Use the same default cache directory across platforms?

[marktsuchida]

Currently cjdk uses, by default, the platform-specific cache directory on macOS and Windows. While this has some advantages, it also adds complexity: for example, a script that would like to clear the cjdk cache would need to branch by platform (or we'd need to provide a way to query the current cache directory).

Also, it appears that tools that are likely to be used in conjunction with cjdk tend to use the same directory on every platform:

• pipx uses ~/.local on all platforms
• jgo uses ~/.jgo (and, indirectly, ~/.m2) on all platforms
• pre-commit uses ~/.cache on all platforms

Although cjdk could be used internally by a user-facing app, it is more commonly a programmer/devops tool, so writing to ~/.cache even on Windows is probably not going to be frowned upon (and end-user apps can always override the cache directory).

So let's default to ~/.cache/cjdk on all platforms.

(Need to decide whether to still allow overriding via $XDG_CACHE_HOME. I think yes, but check what others do.)

[ctrueden]

I think respecting XDG_CACHE_HOME is a really good idea.

About defaulting to ~/.cache/cjdk on all platforms, I have no strong opinion... I think respecting the platform-specific defaults is probably better but I see the advantages of both.

What you could do, regardless, is add a flag to the cjdk tool that simply prints the cache directory. Something like cjdk --print-cache-dir. Then downstream tooling that wants to automate deletion of the cache has an easy way to find out where it is.