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

Sascha Silbe [off-list ref] 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