Re: [WIP PATCH 0/3] implement merge strategy for submodule links

From: Jens Lehmann <jens.lehmann@web.de>
Date: Jun 16, 2010, 17:16 UTC
Message-ID: <4C1906FA.7010906@web.de>
In-Reply-To: <201006160205.20705.johan@herland.net>

Am 16.06.2010 02:05, schrieb Johan Herland:

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> - If the purpose is to re-use existing submodule merges then I'm afraid (as 
> I've argued above) that this would happen too seldom to be useful in 
> practice (and even then you would already have had to set up the appropriate 
> config for your branch, to enable Git to find this pre-existing merge at 
> all).

That this is all but happening seldom for us is the reason for this WIP patch from Heiko. And other use cases won't be harmed by this change, no? And if some are, we can add a config option to .gitmodules to control that.

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> Taking a step back and comparing the merging of submodules vs. the merging 
> of regular files:
> 
> Git's rules are simple and straightforward for regular files: If both 
> sides/branches have changed the same area of code (and the changes don't 
> exactly coincide), you get a conflict. There's no magic/cleverness applied 
> to try to figure out what a good resolution would look like; it's a 
> conflict, and the user must resolve it. Simple as that.
> 
> I'd argue that the submodule case should be the same: If both sides/branches 
> change the submodule (and the SHA1s don't exactly match), you get a 
> conflict, and it's up to the user to resolve it.
> 
> We may to make an exception for the case where one SHA1 is a descendant of 
> the other (i.e. a fast-forward situation), since that seems like a safe 
> choice in most situations, but I don't feel safe doing much beyond that.

Yes, I would like to see that fast-forward case silently handled by a merge in the superproject.

And if it is no fast-forward but you find a unique merge where both of these SHA1s are included, you could advertise it as a possible solution but not automagically add it to the index. So you give the maintainer of the superproject the opportunity to assess a possible solution but spare him the chore of trying to find the reason why the merge failed and what he can do about it by showing him the right direction. He might then decide to take a later commit of the submodule or resolve the whole issue differently, but that is up to him.

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>> And for me the first commit containing the others is the one I would like
>> to see then.
> 
> In that case you will have to modify Heiko's patches, because (I believe) 
> they currently choose the _latest_ commit containing the others...

Yes, but IMHO that is a bit too much forwarding.