Re: [PATCH 2/7] sparse-index: update command for expand/collapse test

From: Victoria Dye <vdye@github.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Taylor Blau <me@ttaylorr.com>,
	Victoria Dye via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org, stolee@gmail.com, newren@gmail.com
Subject: Re: [PATCH 2/7] sparse-index: update command for expand/collapse test
Date: Thu, 30 Sep 2021 18:59:57 -0400	[thread overview]
Message-ID: <e6049a17-c721-c596-51a6-101cb6065829@github.com> (raw)
In-Reply-To: <xmqqk0ixagw8.fsf@gitster.g>

Junio C Hamano wrote:
> Victoria Dye <vdye@github.com> writes:
> 
>> Taylor Blau wrote:
>>> On Thu, Sep 30, 2021 at 02:50:56PM +0000, Victoria Dye via GitGitGadget wrote:
>>>> From: Victoria Dye <vdye@github.com>
>>>>
>>>> In anticipation of multiple commands being fully integrated with sparse
>>>> index, update the test for index expand and collapse for non-sparse index
>>>> integrated commands to use `mv`.
>>>> ...
>>>>  	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
>>>> -		git -C sparse-index -c core.fsmonitor="" reset --hard &&
>>>> +		git -C sparse-index -c core.fsmonitor="" mv a b &&
>>>
>>> Double-checking my understanding as somebody who is not so familiar with
>>> t1092: this test is to ensure that commands which don't yet understand
>>> the sparse index can temporarily expand it in order to do their work?
>>
>> Exactly - if a command doesn't explicitly enable use of the sparse index by
>> setting `command_requires_full_index` to 0, the index is expanded if/when it
>> is first read during the command's execution and collapsed if/when it is
>> written to disk. This test makes sure that mechanism works as intended.
> 
> Sorry, I do not quite follow.  
> 
> So is this "before this series of patches, 'reset --hard' can be
> used to as a sample of a command that expands and then collapses,
> but because it no longer is a good sample of a command so we replace
> it with 'mv a b'"?

Yes, because this series enables sparse index integration in `git reset`,
the test no longer applies to that command (but it does apply to `git mv`).

> Do we need to update this further when "mv a b"
> learns to expand and then collapse?

Unfortunately, yes. `git mv` was picked more-or-less at random from the set
of commands that read the index and don't already have sparse index
integrations (excluding those I know are planned for sparse index
integration in the near future). If `git mv` were to be updated to disable
`command_requires_full_index`, the command in the test would need to change
again.

For what it's worth, I do think the test itself is valuable, since it makes
sure a command's capability to use the sparse index is always the result of
an intentional update to (and review of) the code.