Re: If a branch moves a submodule, "merge --ff[-only]" succeeds while "merge --no-ff" fails with conflicts

From: Dakota Hawkins <dakotahawkins@gmail.com>
Date: Sep 6, 2016, 20:02 UTC
Message-ID: <CAG0BQX=FFWqR=45g6buujzK2jknx8aZnQoiV_m-QZhcx4Dd52g@mail.gmail.com>
In-Reply-To: <CAGZ79kb=LyusFH6tGirGP9qK1k-cov2UubEbKPfeyPRThUsa-Q@mail.gmail.com>

On Tue, Sep 6, 2016 at 3:00 PM, Stefan Beller <sbeller@google.com> wrote:

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> On Fri, Sep 2, 2016 at 12:22 PM, Dakota Hawkins <dakotahawkins@gmail.com> wrote:
>> Below is a simple reproduction of the issue.
>>
>> The _real_ problem is that this is how our pull request merges work,
>
> So your workflow is the problem or is the actual bug just exposed in
> your workflow?

I believe the workflow just exposes the problem, which is that generically for this case a fast-forward merge works without conflicts while a non-fast-forward merge fails with conflicts. Sorry if this confuses the issue, it's just how we experienced it so I wanted to add that background.

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>> ## Test fast-forward merge, this will work
>> git checkout -b merge-ff-test master # warning: unable to rmdir
>> submodule-location-2: Directory not empty
>> rm -rf ./submodule-location-2
>> git merge --ff-only move-submodule
>>
>
> And no reset/rm in between, i.e. we still have
> submodule-location-2 from  merge-ff-test still around?

That is true in that example, but somewhat immaterial. The first merge was only to demonstrate that a fast-forward merge works without conflict. The simplest reproduction is to skip that and get straight to the failure case:

## Clone and setup branches git clone https://github.com/dakotahawkins/submodule-move-merge-bug-main-repo.git cd submodule-move-merge-bug-main-repo git branch move-submodule origin/move-submodule git checkout -b merge-no-ff-test master

## This will fail git merge --no-ff move-submodule # Auto-merging submodule-location-2 # Adding as submodule-location-2~move-submodule instead # Automatic merge failed; fix conflicts and then commit the result.

Does that make things a little bit clearer?

Dakota