bug#70605: greetd-wlgreet-session: invalid G-expression input

[Franz Geffke]

Hello everyone,

I'm seeing some issues with greetd-wlgreet-session.

According to the docs 
https://guix.gnu.org/manual/en/html_node/Base-Services.html I would assume that 
greetd-wlgreet-session and greetd-agreety-session are easily exchangeable, but 
greetd-wlgreet-session leads to an error, whereas greetd-agreety-session does not.

Here's the error:

```
guix system: error: #<<greetd-wlgreet-session> wlgreet: #<package 
wlgreet@0.4.1-1.7e79d60 gnu/packages/admin.scm:5602 7f90a2f8e9a0> command: 
#<file-append #<package sway@1.9 gnu/packages/wm.scm:1883 7f90aa657dc0> 
"/bin/sway"> command-args: () output-mode: "all" scale: 1 background: (0 0 0 
0.9) headline: (1 1 1 1) prompt: (1 1 1 1) prompt-error: (1 1 1 1) border: (1 1 
1 1) extra-env: ()>: invalid G-expression input
```

Here's what my service looks like:

```
(service greetd-service-type
  (greetd-configuration
    (greeter-supplementary-groups (list "video" "input"))
    (terminals
      (list

        ;; working
        (greetd-terminal-configuration
          (terminal-vt "1")
          (default-session-command
           (greetd-agreety-session)))

        ;; working
        (greetd-terminal-configuration
          (terminal-vt "1")
          (default-session-command
           (greetd-wlgreet-sway-session)))

        ;; not working
        (greetd-terminal-configuration
          (terminal-vt "1")
          (default-session-command
           (greetd-wlgreet-session)))

        (greetd-terminal-configuration
          (terminal-vt "2"))
          (greetd-terminal-configuration
          (terminal-vt "3"))
          (greetd-terminal-configuration
          (terminal-vt "4"))
          (greetd-terminal-configuration
          (terminal-vt "5"))
          (greetd-terminal-configuration
          (terminal-vt "6"))))))
```

Either I'm doing something wrong, or greetd-wlgreet-session does not work by 
itself. When I have time, I'll dig a little deeper.

Cheers,
Franz