Annoyance wrt ref@{1} and reflog expiry

> I have been disturbed by this for a long time, but not strongly
> enough to do anything to it.
>
> 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.  
>
> And it is unintuitive.  It is understandable to the users that all
> the ref history before "reflog expire" is lost---it was what the end
> user asked Git to do.  But after creating one commit on the state
> (or do anything else that moves the ref) and finding it regrettable,
> "git reset --hard @{1}" should be a viable way to recover from the
> mistake made _after_ the reflog entries were expired.
>
> Opinions?

>> But then if you do
>>
>>     $ git reflog expire --expire=now refs/heads/newbranch
>>     $ git commit --allow=empty -m two
>>     $ git show -s newbranch@{1}
>> ...
>> And it is unintuitive.  It is understandable to the users that all
>> the ref history before "reflog expire" is lost---it was what the end
>> user asked Git to do.  But after creating one commit on the state
>> (or do anything else that moves the ref) and finding it regrettable,
>> "git reset --hard @{1}" should be a viable way to recover from the
>> mistake made _after_ the reflog entries were expired.

> Sergey Organov <sorganov@gmail.com> writes:
> 
> >> But then if you do
> >>
> >>     $ git reflog expire --expire=now refs/heads/newbranch
> >>     $ git commit --allow=empty -m two
> >>     $ git show -s newbranch@{1}
> >> ...
> >> And it is unintuitive.  It is understandable to the users that all
> >> the ref history before "reflog expire" is lost---it was what the end
> >> user asked Git to do.  But after creating one commit on the state
> >> (or do anything else that moves the ref) and finding it regrettable,
> >> "git reset --hard @{1}" should be a viable way to recover from the
> >> mistake made _after_ the reflog entries were expired.
> 
> And the expiration does not have to be --expire=now; what happens
> more often is when I expire entries older than (say) a week, the
> reflog for a topic branch that hasn't seen any activity may become
> empty.  Then I "git am" the new round on the same base, compare and
> then update, perhaps like so:
> 
>     ... git reflog expire has emptied the log for so/topic ...
>     $ git checkout so/topic
>     $ git log master.. ;# remind myself what the previous round had
>     $ git checkout master... ;# detach HEAD at the previous base
>     $ git am -s ./+so-v2-topic ;# apply
>     $ git range-diff @{-1}... ;# compare
>     $ git checkout -B so/topic
> 
> Now, I'm used to see this work after the above:
> 
>     $ git range-diff @{1}... ;# compare again just to be sure
> 
> but because there is only one entry in the reflog, which was created
> when the last "checkout -B" updated the so/topic branch, "there is
> only one entry" error kicks in.
> 
> > Makes sense. The first solution that comes to mind is immediately record
> > current state after "reflog expire", so that there will be 2 entries for
> > the case in question.
> 
> Perhaps.  
> 
> Or we could change the lookup side to use the value of the ref
> itself when asked for @{0}, and use the "old" side of the only entry
> when asked for @{1}.  That way, we do not need to play games with an
> artificial entry at all, which may be a better solution.

>> Or we could change the lookup side to use the value of the ref
>> itself when asked for @{0}, and use the "old" side of the only entry
>> when asked for @{1}.  That way, we do not need to play games with an
>> artificial entry at all, which may be a better solution.
>
> Or more generally, use the old side from @{n} when asked for @{n+1} when
> there are only n entries in the reflog.