Subject: Re: [PATCH 1/2] gc: add tests for --cruft and friends

From: Junio C Hamano <[email-masked]>
Date: Wed, 03 Aug 2022 14:56:04 -0700

Emily Shaffer <[email-masked]> writes:

> In 5b92477f89 (builtin/gc.c: conditionally avoid pruning objects via
> loose, 2022-05-20) gc learned to respect '--cruft' and 'gc.cruftPacks'.
> '--cruft' is exercised in t5329-pack-objects-cruft.sh, but in a way that
> doesn't check whether a lone gc run generates these cruft packs.
> 'gc.cruftPacks' is never exercised.
>
> Add some tests to exercise these options to gc in the gc test suite.
>
> Signed-off-by: Emily Shaffer <[email-masked]>
> ---
>  t/t6500-gc.sh | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>
> diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
> index cd6c53360d..e4c2c3583d 100755
> --- a/t/t6500-gc.sh
> +++ b/t/t6500-gc.sh
> @@ -202,6 +202,42 @@ test_expect_success 'one of gc.reflogExpire{Unreachable,}=never does not skip "e
>  	grep -E "^trace: (built-in|exec|run_command): git reflog expire --" trace.out
>  '
>  
> +test_expect_success 'gc --cruft generates a cruft pack' '
> +	git init crufts &&
> +	test_when_finished "rm -fr crufts" &&
> +	(
> +		cd crufts &&
> +		test_commit base &&
> +
> +		test_commit --no-tag foo &&
> +		test_commit --no-tag bar &&
> +		git reset HEAD^^ &&
> +
> +		git gc --cruft &&
> +
> +		cruft=$(basename $(ls .git/objects/pack/pack-*.mtimes) .mtimes) &&

What guarantees that we will have one pack-*.mtimes?  

I do not mind if we reliably diagnosed it as an error when "git gc
--cruft" created two cruft packs, but I do mind if this call to
basename receives two files plus .mtimes suffix and misbehaves.

Is the fact that it is accompanied by a .mtimes file the only clue
that a pack is a "cruft" pack?  Given that the usefulness of mtimes
based expiration approach is doubted, do we want to rely on it (and
having to redesign the test)?

I think the right test would be to

 * make a list of all "in use" objects;

 * see if there is one (or more) packfile that does not contain any
   "in use" objects (look at their .idx file).

If all packfiles are packs with objects that are still in use, then
we did not create a cruft pack.

> +		test_path_is_file .git/objects/pack/$cruft.pack

DQuote the whole thing, i.e.

		test_path_is_file ".git/objects/pack/$cruft.pack"