Re: custom merge driver vs. CONFLICT (delete/modify)

[Jakub Narebski <jnareb@gmail.com>]

Sascha Silbe <sascha-ml-reply-to-2010-3@silbe.org> writes:

> I am (automatically) building snapshot packages by combining the packaging
> maintained in one repository (but also containing sources) with (more
> recent) upstream sources from another repository.
> 
> For some files (those touched by rerunning auto*) I want the local
> version to always take precedence. For some other files (autogen.sh, PO
> files) I want the upstream version to take precedence. For all the rest
> I want conflicts to produce an error.
> 
> This has worked fine so far by using custom merge drivers, but while
> adding the second one I encountered a problem: Merge drivers are only
> invoked for modify/modify (and maybe add/add) conflicts.
> More specifically a delete/modify conflict will cause git-merge to bail
> out directly without calling the merge driver to resolve the conflict.
> Such a conflict occurred because the packaging people removed autogen.sh
> (which is reasonable for them, but not for me).
> 
> Is there a way to either resolve all kinds of conflicts in favour of
> one side (like -X <side>) or always take one side (like -s <side>) for
> a specific set of files?
> Alternatively, is there a way to do a merge in multiple "steps",
> operating only on a subset of the files each time (so I can use
> -s <side> / -X <side> for two of three steps per merge)?

Well, you can create your own merge strategy (see git-merge-ours.sh
in contrib/examples/ as an example), put it in appropriate place,
and use '--strategy=<name>' to force using your own custom merge
strategy.

The problem you see is that merge *driver* (as set by gitattributes)
deals only with _file-level_ conflicts, i.e. it is run instead of
ordinary diff3-based merge.  The CONFLICT(Delete/modify) is solved on
the _tree_ level by a merge *strategy*.  Currently there is no way to
change how tree-level conflict is resolved, without creating your own
merge strategy.  Though in princile it doesn't seem impossible...

-- 
Jakub Narebski
Poland
ShadeHawk on #git