[PATCH 0/3] delta-island fixes

This fixes a few bugs in the cc/delta-islands topic: one major, and two minor.

Sadly, the major one was not caught by our test suite, and I'm not sure how to remedy that. The problem is a memory management one, and happens only when you have a reasonably large number of objects. So it triggers readily when run on a real repository, but not on the toy one in t5320. Creating a much larger repository there would make the test suite more expensive.

In cases like this I think it's often a good idea to have a perf test. Those are expensive anyway, and we'd have the double benefit of exercising the code and showing off the performance improvement. But the delta-island code only makes sense on a very specialized repo: one where you have multiple related but diverging histories. You could simulate that by picking two branches in a repository, but the effect is going to be miniscule.

Anyway, here are the fixes without tests. We should at least apply these before v2.20 ships with the bugs.

  [1/3]: pack-objects: fix tree_depth and layer invariants
  [2/3]: pack-objects: zero-initialize tree_depth/layer arrays
  [3/3]: pack-objects: fix off-by-one in delta-island tree-depth computation

 builtin/pack-objects.c | 4 +++-
 git-compat-util.h      | 1 +
 pack-objects.h         | 4 ++--
 3 files changed, 6 insertions(+), 3 deletions(-)