xmonad: add support for v0.17.0

[NickHu]

Description

Starting from
~v0.17.0,
xmonad moved the location of its recompile output binary. This change
accommodates that. We might want to drop support for v0.15.0 at some point,
when it hits stackage LTS making haskellPackages.xmonad resolve to v0.17.0
(currently, it does not, although there is a separate
haskellPackages.xmonad_0_17_0).

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/use-latest-version-of-xmonad-0-17-0/16191/13

[berbiche]

Thanks!

Where does xmonad save its file when it recompiles the program now?
The symlink might have to be changed here:

home-manager/modules/services/window-managers/xmonad.nix

Lines 165 to 174 in 08e2d2a

	home.file.".xmonad/xmonad.hs".source = cfg.config;
	home.file.".xmonad/xmonad-${pkgs.hostPlatform.system}" = {
	source = xmonadBin;
	onChange = ''
	# Attempt to restart xmonad if X is running.
	if [[ -v DISPLAY ]]; then
	${config.xsession.windowManager.command} --restart
	fi
	'';
	};

[NickHu]

It moved from $XMONAD_DATA_DIR to $XMONAD_CACHE_DIR:

https://github.com/nix-community/home-manager/pull/2522/files#diff-47cbc76991d0d9b568f0f62b0b31aee6f69652b7302a7e1836e7adbe65041cc5R135-R141

The snippet you linked is just about where home-manager links the output of this, so it doesn't require any changes.

[berbiche]

If we change xmonad to use XDG (available since 0.17) then we would need to symlink the compiled binary to XDG_CACHE_HOME,
see:

• https://github.com/xmonad/xmonad/blob/eb2ee340e4180d1f7741605d846b154e777b509b/src/XMonad/Core.hs#L501-L545
• https://github.com/xmonad/xmonad/blob/eb2ee340e4180d1f7741605d846b154e777b509b/src/XMonad/Core.hs#L562-L564

[mentalblock]

If we change xmonad to use XDG (available since 0.17) then we would need to symlink the compiled binary to XDG_CACHE_HOME, see:

* https://github.com/xmonad/xmonad/blob/eb2ee340e4180d1f7741605d846b154e777b509b/src/XMonad/Core.hs#L501-L545

* https://github.com/xmonad/xmonad/blob/eb2ee340e4180d1f7741605d846b154e777b509b/src/XMonad/Core.hs#L562-L564

Ahhh. I think I understand what you mean. The symlink should now be something like

home.file."${config.xdg.cacheHome}/xmonad/xmonad-${pkgs.hostPlatform.system}" = { ...

for xmonad 0.17.

I do not know Nix that well so what would be the idiomatic way to make this conditional predicated on the version of xmonad?

EDIT: Fixed symlink path.

[mentalblock]

Can we merge this as is and fix the XDG path after 0.17.0 is the default version?

[NickHu]

@berbiche Oh, I see, you are proposing a bigger change where we transition to using XDG. As is, the patch currently works because the module explicitly sets XMONAD_*_DIR.

I agree with what @mentalblock said: it's probably best to wait until 0.17.0 is the default version to incorporate this larger change.

[berbiche]

Alright 👍