Subject: Re: git merge banch w/ different submodule revision

From: "Middelschulte, Leif" <[email-masked]>
Date: Wed, 2 May 2018 07:30:25 +0000

Am Montag, den 30.04.2018, 19:02 +0200 schrieb Heiko Voigt:
> On Thu, Apr 26, 2018 at 03:19:36PM -0700, Stefan Beller wrote:
> > Stefan wrote:
> > > See https://github.com/git/git/commit/68d03e4a6e448aa557f52adef92595ac4d6cd4bd
> > > (68d03e4a6e (Implement automatic fast-forward merge for submodules, 2010-07-07)
> > > to explain the situation you encounter. (specifically merge_submodule
> > > at the end of the diff)
> > 
> > +cc Heiko, author of that commit.
> 
> In that commit we tried to be very careful about. I do not understand
> the situation in which the current strategy would be wrong by default.
> 
> We only merge if the following applies:
> 
>  * The changes in the superproject on both sides point forward in the
>    submodule.
> 
>  * One side is contained in the other. Contained from the submodule
>    perspective. Sides from the superproject merge perspective.
> 
> So in case of the mentioned rewind of a submodule: Only one side of the
> 3-way merge would point forward and the merge would fail.
> 
> I can imagine, that in case of a temporary revert of a commit in the
> submodule that you would not want that merged into some other branch.
> But that would be the same without submodules. If you merge a temporary
> revert from another branch you will not get any conflict.
> 
> So maybe someone can explain the use case in which one would get the
> results that seem wrong?
In an ideal world, where there are no regressions between revisions, a
fast-forward is appropriate. However, we might have regressions within
submodules.

So the usecase is the following:

Environment:
- We have a base library L that is developed by some team (Team B).
- Another team (Team A) developes a product P based on those libraries using git-flow.

Case:
The problem occurs, when a developer (D) of Team A tries to have a feature
that he developed on a branch accepted by a core developer of P:
If a core developer of P advanced the reference of L within P (linear history), he might
deem the work D insufficient. Not because of the actual work by D, but regressions
that snuck into L. The core developer will not be informed about the missmatching
revisions of L.

So it would be nice if there was some kind of switch or at least some trigger.

Cheers,

Leif

> Cheers Heiko