Display lru_cache cache_info in very verbose mode?

[blueyed]

With the recent addition of functools.lru_cache it might make sense to display its cache_info with -vvv or some other flag, which would be helpful when investigating performance.

For this it might make sense to wrap it into a separate module, so that it is easier to handle all of them (currently just one, but two already with #4247).

[nicoddemus]

Sounds good. The idea is to show cache_info for all lru_cache-decorated functions?

[blueyed]

Yeah.

[asottile]

Maybe instead of hooking into -v (I often spam -vvvvv since I can't remember how many it is and surely a few extra won't hurt -- and I don't think this info will be helpful in that case), we add a plugin that's something along the lines of --show-lru-cache-info?

[asottile]

@isidentical is looking into taking this one -- we're discussing some implementation details about this

what I think we're going to do for a first pass is:

• add a new plugin module to handle "internal pytest... stuff" for lack of a better name (maybe debug? internal? meta? idk, naming is hard)
• in this module, add an option like above
• add a reporting mechanism that uses pkgutil or some such to iterate through the _pytest namespace looking for globals with lru_cache attached

or something like that? thoughts?