bug#50468: Should `guix deploy` save to the deployed server the operating-system, or the entire file passed into the command?

[Katherine Cox-Buday]

*Observed Behavior:*

Invoking `guix deploy my-config.scm` will store `my-config.scm` in the
deployed server's store, and links that as
`/run/current-system/configuration.scm`.

*Expected Behavior*

I expected the deployed server to only be made aware of the requested
`operating-system` declaration. In other words, `my-config.scm` contains
a list of machines, and each machine has an `operating-system`
declaration. I would expect each deployed machine to only have a copy of
their, and only their, `operating-system` declaration, fully resolved
from Guile variables into strings and such.

*Justification*

`guix deploy` expects a file that "evaluates to a list of machine
objects". Because of this, it is expected that multiple machines are
declared in a single file. These machines may not be related to each
other, and they may even have information that should be kept from one
another. Therefore, deploying the entire file's contents to a deployed
machine's remote store is incorrect behavior.

Further, `guix deploy` works if the file given does something like
`(load "my-private-stuff.scm")`. It will resolve the Guile variables
before deploying, and everything will work. But the `configuration.scm`
on the deployed server will only have a reference to the `load` which
won't be in the store. The unresolved Guile variables will be listed
where they are used.

*Workaround*

Each machine can reside in a separate file, and then `guix deploy` can
be executed for each file with:

find . -iregex '.*\.scm' -print -execdir guix deploy "{}" \;

-- 
Katherine