[Haskell-cafe] Help test XDG support in cabal-install

[Troels Henriksen]

Cabal, or more precisely cabal-install which is mostly known to
Haskellers as the cabal command line program, recently merged a pull
request that makes cabal support the XDG Basedir
Specification. Previously, cabal would put all of its files in the
~/.cabal directory. Now the files are spread over multiple directories:

  * $XDG_CONFIG_HOME/cabal for the main configuration file. On Unix,
    this defaults to ~/.config/cabal.

  * $XDG_CACHE_HOME/cabal for downloaded packages and script
    executables. Defaults to ~/.cache/cabal on Unix.

  * $XDG_STATE_HOME/cabal for compiled libraries and other stateful
    artifacts. Defaults to ~/.local/state/cabal on Unix.

  * ~/.local/bin for executables installed with 'cabal install'.

The advantage is mostly that cabal now behaves slightly more like other
modern Unix tools. For example, it is easier to put all configuration
files under version control if they’re all in the same subdirectory, and
it is easier to delete all program caches when you’re low on disk space.

This is obviously a rather invasive change. Does it mean that the next
version of cabal will break your workflow? Maybe! But if so, it is not
intentional. This change comes with what I hope is rather thorough
backwards compatibility behaviour. Basically, if ~/.cabal exists, or
$CABAL_DIR is set, the old behaviour of using a single unified directory
will be maintained. And of course, most paths can still be configured
manually in the configuration file.

Still, because of the delicacy of a change like this, we’d like some
external confirmation that cabal is still usable. This requires human
trials. Therefore, if you are a human who uses cabal, please try
installing the latest development version and see if it still works for
you. If you want to try out the new XDG future, you can delete your
~/.cabal directory (possibly copying ~/.cabal/config to
~/.config/cabal/config first). I’ve been dogfooding this support for a
over month, but I have no illusions about my usage covering the full
feature space.

Beyond whether cabal remains at all functional, I am personally curious
whether the XDG simulacrum that is implemented on Windows is at all
useful for Windows users, or whether it would be better for cabal to
retain a single unified directory on that platform.

Finally, on a meta note, this is my first contribution to Cabal. I
previously heard horror stories about its code complexity, but I don’t
think think they are warranted, at least not in the corner that I was
touching. You certainly find relics of a long development process,
including code necessary to support obsolete features (v1-build and
sandboxes), but for a project its age and scope, I found the code both
well structured and reasonably well documented. XDG support was added
entirely by modifying cabal client code, without touching the Cabal
library at all.

-- 
\  Troels
/\ Henriksen