At the command prompt, if you try to load a filename with no extension:

load somefile

It'll try these in order:

somefile
somefile.p8
somefile.p8.png

It'd be nice if #include worked the same way.

e.g. with vector.p8 in the same folder:

#include vector

I think simply re-using the logic from load would work, because it behaves exactly the way I'm suggesting.

As for Lua files, it's probably best if the .lua extension has to be typed out explicitly, because you're essentially leaving the sphere of PICO-8 by using a raw lua file and it makes sense that PICO-8's name abbreviation would not apply. Plus this is the same behavior load already uses, so minimum effort required. ;)

@zep

Gonna ask for this one again, I still think it'd be a nice QoL feature.