There is a need to manage XDG Base Directory system directory
environment variables in Home Manager modules. There is an existing
mechanism in `targets.genericLinux.extraXdgDataDirs', but this does not
apply to NixOS systems.
Furthermore, it is important that `XDG_CONFIG_DIRS' and `XDG_DATA_DIRS'
are set in both login shells (to support getty and SSH sessions) as well
as the systemd user manager (to propagate them to user services and
desktop environments).
The first need is addressed by adding the `xdg.systemDirs' module, which
configures lists of directory names for both `config' and `data'
directories. These are then set in
`$XDG_CONFIG_DIR/environment.d/10-home-manager.conf' and picked up by
the systemd user manager.
To make these, and other variables set in
`systemd.user.sessionVariables', available in login shells, an
additional step is added to `etc/profile.d/hm-session-vars.sh' which
exports the result of
`user-environment-generators/30-systemd-environment-d-generator' which
is shipped with systemd. The effect of this generator is to print
variables set on the systemd user manager such that shells can import
these into their environment.
Add new options Darwin options:
- `targets.darwin.defaults`
This adds options for configuring macOS through the `defaults(1)` system.
This option can be used to manipulate a vast majority of user settings for macOS
and its applications.
This is implemented using freeform modules and includes additional descriptions
and type information for some useful options.
- `targets.darwin.keybindings`
This adds options for configuring the default keybindings for macOS text fields.
- `targets.darwin.search`
This adds options for configuring the default search engine for macOS.
