Re: [PATCH v5 22/26] t7700: consolidate code into test_no_missing_in_packs()

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 29, 2019, 21:39 UTC
Message-ID: <xmqq7e3i4b1p.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <a99a45cb6f2cc7328ef0e52fc2ea8fec537bfba9.1574884302.git.liu.denton@gmail.com>

Denton Liu <liu.denton@gmail.com> writes:

Show 10 quoted lines

> The code to test that objects were not missing from the packfile was
> duplicated many times. Extract the duplicated code into
> test_no_missing_in_packs() and use that instead.
>
> Refactor the resulting extraction so that if any git commands fail,
> their return codes are not silently lost.
>
> We were using sed to filter lines. Although not incorrect, this is
> exactly what grep is built for. Replace this invocation of sed with grep
> so that we use the correct tool for the job.

Well,

    $ sed -n -e 's/required match/desired part of the line/p'

is much much more approirate than

    $ grep -e "requred match" |
      extract desired part of the line

"grep" is better only if the original were

    $ sed -n -e '/required match/p'

but everybody would write it with grep to begin with ;-)

So, I dunno about this part of the conversion.

> Instead of verifying each file of `alt_objects/pack/*.idx` individually
> in a for-loop, batch them together into one verification step.

Do you mean this one?

	git verify-pack -v alt_objects/pack/*.idx

where we may pass 1 or more .idx file to the command? At first my reading was interrupted by a "Huh?", but that does look good. We'd need to be a bit careful to make sure that we have at least 1 .idx file, as the shell will happily feed a file whose name is "*.idx", which verify-pack would be unhappy about.

> The original testing construct was O(n^2): it used a grep in a loop to
> test whether any objects were missing in the packfile. Rewrite this to
> sort the files then use `comm -23` so that finding missing lines from
> the original file is done more efficiently.

OK. If we an show measurable speedups, it would be great, but the loop structure does look O(n^2) and unnecessary costly.

> +test_no_missing_in_packs () {
> +	myidx=$(ls -1 .git/objects/pack/*.idx) &&
> +	test_path_is_file "$myidx" &&

If there are 2 or more .idx files, or if there is none, $myidx would hopefully be a concatenation of these filenames or a string that ends with asterisk-dot-idx and would fail path_is_file. Sounds OK.

Ah, I do not have to review this part---these are repeated patterns in the original.

> +	git verify-pack -v alt_objects/pack/*.idx >orig.raw &&
> +	grep "^[0-9a-f]\{40\}" orig.raw | cut -d" " -f1 | sort >orig &&

If output from 'grep' can be used as-is, it is worth doing, but if you have to pipe it to cut, the original that used sed to filter and edit the line would probably be a better way to write it.

> +	git verify-pack -v $myidx >dest.raw &&

This part does not quote $myidx" (inherited from the original); it probably is OK, as any potentially problematic value in $myidx would have been caught as an error much earlier in this test.