Re: [PATCH 2/3] t3404: rebase: interactive: demonstrate short SHA-1 collision

> The 'todo' sheet for interactive rebase shows abbreviated SHA-1's and
> then performs its operations upon those shortened values. This can lead
> to an abort if the SHA-1 of a reworded or edited commit is no longer
> unique within the abbreviated SHA-1 space and a subsequent SHA-1 in the
> todo list has the same abbreviated value.
>
> For example:
>
>   edit f00dfad first
>   pick badbeef second
>
> If, after editing, the new SHA-1 of "first" is now
> badbeef5ba78983324dff5265c80c4490d5a809a, then the subsequent 'pick
> badbeef second' will fail since badbeef is no longer a unique SHA-1
> abbreviation:
>
>   error: short SHA1 badbeef is ambiguous.
>   fatal: Needed a single revision
>   Invalid commit name: badbeef
>
> Demonstrate this problem with a couple of specially crafted commits
> which initially have distinct abbreviated SHA-1's, but for which the
> abbreviated SHA-1's collide after a simple rewording of the first
> commit's message.
>
> Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
> ---
>  t/t3404-rebase-interactive.sh | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
> index af141be..e5ebec6 100755
> --- a/t/t3404-rebase-interactive.sh
> +++ b/t/t3404-rebase-interactive.sh
> @@ -977,4 +977,21 @@ test_expect_success 'rebase -i with --strategy and -X' '
>  	test $(cat file1) = Z
>  '
>  
> +test_expect_success 'short SHA-1 setup' '
> +	test_when_finished "git checkout master" &&
> +	git checkout --orphan collide &&
> +	git rm -rf . &&
> +	unset test_tick &&

> +	test_commit collide1 collide &&
> +	test_commit --notick collide2 collide &&
> +	test_commit --notick "collide3 115158b5" collide collide3 collide3
> +'
>
> +test_expect_failure 'short SHA-1 collide' '
> +	test_when_finished "reset_rebase && git checkout master" &&
> +	git checkout collide &&
> +	FAKE_COMMIT_MESSAGE="collide2 815200e" \