On Tue, Feb 01 2022, Junio C Hamano wrote:
> Han-Wen Nienhuys <hanwen@xxxxxxxxxx> writes:
>
>>> Because there is no generic reflog API that says "enable log for
>>> this ref", a test that checks this feature with files backend would
>>> do "touch .git/refs/heads/frotz".
>>
>> There is refs_create_reflog(), so the generic reflog API exists. The
>> problem is that there is no sensible way to implement it in reftable.
>
> Ah, yes, that's correct.
>
>> One option is (reflog exists == there exists at least one reflog entry
>> for the ref).
>
> Because the current callers of refs_create_reflog() does want a
> reflog created that does not give any entry when iterated, I agree
> with you that adding a "fake" reflog entry alone is not a sufficient
> emulation of the API. I think these are all ...
>
>> This messes up the test from this patch, because it
>> creates a reflog, but because it doesn't populate the reflog, so we
>> return false for git-reflog-exists.
>>
>> It also turns out to mess up the tests in t3420, as follows:
>>
>> ++ git stash show -p
>> error: refs/stash@{0} is not a valid reference
>>
>> I get
>>
>> reflog_exists: refs/stash: 0
>>
>> and "git stash show -p" aborts with "error: refs/stash@{0} is not a
>> valid reference".
>
> ... indications of hat.
>
> I wonder if it is simple and easy to add a new reflog entry type
> used as an implementation detail of the reftable. If we can do so,
> then, the reftable backend integrated to the ref API can do these
> things:
>
> - reflog_exists() can say yes when one reflog entry of any type
> (internal to the reftable implementation) exists for the ref;
>
> - create_reflog() can add a reflog entry of the "fake" type
> (internal to the reftable implementation);
>
> - for_each_reflog_ent() and its reverse can learn to skip such a
> fake reflog entry.
>
> As there is no way to ask, via the API, the number of the existing
> reflog entries, the ref API callers would not be able to tell such
> an implementation detail that with reftable backend, create_reflog()
> does not create an empty reflog. To them, a reflog created with the
> API call would truly be empty as iterators will not return anything.
We could surely add magic record types, but how would such a dance be
performed while keeping compatibility with existing JGit clients?
