Re: [PATCH 3/8] t34xx: don't expire reflogs where it matters

[Justin Tobler <jltobler@gmail.com>]

On 26/02/20 11:15AM, Patrick Steinhardt wrote:
> We have a couple of tests in the t34xx range that rely on reflogs. This
> never really used to be a problem, but in a subsequent commit we will
> change the default maintenance strategy from "gc" to "geometric", and
> this will cause us to drop all reflogs in these tests.
> 
> This may seem surprising and like a bug at first, but it's actually not.
> The main difference between these two strategies is that the "gc"
> strategy will skip all maintenance in case the object database is in a
> well-optimized state. The "geometric" strategy has separate subtasks
> though, and the conditions for each of these tasks is evaluated on a
> case by case basis. This means that even if the object database is in
> good shape, we may still decide to expire reflogs.
> 
> So why is that a problem? The issue is that Git's test suite hardcodes
> the committer and author dates to a date in 2005. Interestingly though,
> these hardcoded dates not only impact the commits, but also the reflog
> entries. The consequence is that all newly written reflog entries are
> immediately considered stale as our reflog expiration threshold is in
> the range of weeks, only. It follows that executing `git reflog expire`
> will thus immediately purge all reflog entries.
> 
> This hasn't been a problem in our test suite by pure chance, as the
> repository shapes simply didn't cause us to perform actual garbage
> collection. But with the upcoming "geometric" strategy we _will_ start
> to execute `git reflog expire`, thus surfacing this issue.

Interesting find.

> Prepare for this by explicitly disabling reflog expiration in tests
> impacted by this upcoming change.

Makes sense.

> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  t/t3404-rebase-interactive.sh  | 2 ++
>  t/t3406-rebase-message.sh      | 3 +++
>  t/t3431-rebase-fork-point.sh   | 2 ++
>  t/t3432-rebase-fast-forward.sh | 2 ++
>  4 files changed, 9 insertions(+)
> 
> diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
> index e778dd8ae4..5e4623f7f1 100755
> --- a/t/t3404-rebase-interactive.sh
> +++ b/t/t3404-rebase-interactive.sh
> @@ -31,6 +31,8 @@ Initial setup:
>  . "$TEST_DIRECTORY"/lib-rebase.sh
>  
>  test_expect_success 'setup' '
> +	git config set gc.reflogExpire never &&
> +	git config set gc.reflogExpireUnreachable never &&

As it may not be immediately obvious, it could be helpful for future
readers to explain in a comment that reflog dates are hardcoded to a
date that would be immediately expired and thus the need for this
configuration.

This patch looks good to me.

-Justin