threads / discuss / 35590

Re: aborted 'git fetch' leaves workspace unusable

Subject: Re: aborted 'git fetch' leaves workspace unusable

## tl;dr

4 messages between Dec 31, 2013 and Jan 3, 2014.

replies: 3people: 2as markdown or json

stephen_leake@stephe-leake.org· Dec 31, 2013, 08:19 UTC · lore

Junio C Hamano <gitster@pobox.com> writes:

Show 17 quoted lines

> stephen_leake@stephe-leake.org writes:
> 
>> That left the workspace unusable:
>> 
>> - .git/FETCH_HEAD is empty
>> 
>>     that causes 'git rev-parse FETCH_HEAD' to fail with a confusing
>>     error message.
> 
> This is not limited to your Cygwin environment.  I can see that we
> leave an empty file there after a failed fetch with
> 
> 	$ git fetch ssh://no.such.place/
> 
> But I would not call it leaving "the workspace unusable".  If you
> ask "git rev-parse" "What is in FETCH_HEAD?", you would get "that is
> not even a revision", which is what you would get.

Yes, and I also discovered that FETCH_HEAD is not present after a clone. So in general I need to be tolerant of an empty/missing FETCH_HEAD (I'm actually working on an Emacs front end for git).

However, in this case, even running the fetch was a mistake; I would have prefered that it leave FETCH_HEAD in its previous state. Is there any way to reconstruct it? refs/heads/master was untouched, but I don't know how to find the fetched head.

Show 10 quoted lines

>> - 'git fetch' just hangs after outputting:
>> 
>> remote: Counting objects: 15, done.
>> remote: Compressing objects: 100% (8/8), done.
>> remote: Total 9 (delta 5), reused 0 (delta 0)
> 
> This looks more serious, but I suspect it is totally unrelated to
> your previous fetch failing and leaving FETCH_HEAD there.  Is this
> "'git fetch' hangs" reproduce in a clean clone _without_ first
> encountering the failure (due to the forgotton "ssh-add")?

no, the clone worked (so the network is up, the server is up), and a subsequent 'git fetch' did not hang. Although there was also nothing to fetch.

I'll have to wait until there is something to fetch, and see if I can reproduce the bug. Or set up a git server and test branch - not high enough on my priority list.

-- -- Stephe

Junio C Hamano· Jan 2, 2014, 18:09 UTC · re: stephen_leake@stephe-leake.org · lore

stephen_leake@stephe-leake.org writes:

> However, in this case, even running the fetch was a mistake; I would
> have prefered that it leave FETCH_HEAD in its previous state.

I think the clearing of leftover FETCH_HEAD is one of the early things "git fetch" does, unless "--append" is in effect. I haven't looked at the code for a long time, but it may be possible to move the logic of doing so around so that this clearing is done as lazily as possible.

I however suspect that such a change may have fallouts on other people who are writing tools like yours; they may be depending on seeing FETCH_HEAD cleared after a failed fetch, and be surprised to see a stale contents after they (attempt to) run "git fetch" in it.

So it is not so clear if it is a good thing to change the behaviour of "git fetch" not to touch FETCH_HEAD upon a failure.

Stephen Leake· Jan 3, 2014, 03:28 UTC · re: Junio C Hamano · lore

Junio C Hamano <gitster@pobox.com> writes:

Show 18 quoted lines

> stephen_leake@stephe-leake.org writes:
>
>> However, in this case, even running the fetch was a mistake; I would
>> have prefered that it leave FETCH_HEAD in its previous state.
>
> I think the clearing of leftover FETCH_HEAD is one of the early
> things "git fetch" does, unless "--append" is in effect.  I haven't
> looked at the code for a long time, but it may be possible to move
> the logic of doing so around so that this clearing is done as lazily
> as possible.
>
> I however suspect that such a change may have fallouts on other
> people who are writing tools like yours; they may be depending on
> seeing FETCH_HEAD cleared after a failed fetch, and be surprised to
> see a stale contents after they (attempt to) run "git fetch" in it.
>
> So it is not so clear if it is a good thing to change the behaviour
> of "git fetch" not to touch FETCH_HEAD upon a failure.

Ok; backwards compatibility is important.

Perhaps FETCH_HEAD could be copied to FETCH_HEAD_prev or some such, to allow recovering in an error case?

-- 
-- Stephe

Junio C Hamano· Jan 3, 2014, 17:58 UTC · re: Stephen Leake · lore

Stephen Leake <stephen_leake@stephe-leake.org> writes:

Show 25 quoted lines

> Junio C Hamano <gitster@pobox.com> writes:
>
>> stephen_leake@stephe-leake.org writes:
>>
>>> However, in this case, even running the fetch was a mistake; I would
>>> have prefered that it leave FETCH_HEAD in its previous state.
>>
>> I think the clearing of leftover FETCH_HEAD is one of the early
>> things "git fetch" does, unless "--append" is in effect.  I haven't
>> looked at the code for a long time, but it may be possible to move
>> the logic of doing so around so that this clearing is done as lazily
>> as possible.
>>
>> I however suspect that such a change may have fallouts on other
>> people who are writing tools like yours; they may be depending on
>> seeing FETCH_HEAD cleared after a failed fetch, and be surprised to
>> see a stale contents after they (attempt to) run "git fetch" in it.
>>
>> So it is not so clear if it is a good thing to change the behaviour
>> of "git fetch" not to touch FETCH_HEAD upon a failure.
>
> Ok; backwards compatibility is important.
>
> Perhaps FETCH_HEAD could be copied to FETCH_HEAD_prev or some such, to
> allow recovering in an error case?

As FETCH_HEAD is purely ephemeral (so are other ephemeral markers like MERGE_HEAD and friends), and the promise between "git fetch" and its users has always been that an invocation of "git fetch" clears FETCH_HEAD (logical consequence of which is that the user runs "git fetch" only when s/he are _done_ with the old FETCH_HEAD), I doubt FETCH_HEAD_prev would add much value to the system and only introduce more things we have to worry about, like "when will it be cleaned?", "what happens to the old value in FETCH_HEAD_prev?".

It is like asking "Should 'rm -f foo' save the original 'foo' to somewhere else just in case?".

If your emacs wrapper for some reason needs to know what happened in the last fetch, I imagine that it can check and record what was in FETCH_HEAD before issuing "git fetch", so...