A single variable to override base folder for `user_*_dir` functions

[Czaki]

Extension of #347

When working on a caching of cache directory between sessions on CI I found that I could easily overwrite the cache directory location on Linux (using XDG_CACHE_DIR)

Then I cannot overwrite it on macOS without overwriting the whole $HONE.

platformdirs/src/platformdirs/macos.py

Lines 65 to 68 in c945a28

	@property
	def user_cache_dir(self) -> str:
	""":return: cache directory tied to the user, e.g. ``~/Library/Caches/$appname/$version``"""
	return self._append_app_name_and_version(os.path.expanduser("~/Library/Caches")) # noqa: PTH111

It looks like there is an option to overwrite it on Windows:

platformdirs/src/platformdirs/windows.py

Lines 69 to 76 in c945a28

	@property
	def user_cache_dir(self) -> str:
	"""
	:return: cache directory tied to the user (if opinionated with ``Cache`` folder within ``$appname``) e.g.
	``%USERPROFILE%\\AppData\\Local\\$appauthor\\$appname\\Cache\\$version``
	"""
	path = os.path.normpath(get_win_folder("CSIDL_LOCAL_APPDATA"))
	return self._append_parts(path, opinion_value="Cache")

(will have access to a Windows machine in a few days, then could check)

But it will really simplify CI configuration if there is one environment variable respected on all OS. For example: PLATFORMDIR_CACHE_DIR. (And similar variables for other directories)

What did you think about such a feature? Will you accept such a contribution?

Related PR that brings me this idea: napari/napari#8235

[gaborbernat]

What did you think about such a feature? Will you accept such a contribution?

I'm +0 on this. I'd rather not add it myself, and have XDG_ work on unix and have WIN_PD_OVERRIDE_ for Windows, but if the other maintainer @ofek think it's good idea I'll approve.

[Czaki]

I'm +0 on this. I'd rather not add it myself, and have XDG_ work on unix and have WIN_PD_OVERRIDE_ for Windows,

So add support of XDG_* to macos.py file?

[gaborbernat]

So add support of XDG_* to macos.py file?

Yes 👍

[ofek]

I'm still thinking but what is WIN_PD_OVERRIDE_?

[gaborbernat]

I'm still thinking but what is WIN_PD_OVERRIDE_?

See #347 (comment)

[gaborbernat]

All platforms now support environment variable overrides:

Platform	Override mechanism	Added in
Linux	XDG_* env vars via XDGMixin	(always supported)
macOS	XDG_* env vars via XDGMixin	#375
Windows	WIN_PD_OVERRIDE_* env vars	#428

For example, setting XDG_CACHE_HOME works on both Linux and macOS to redirect cache directories — no need for a separate cross-platform variable. On Windows, WIN_PD_OVERRIDE_LOCAL_APPDATA covers the equivalent use case.