configure .cache via $XDG_CACHE_DIR

[bukzor]

Forked from #1029

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a) A very convenient, and standard, way to configure tools' cache location is to set $XDG_CACHE_DIR. Many of my project's fixtures do this for other reasons already. Similarly, the most convenient, and standard, way to set "basetmp" would be $TMPDIR.

b) "something a CI system can easily pick up" is exactly these environment variables. Many systems will already support this, and those that don't will support injecting environment variables.

c) "non-containered ci" will either support ~/.cache correctly, or set $XDG_CACHE_DIR, because this is necessary for other tools that use the standard. Again, this is already handled in many of my projects because of other tools.

[RonnyPfannschmidt]

is there a good package that helps finding those paths and helps clearing unused caches

after all if the cache folder is outside of the working directory,
its lifetime is unrelated to the working directory

imagine for example a unaware ci system that makes one folder per build could easily DOS the ci server due to filling up ~/.cache of the ci user

with the current mode of operation, cache and working directory are simply co-located and share a lifetime, so data management is easy, the cache is gone when one deletes the working directory

im not per se opposed to following XDG, but it makes lifetimes of file-system objects more tricky on our case and seems not really available on windows either
(its my personal impression that xdg works only well on posix boxes with a typical linux/bsd setup)

[bukzor]

Those are good points...

I don't have a good answer. The applications I've seen don't worry about cleaning up like that.
It would work for me if we use the current behavior when XDG_CACHE_DIR doesn't exist.

@asottile

[bukzor]

This one at least helps find a good platform-specific cache dir: https://pypi.python.org/pypi/appdirs/1.4.0

[bukzor]

This one helps manage expiry for a file-based cache.
Making one of the keys be the working directory would make it work.

http://pythonhosted.org/pyfscache/

[RonnyPfannschmidt]

i shorty investigated appdirs and pyfscache, unfortunately both are unsuitable

appdirs seems bug-ridden
pyfscache is for something entirely different not fitting the use-case

[RonnyPfannschmidt]

how about introducing a ini value/env variable to select the cache backend,
which defaults to worktree, but one can choose xdg/disabled?

@hpk42 oppinions?

[asottile]

Personally I'd rather default to xdg instead of needing to add .cache to the gitignore in every one of my projects

[RonnyPfannschmidt]

while i agree that it is a nice default, we cant do a change like that befor 3.0

also before we can do it propperly we need to come up with a solid way to clean things up

[asottile]

Maybe introducing the cache plugin defaulted to on should have been in 3.0 too :/

[RonnyPfannschmidt]

since its a normal feature addition, it doesnt warrant a release that large

[s-trooper]

i hate ".cache" folder for aesthetic reason. my projects folders are already populated by ide, git, python and others "support folders". sometimes i have more folders than actually python program files! please make ".cache" location configurable!

[nicoddemus]

how about introducing a ini value/env variable to select the cache backend

Anyone is against this? While it may not be the best option, it is simple to implement and backward compatible.

It should support variable expansion and default to .cache for backward compatibility. This would allow users to change it like this:

[pytest]
cache_dir=$XDG_CACHE_DIR

Or use an environment variable:

PYTEST_CACHE_DIR=/some/path

[RonnyPfannschmidt]

I'm against the most easy variant, I want a simple solution