Add 'services.emacs.socketActivation.enable' for generating an
'emacs.socket' systemd unit.
Emacs since version 26 has supported socket activation, whereby an
external process manager such as systemd listens on a socket and passes
it to the Emacs daemon when the manager launches it. This improves
startup time of the user session and avoids launching the daemon when not
needed, for example when launching the user session via SSH.
This implementation hard-codes the socket path to the default for the
version of 'programs.emacs.finalPackage', because systemd does not
perform shell expansion in the socket unit's 'ListenStream' parameter
and it seems like an advanced use-case to change the socket path. Shell
expansion would be desirable as the socket path usually resides in
directories such as $XDG_RUNTIME_DIR or $TMPDIR.
Tests were added to verify behavior in the following cases:
- Emacs service with socket activation disabled
- Emacs 26 with socket activation enabled
- Emacs 27 with socket activation enabled
PR #1314
Before the XDG variables would be set from the user's environment, if
available. This would break some tests.
With this change the tests should be fully deterministic.
Fixes#1190
Add 'services.lieer', which generates systemd timer and service units
to synchronize a Gmail account with lieer. Per-account configuration
lives in 'accounts.email.accounts.<name>.lieer.sync'.
This replaces some derivation outputs by simple strings rather than
full Nix store paths. This removes the need to download the whole
derivation when all we need is a static string.
