Re: rebase -i --update-refs can lead to deletion of branches

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Victoria

On 04/11/2022 00:31, Victoria Dye wrote:
> herr.kaste wrote:
>> Now, I should just have not used `--update-refs` in the first place but anyway
>> I decide late that I rather don't want to update "master" etc. and it should
>> probably not delete the local refs.
>>
> 
> Agreed, this doesn't seem like desired behavior - the opposite of "update
> the ref" isn't "delete the ref". ;)
> 
> The reason it's happening is because, when '--update-refs' is used, the
> rebase starts by constructing a list of 'update_ref_record's for each of the
> refs that *could* be updated. Each item in that list contains the
> corresponding ref's "before" commit OID (i.e., what it currently points to)
> and initializes the "after" OID to null. When an 'update-ref' line is
> encountered in the 'rebase-todo', the "after" OID is updated with the
> newly-rebased value. However, if an 'update-ref' line is removed from the
> 'rebase-todo', the "after" value is never updated. Then, when the rebase
> finishes and the ref state data is applied, all of the entries with null
> "after" OIDs are deleted.
> 
> The three options for a fix I can think of are:
> 
>    1. initialize the "after" OID to the value of "before".
>    2. don't update refs with a null "after" OID.
>    3. initialize the "after" OID to the value of "before", don't update the
>       ref if "before" == "after".
> 
> I think #3 is the best option, since it avoids the unnecessary updates of #1
> and leaves a cleaner path to a 'delete-ref' option (like the one proposed
> elsewhere in the thread [1]) than #2. I'll send a patch shortly.

We should be removing the entry entirely if the user removes it from the 
todo-list see b3b1a21d1a (sequencer: rewrite update-refs as user edits 
todo list, 2022-07-19) where the commit message says

1. If a '<ref>/<before>/<after>' triple in the update-refs file does not
    have a matching 'update-ref <ref>' command in the todo-list _and_ the
    <after> value is the null OID, then remove that triple. Here, the
    user removed the 'update-ref <ref>' command before it was executed,
    since if it was executed then the <after> value would store the
    commit at that position.

I think that is the best approach but it seems the implementation isn't 
actually doing that.

Best Wishes

Phillip



> [1] https://lore.kernel.org/git/CA+JQ7M-GbBTHZZ9xOLR=FitWFpUnkfuep9kSfNPxuSbJbKteGw@mail.gmail.com/
> 
> Thanks for reporting!
> - Victoria
>