Shaoxuan Yuan wrote:

Integrate `git-grep` with sparse-index and test the performance
improvement.

Changes since v5
----------------

* Drop the `--sparse` option patch and edit corresponding tests. 
  We can wait until a better name is decided to replace `--sparse`.

* Modify the commit message, especially get rid of the `--sparse`
  occurences.

Thanks for the update! Everything in this patch is either part of the
previous version's patch 3 or comes from the tests & sparse index enabling
of the previous patch 2. The resulting patch enables the sparse index for
all usage of '--cached', and avoids any user option changes. 

All that to say, this version looks good to me!

Thanks!
- Victoria