[PATCH 0/3] Integrate the sparse index with 'git apply' and 'git add -p/-i'

The sparse index helps make some Git commands faster when using sparse-checkout in cone mode. However, not all code paths are aware that the index can have non-blob entries, so we are careful about rolling this feature out gradually. The cost of this rollout is that some commands are slower with the sparse index as they need to expand a sparse index into a full index in memory, which requires parsing tree objects to construct the full path list.

This patch series focuses on the 'git add -p' command, which is slow with the sparse index for a couple of reasons, handled in the first two patches:

 1. 'git add -p' uses 'git apply' as a subcommand and 'git apply' needs
    integration with the sparse index. Luckily, we just need to add the repo
    setting and appropriate tests to confirm it behaves as expected.
 2. The interactive modes of 'git add' ('-p' and '-i') leave cmd_add()
    before the code that sets the repo setting to allow for a sparse index.
    Patch 2 fixes this and adds appropriate tests to confirm the behavior in
    a sparse-checkout.

A third patch adds a performance test to p2000-sparse-operations.sh to confirm that we are getting the performance improvement we expect:

                        BASE    PATCH 1        PATCH 2
---------------------------------------------------------
2000.118: (full-v3)     0.80   0.84 +5.0%     0.84  +5.0%
2000.119: (full-v4)     0.76   0.79 +3.9%     0.80  +5.3%
2000.120: (sparse-v3)   2.09   1.39 -33.5%    0.07 -96.7%
2000.121: (sparse-v4)   2.09   1.39 -33.5%    0.07 -96.7%

Thanks, -Stolee

Derrick Stolee (3):
  apply: integrate with the sparse index
  git add: make -p/-i aware of sparse index
  p2000: add performance test for 'git add -p'

 builtin/add.c                            |   7 +-
 builtin/apply.c                          |   7 +-
 t/perf/p2000-sparse-operations.sh        |   1 +
 t/t1092-sparse-checkout-compatibility.sh | 102 +++++++++++++++++++++++
 4 files changed, 113 insertions(+), 4 deletions(-)

base-commit: 6c0bd1fc70efaf053abe4e57c976afdc72d15377
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1914%2Fderrickstolee%2Fapply-sparse-index-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1914/derrickstolee/apply-sparse-index-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1914