Re: [PATCH] sparse-index: copy dir_hash in ensure_full_index()

> From: Jeff Hostetler <jeffhost@microsoft.com>
> 
> Copy the 'index_state->dir_hash' back to the real istate after expanding
> a sparse index.
> 
> A crash was observed in 'git status' during some hashmap lookups with
> corrupted hashmap entries.  During an index expansion, new cache-entries
> are added to the 'index_state->name_hash' and the 'dir_hash' in a
> temporary 'index_state' variable 'full'.  However, only the 'name_hash'
> hashmap from this temp variable was copied back into the real 'istate'
> variable.  The original copy of the 'dir_hash' was incorrectly
> preserved.  If the table in the 'full->dir_hash' hashmap were realloced,
> the stale version (in 'istate') would be corrupted.
> 
> The test suite does not operate on index sizes sufficiently large to
> trigger this reallocation, so they do not cover this behavior.
> Increasing the test suite to cover such scale is fragile and likely
> wasteful.
> 
> Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>     sparse-index: copy dir_hash in ensure_full_index()
>     
>     This fix is an issue we discovered in our first experimental release of
>     the sparse index in the microsoft/git fork. We fixed it in the latest
>     experimental release [1] and then I almost forgot about it until we
>     started rebasing sparse-index work on top of the 2.33.0 release
>     candidates.
>     
>     [1] https://github.com/microsoft/git/releases/tag/v2.32.0.vfs.0.102.exp
>     
>     This is a change that can be taken anywhere since 4300f8 (sparse-index:
>     implement ensure_full_index(), 2021-03-30), but this version is based on
>     v2.33.0-rc2.