Consider using XDG directory structure for cabal in CI

[ulysses4ever]

As discussed in #8840, due to caching, our CI is probably stuck with ~/.cabal currently. It may be a good idea to wipe the cache and see where it brings us. Also, maybe it makes sense to add some diagnostics in the CI to make it more clear which setup we use (legacy or XDG).

As we’re using setup-haskell action, this is related:

• Output cabal-store: Use XDG directory structure for cabal 3.10? actions#210

[andreasabel]

Can cabal tell me where it likes to store stuff? Something like stack path.

$ stack path --stack-root
~/.stack

[mouse07410]

Can cabal tell me where it likes to store stuff? Something like stack path.

$ stack path --stack-root

~/.stack

I strongly support this.

[ulysses4ever]

Well, there's a simple/ish algorithm written out in https://cabal.readthedocs.io/en/3.10/config.html#directories:

Unless the CABAL_DIR environment variable is set or a ~/.cabal directory exists, Cabal will by default store data in directories according to the XDG Base Directory Specification.
...
$XDG_STATE_HOME/cabal for compiled libraries and other stateful artifacts, including the Cabal store.

But perhaps it would be handy to have such an interface to query cabal...

[andreasabel]

But perhaps it would be handy to have such an interface to query cabal...

Yes, indeed, otherwise each tool around cabal has to duplicate this logic.