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Re: [PATCH 0/2] Avoiding errors when partial cloning a tagged blob


Junio C Hamano wrote:
>> Jonathan Tan <jonathantanmy@xxxxxxxxxx> writes:

>>> When cloning a repository with a tagged blob (like the Git repository)
>>> with --filter=blob:none, the following message appears:
>>>         error: missing object referenced by 'refs/tags/junio-gpg-pub'
>>> and the resulting repository also fails fsck.
>                            Naïvely, I may expect fsck to follow the
> same principle--when it encounters a reference to an object that is
> deliberately missing, refrain from complaining, regardless of the
> place the offending reference was found, be it inside a tree object
> or a ref.
> Perhaps that line of consistent behaviour may be impossible due to
> the way the reference is stored inside a tree object and a ref?

Yes, exactly.  I believe this is why we did not treat refs as
promisors when we introduced promised objects.

We could revisit that decision and make refs into promisors, storing
any extra metadata on the side.  That would be a more invasive change
than this series does, though.  In the model used today, where refs
are not promisors, this series is the logical thing to do.

> E.g. a reference to an expected-to-be-missing blob still lets us
> know that the missing object is expected to be a blob, but a ref
> only stores the object name and not its type, so we can tell it is
> missing, but we cannot say it is OK to be missing because we expect
> it to be a blob, or something?

The main downside of saying that filters should not be applied to the
objects named directly in a "want" is that such objects could be large.

The upsides are that

- it makes the protocol more consistent with the current invariants
  maintained by "git fsck"

- down the line, it should make operations like "fetch just this one
  tree" a little simpler, since you can use

   filter blob:none
   filter tree:none
   want <this tree>

Later we could introduce a separate kind of "want" for which filters
apply to the object named directly, too, to provide more flexibility
for the client.  I can imagine cases where a person would want each of
those two behaviors, so I don't think we are incurring unnecessary
complexity by always sending the object named in a "want" without such
an explicit filtering request.  So I'm comfortable with the direction
this series goes in, though I haven't looked at the patches in detail.