Merge driver not called for locally modified files?

[Gioele Barabucci <gioele@svario.it>]

Hello,

it seems to me that merge drivers are not called while merging commits
that touch locally modified (but uncommited) files. Is this correct?

I made a (simple) merge driver for files in the `pw` format. [1] This
driver works correctly when a file is modified by multiple commits.
However, if a file has only been modified locally (and not committed),
then merging a commit that modifies the same file raises the following
error:

    $ git merge --ff-only 78d4f09
    Updating 5180202..78d4f09
    error: Your local changes to the following files would
    be overwritten by merge:
	.local/share/pw/passwords
    Please, commit your changes or stash them before you can merge.
    Aborting

>From my experiments, it looks like the merge driver is not called at all.

Is it possible to configure git so that the merge driver is called also
while merging locally modified files?

Regards,

[1] https://github.com/gioele/pw/blob/master/bin/git-pw-merge

-- 
Gioele Barabucci <gioele@svario.it>