Subject: Re: [PATCH v6 1/2] t1092: add tests for `git diff-files`

From: Victoria Dye <[email-masked]>
Date: Tue, 21 Mar 2023 15:19:29 -0700

Junio C Hamano wrote:
> Victoria Dye <[email-masked]> writes:
> 
>> The strange thing is, once I fixed the 'mkdir' issue in my local copy of
>> these patches, these 'test_all_match diff-files' calls succeeded. It turns
>> out that 'git diff-files' in the 'full-checkout', like in 'sparse-checkout',
>> reports a difference in 'folder1/a' that doesn't actually exist. So the bug
>> isn't in sparse-checkout as I initially assumed [1], but rather in
>> diff-files itself.
> 
> Is that a bug, or just a common "ah, you forgot to refresh the index"?

Ah, you're right - I completely forgot about 'diff-files' not refreshing the
index (since 'diff', by default, does). The ctime is (often, but not always)
different on the copied file than what's in the index, so 'diff-files' shows
the file as "modified" if the index isn't refreshed. 

Going back to these tests, the goal is to make sure that 'diff-files' finds
the correct index entry (possibly in a sparse directory) and compares that
correctly to what's on disk. But since we want to ignore ctime differences,
we could use '--stat' (or '-p', or '--num-stat':

	run_on_all mkdir -p folder1 &&
	run_on_all cp a folder1/a &&

	# file present on-disk without modifications
	# use `--stat` to ignore file creation time differences in
	# unrefreshed index
	test_all_match git diff-files --stat &&
	test_all_match git diff-files --stat folder1/a &&

I don't think that makes the test any less comprehensive (especially since
later on in the same test, we modify the contents of 'folder1/a' and get the
expected "modified" status in 'git diff-files' without '--stat'), but it
avoids potential breakages related to inconsistency in file creation time.