Re: [RFC][PATCH v1] write-tree: integrate with sparse index

> Update 'git write-tree' to allow using the sparse-index in memory
> without expanding to a full one.
>
> The recursive algorithm for update_one() was already updated in 2de37c5
> (cache-tree: integrate with sparse directory entries, 2021-03-03) to
> handle sparse directory entries in the index. Hence we can just set the
> requires-full-index to false for "write-tree".
>
> The `p2000` tests demonstrate a ~96% execution time reduction for 'git
> write-tree' using a sparse index:
>
> Test                                           before  after
> -----------------------------------------------------------------
> 2000.78: git write-tree (full-v3)              0.34    0.33 -2.9%
> 2000.79: git write-tree (full-v4)              0.32    0.30 -6.3%
> 2000.80: git write-tree (sparse-v3)            0.47    0.02 -95.8%
> 2000.81: git write-tree (sparse-v4)            0.45    0.02 -95.6%
>
> Signed-off-by: Shuqi Liang <cheskaqiqi@gmail.com>
> ---
>  builtin/write-tree.c                     |  4 ++++
>  t/perf/p2000-sparse-operations.sh        |  1 +
>  t/t1092-sparse-checkout-compatibility.sh | 28 ++++++++++++++++++++++++
>  3 files changed, 33 insertions(+)