Re: [PATCH] submodules: allow empty working-tree dirs in merge/cherry-pick

[Stefan Beller <sbeller@google.com>]

On Mon, Nov 7, 2016 at 12:38 PM, David Turner <David.Turner@twosigma.com> wrote:
>> -----Original Message-----
>> From: Stefan Beller [mailto:sbeller@google.com]
>> Sent: Monday, November 07, 2016 2:14 PM
>> To: David Turner
>> Cc: git@vger.kernel.org
>> Subject: Re: [PATCH] submodules: allow empty working-tree dirs in
>> merge/cherry-pick
>>
>> On Mon, Nov 7, 2016 at 10:31 AM, David Turner <dturner@twosigma.com>
>> wrote:
>> > When a submodule is being merged or cherry-picked into a working tree
>> > that already contains a corresponding empty directory, do not record a
>> > conflict.
>> >
>> > One situation where this bug appears is:
>> >
>> > - Commit 1 adds a submodule
>>
>> "... at sub1" as inferred by text below.
>>
>> > - Commit 2 removes that submodule and re-adds it into a subdirectory
>> >        (sub1 to sub1/sub1).
>> > - Commit 3 adds an unrelated file.
>> >
>> > Now the user checks out commit 1 (first deinitializing the submodule),
>> > and attempts to cherry-pick commit 3.  Previously, this would fail,
>> > because the incoming submodule sub1/sub1 would falsely conflict with
>> > the empty sub1 directory.
>>
>> So you'd want to achieve:
>>   $ # on commit 3:
>>   git checkout <commit 1>
>>   git cherry-pick <commit 3>
>>
>> which essentially moves the gitlink back to its original place (from
>> sub1/sub1 -> sub1).  This sounds reasonable.
>> But what if the submodule contains a (file/directory) named sub1? We'd
>> first remove the sub1/sub1 submodule (and even delete the inner
>> directory?), such that "sub1/"
>> becomes an empty dir, which is perfect for having a submodule right there
>> at "sub1/"
>
> I'm confused about the "what if" here.
>
> In our particular situation, the submodule in question was not initialized.

oops. That explains it. I somehow assumed we were talking about
initialized submodules.

>
> If your approach also fixes the same tests that mine fixes, then I am happy to use your series over mine.  Please CC me so I can take a peek.

No, my series seems to be orthogonal to this one. I plan
on cc'ing you nevertheless as it is still nearby.

> basically nobody needs two copies of one submodule in the same repo.

IIRC this is how gitlinks were used in very early days :/
(kernel people were using gitlinks to track different kernel versions
and see if they were interoperable or working at all.
e.g. see d92a39590d1126e195f1bbccf182a2cdb79218e7, which
only makes sense (for the update command) if the referenced repository
contains references of all submodules, which either means a huge reference
pile that contains different projects at the same time, or the same project
at different versions.

>  I think that case fails for other reasons anyway.
>

Yes. I agree that the patch as-is is applicable. I did not try to oppose
your approach, but rather give some thoughts I had.

Stefan