Re: [PATCH 8/9] update-index: integrate with sparse index

[Victoria Dye <vdye@github.com>]

Elijah Newren wrote:
> On Tue, Jan 4, 2022 at 9:37 AM Victoria Dye via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
>>
>> From: Victoria Dye <vdye@github.com>
>>
>> Enable usage of the sparse index with `update-index`. Most variations of
>> `update-index` work without explicitly expanding the index or making any
>> other updates in or outside of `update-index.c`.
>>
>> The one usage requiring additional changes is `--cacheinfo`; if a file
>> inside a sparse directory was specified, the index would not be expanded
>> until after the cache tree is invalidated, leading to a mismatch between the
>> index and cache tree. This scenario is handled by rearranging
>> `add_index_entry_with_check`, allowing `index_name_stage_pos` to expand the
>> index *before* attempting to invalidate the relevant cache tree path,
>> avoiding cache tree/index corruption.
>>
>> Signed-off-by: Victoria Dye <vdye@github.com>
>> ---
>>  builtin/update-index.c                   |  3 +++
>>  read-cache.c                             | 10 +++++++---
>>  t/t1092-sparse-checkout-compatibility.sh | 12 ++++++++++++
>>  3 files changed, 22 insertions(+), 3 deletions(-)
>>
>> diff --git a/builtin/update-index.c b/builtin/update-index.c
>> index 187203e8bb5..605cc693bbd 100644
>> --- a/builtin/update-index.c
>> +++ b/builtin/update-index.c
>> @@ -1077,6 +1077,9 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
>>
>>         git_config(git_default_config, NULL);
>>
>> +       prepare_repo_settings(r);
>> +       the_repository->settings.command_requires_full_index = 0;
>> +
>>         /* we will diagnose later if it turns out that we need to update it */
>>         newfd = hold_locked_index(&lock_file, 0);
>>         if (newfd < 0)
>> diff --git a/read-cache.c b/read-cache.c
>> index cbe73f14e5e..b4600e954b6 100644
>> --- a/read-cache.c
>> +++ b/read-cache.c
>> @@ -1339,9 +1339,6 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
>>         int skip_df_check = option & ADD_CACHE_SKIP_DFCHECK;
>>         int new_only = option & ADD_CACHE_NEW_ONLY;
>>
>> -       if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
>> -               cache_tree_invalidate_path(istate, ce->name);
>> -
>>         /*
>>          * If this entry's path sorts after the last entry in the index,
>>          * we can avoid searching for it.
>> @@ -1352,6 +1349,13 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
>>         else
>>                 pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce), EXPAND_SPARSE);
>>
>> +       /*
>> +        * Cache tree path should be invalidated only after index_name_stage_pos,
>> +        * in case it expands a sparse index.
>> +        */
>> +       if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
>> +               cache_tree_invalidate_path(istate, ce->name);
>> +
>>         /* existing match? Just replace it. */
>>         if (pos >= 0) {
>>                 if (!new_only)
>> diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
>> index 6804ab23a27..bc0741c970d 100755
>> --- a/t/t1092-sparse-checkout-compatibility.sh
>> +++ b/t/t1092-sparse-checkout-compatibility.sh
>> @@ -1216,6 +1216,18 @@ test_expect_success 'sparse index is not expanded: blame' '
>>         done
>>  '
>>
>> +test_expect_success 'sparse index is not expanded: update-index' '
>> +       init_repos &&
>> +
>> +       echo "test" >sparse-index/README.md &&
>> +       echo "test2" >sparse-index/a &&
>> +       rm -f sparse-index/deep/a &&
>> +
>> +       ensure_not_expanded update-index --add README.md &&
>> +       ensure_not_expanded update-index a &&
>> +       ensure_not_expanded update-index --remove deep/a
>> +'
> 
> The commit message said this change was about --cacheinfo, but this
> test doesn't use that option.  I'm confused; was this a bad patch
> splitting by chance?
> 

It was not - the commit message title is "update-index: integrate with
sparse index" and the message starts by saying that this patch enables use
of the sparse index for *all* of `update-index` (where "[m]ost variations of
`update-index` work without...making any other updates in or outside of
`update-index.c`").

It goes on to say that the `--cache-info` option is an exception to the
above statement (that most variations work without updates outside
`update-index.c`) because it requires a slight change to
`add_index_entry_with_check(...)` to avoid index corruption. That change is
also in this patch, but it's not the main "focus".

The test added here is intended to broadly test `update-index` with a sparse
index. I'll add a case for `--cacheinfo` in my next re-roll but, for
context, the reason I didn't originally is because I focused on the (as far
as I could tell) most commonly-used variations of `update-index`.

>> +
>>  # NEEDSWORK: a sparse-checkout behaves differently from a full checkout
>>  # in this scenario, but it shouldn't.
>>  test_expect_success 'reset mixed and checkout orphan' '
>> --
>> gitgitgadget
>>