-bitmap: fix various pseudo-merge bugs

[Taylor Blau <me@ttaylorr.com>]

This series fixes several bugs in the pseudo-merge bitmap implementation
that caused the pseudo-merge application path to be effectively broken
during fill-in traversal.

Peff noticed that this code path was never triggered by the existing
test suite, and investigating that observation uncovered a handful of
bugs, some compounding.

The first two patches introduce test infrastructure: a 'bitmap write'
test helper that gives tests precise control over which commits receive
individual bitmaps, and a set of "test_expect_failure" tests
demonstrating each bug.

The next four patches fix the bugs in the per-commit pseudo-merge
lookup:

  - The pseudo-merge commit lookup table was sorted by OID rather than
    by bit position, causing the reader's binary search to fail.

  - The binary search in pseudo_merge_at() had its lo/hi updates
    swapped.

  - The extended pseudo-merge lookup path had three compounding bugs: a
    wrong entry-size calculation in the writer, a misinterpretation of
    extended table entries in the reader, and a silently-swallowed error
    check.

The final two patches fix issues in pseudo-merge group selection:

  - find_pseudo_merge_group_for_ref() did not parse commits before
    inspecting their dates, so all candidates had date == 0 and were
    unconditionally placed in the "stable" bucket.

  - The config validation for bitmapPseudoMerge.*.sampleRate accepted 0,
    which leads to a division by zero once the date classification is
    fixed and the unstable code path is exercised.

There is also a small fix for a regex leak when the pattern key is
overridden in config.

Thanks in advance for your review!

Taylor Blau (8):
  t/helper: add 'test-tool bitmap write' subcommand
  t5333: demonstrate various pseudo-merge bugs
  pack-bitmap-write: sort pseudo-merge commit lookup table in pack order
  pack-bitmap: fix inverted binary search in `pseudo_merge_at()`
  pack-bitmap: fix pseudo-merge lookup for shared commits
  pack-bitmap: parse commits in `find_pseudo_merge_group_for_ref()`
  pack-bitmap: reject pseudo-merge "sampleRate" of 0
  pack-bitmap: prevent pattern leak on pseudo-merge re-assignment

 pack-bitmap-write.c             |  23 +++-
 pseudo-merge.c                  |  19 ++-
 t/helper/test-bitmap.c          | 110 ++++++++++++++-
 t/t5310-pack-bitmaps.sh         |  24 ++++
 t/t5333-pseudo-merge-bitmaps.sh | 230 ++++++++++++++++++++++++++++++++
 5 files changed, 396 insertions(+), 10 deletions(-)


base-commit: 8c9303b1ffae5b745d1b0a1f98330cf7944d8db0
-- 
2.54.0.rc1.73.g8f4e0170952