Subject: Re: [PATCH v3 7/8] rebase: update refs from 'update-ref' commands

From: Junio C Hamano <[email-masked]>
Date: Tue, 28 Jun 2022 14:15:20 -0700

"Derrick Stolee via GitGitGadget" <[email-masked]> writes:

> From: Derrick Stolee <[email-masked]>
>
> The previous change introduced the 'git rebase --update-refs' option
> which added 'update-ref <ref>' commands to the todo list of an
> interactive rebase.
>
> Teach Git to record the HEAD position when reaching these 'update-ref'
> commands. The ref/OID pair is stored in the
> $GIT_DIR/rebase-merge/update-refs file. A previous change parsed this
> file to avoid having other processes updating the refs in that file
> while the rebase is in progress.
>
> Not only do we update the file when the sequencer reaches these
> 'update-ref' commands, we then update the refs themselves at the end of
> the rebase sequence. If the rebase is aborted before this final step,
> then the refs are not updated.

So, in general, we would

 * first scan the range of commits being rebased
 * compute what should happen and write the "todo" thing
 * write also "update-refs" to lick the branches to repel others
 * execute the "todo" insns one by one, possibly giving control back

And this order is important---update-refs file is written fairly
early, and the branches potentially involved in the rebase are all
protected during the time-consuming (due to possibility of manual
conflict resolution) execution step.

Makes sense.

> diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
> index 3cd20733bc8..63a69bc073e 100755
> --- a/t/t3404-rebase-interactive.sh
> +++ b/t/t3404-rebase-interactive.sh
> @@ -1813,6 +1813,29 @@ test_expect_success '--update-refs adds commands with --rebase-merges' '
>  	)
>  '
>  
> +compare_two_refs () {
> +	git rev-parse $1 >expect &&
> +	git rev-parse $2 >actual &&
> +	test_cmp expect actual
> +}
> +
> +test_expect_success '--update-refs updates refs correctly' '
> +	git checkout -B update-refs no-conflict-branch &&
> +	git branch -f base HEAD~4 &&
> +	git branch -f first HEAD~3 &&
> +	git branch -f second HEAD~3 &&
> +	git branch -f third HEAD~1 &&
> +	test_commit extra2 fileX &&
> +	git commit --amend --fixup=L &&
> +
> +	git rebase -i --autosquash --update-refs primary &&
> +
> +	compare_two_refs HEAD~3 refs/heads/first &&
> +	compare_two_refs HEAD~3 refs/heads/second &&
> +	compare_two_refs HEAD~1 refs/heads/third &&
> +	compare_two_refs HEAD refs/heads/no-conflict-branch
> +'
> +
>  # This must be the last test in this file
>  test_expect_success '$EDITOR and friends are unchanged' '
>  	test_editor_unchanged

It would be nice to also have a test that makes sure that other
people will be prevented from checking out a branch whose tips may
be updated at the end.

Thanks.