Subject: Re: [PATCH] refs: allow @{n} to work with n-sized reflog

From: SZEDER Gábor <[email-masked]>
Date: Tue, 5 Jan 2021 09:52:21 +0100

On Fri, Jan 01, 2021 at 05:36:06PM -0800, Denton Liu wrote:
> This sequence works
> 
> 	$ git checkout -b newbranch
> 	$ git commit --allow-empty -m one
> 	$ git show -s newbranch@{1}
> 
> and shows the state that was immediately after the newbranch was
> created.
> 
> But then if you do
> 
> 	$ git reflog expire --expire=now refs/heads/newbranch
> 	$ git commit --allow=empty -m two
> 	$ git show -s newbranch@{1}
> 
> you'd be scolded with
> 
> 	fatal: log for 'newbranch' only has 1 entries
> 
> While it is true that it has only 1 entry, we have enough
> information in that single entry that records the transition between
> the state in which the tip of the branch was pointing at commit
> 'one' to the new commit 'two' built on it, so we should be able to
> answer "what object newbranch was pointing at?". But we refuse to
> do so.

Great!  I've run into this issue quite a while ago with regular 'git
gc' expiring too old reflog entries, and wondered while the @{N}
notation errored out while the information was clearly still there in
the reflog.

https://public-inbox.org/git/20130619125059.GD20052@goldbirke/T/#u

> @@ -139,6 +139,19 @@ test_expect_success 'master@{n} for various n' '
>  	test_must_fail git rev-parse --verify master@{$Np1}
>  '
>  
> +test_expect_success '@{1} works with only one reflog entry' '
> +	git checkout -B newbranch &&
> +	git reflog expire --expire=now refs/heads/newbranch &&
> +	git commit --allow-empty -mexpired &&
> +	git rev-parse --verify newbranch@{1}
> +'
> +
> +test_expect_success '@{0} works with empty reflog' '
> +	git checkout -B newbranch &&
> +	git reflog expire --expire=now refs/heads/newbranch &&
> +	git rev-parse --verify newbranch@{0}
> +'

I agree with Martin about these tests: not failing is one thing, but
we should make sure that the right value is printed.

>  test_expect_success SYMLINKS 'ref resolution not confused by broken symlinks' '
>  	ln -s does-not-exist .git/refs/heads/broken &&
>  	test_must_fail git rev-parse --verify broken
> -- 
> 2.30.0
>