Re: [PATCH v2 2/3] update-index: add --show-index-version

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 12, 2023, 19:01 UTC
Message-ID: <xmqqbke7nrlz.fsf@gitster.g>
In-Reply-To: <owlybke8kkcf.fsf@fine.c.googlers.com>

Linus Arver <linusa@google.com> writes:

Show 5 quoted lines

> Junio C Hamano <gitster@pobox.com> writes:
>
>> "git update-index --version N" is used to set the index format
>
> s/--version/--index-version

Good eyes.

Show 5 quoted lines

>> +	`git add -N`.  With `--verbose` option, also reports the
>
> How about
>
>     `git add -N`.  With `--verbose`, also report the

Yup, that is much better.

Show 8 quoted lines

>>  		OPT_INTEGER(0, "index-version", &preferred_index_format,
>>  			N_("write index in this format")),
>> +		OPT_SET_INT(0, "show-index-version", &preferred_index_format,
>> +			    N_("show index format version"), -1),
>
> How about
>
>     "show on-disk index format version"

OK. The entry before that says "write" and it makes it clear enough that it is talking about the "on-disk" thing, hence "write index" is sufficient. The readers, who do not know the "format version" matters only on-disk and does not matter once the index data gets slurped into memory, would benefit with "on-disk index" here. I will also take your "show" -> "report" suggestion.

Show 18 quoted lines

>> diff --git a/t/t2107-update-index-basic.sh b/t/t2107-update-index-basic.sh
>> index 89b285fa3a..c78d1e9396 100755
>> --- a/t/t2107-update-index-basic.sh
>> +++ b/t/t2107-update-index-basic.sh
>> @@ -111,4 +111,20 @@ test_expect_success '--chmod=+x and chmod=-x in the same argument list' '
>>  	test_cmp expect actual
>>  '
>>
>> +test_expect_success '--index-version' '
>> +	git commit --allow-empty -m snap &&
>> +	git reset --hard &&
>
> Not sure why this "git reset --hard" is needed here --- is it to clear
> out state from previous test cases? If so, perhaps it's better to run
> this as the very first command in this test case?
>
> But this also makes me wonder why "git commit --allow-empty -m snap" is
> even necessary (if we already have a git repo)?

There is no commit yet in this repository at this point, which means that "reset --hard [HEAD]" cannot be the first command. There are newly added paths in the index, some of which are further modified in the working tree. Creating a snapshot commit will record what is in the index, and a hard reset will make the contents of the working tree match exactly what was in the index, reverting the modification made to some paths in the working tree.

Having said that, we may further want to tighten these "clean the slate" steps for later tests (read on).

Show 6 quoted lines

>> +	git update-index --index-version 2 >actual &&
>> +	test_must_be_empty actual &&
>
> Before we do "--index-version 2", it may be desirable to run the
> "--show-index-version" flag first to see what we have before modifying
> it with "2".

That was what I specifically wanted to avoid. I am not interested in testing what the default version of the day is. The only thing this invocation cares about is to (try to) use the version 2; it will be detected as a failure if the next show-index-version reported something else ...

>> +	git update-index --show-index-version >actual &&
>> +	echo 2 >expect &&
>> +	test_cmp expect actual &&

... which is checked here.

>> +	git update-index --index-version 4 --verbose >actual &&
>> +	echo "index-version: was 2, set to 4" >expect &&
>> +	test_cmp expect actual

And how a transition is reported with --verbose is tested here.

Show 15 quoted lines

>> +'
>
> How about adding this check below to check what happens if the newly-set
> version is the same as the existing version?
>
>         git update-index --index-version 4 --verbose >actual &&
>         echo "index-version: was 4, set to 4" >expect &&
>         test_cmp expect actual
>
> And also how about a similar check, but for downgrading from a higher
> version number to a lower one?
>
>         git update-index --index-version 2 --verbose >actual &&
>         echo "index-version: was 4, set to 2" >expect &&
>         test_cmp expect actual

I assumed that the flipping between versions without --verbose had adequate coverage and the tests this patch adds were solely about reporting with the "--verbose" option. It seems there is no such test coverage, so these may want to be added. Perhaps we should flip from 2 to 4 _without_ verbose and make sure we are still silent as well.

Testing downgrading an index with unspecified [*] contents from 3 (or higher) to 2 would be unwise, as such a conversion may or may not work depending on the contents. I will tighten the "clean the slate" steps and add downgrades to the list, as the initial "try to set to 2" may not even work with unknown contents in the index.

Thanks.

[Footnote]

* This is in a very late part of the test script and the state
  previous tests left us will change over time.