libinput without udev

[Michael Forney]

Hi libinput developers,

libinput seems like a nice project and I would like to use it the only
input implementation for my compositor, swc (currently it is optional
and there is also a rudimentary EV_REL-only implementation).

Unfortunately, even though libinput provides a "path" context which
allows the caller to add and remove devices explicitly, libudev is a
hard dependency.

I took a look at making libudev optional, and it seems possible to keep
the existing API, by returning NULL from libinput_udev_create_context
and libinput_device_get_udev_device and using a forward declaration of
the udev structs in libinput.h rather than including libudev.h. Maybe an
option like mesa's --enable-sysfs would be appropriate. However, I
wonder if such a patch would be considered upstream (I realize that this
might be a little controversial) or if I am wasting my time.

Currently, libinput is the only system component I would like to use
that has a hard libudev dependency, so unless libinput would consider
making this optional, I'll have to figure out something else.

Thanks