To help users migrate from the previous
settings to new freeform settings type,
the commit at hand adds some
`mkRemovedOptionModule` and `mkRenamedOptionModule`.
These modules are not designed to work
inside an attribute set of submodules.
They create values for `assertions` and
`warnings` to inform the user of required changes.
Also, these informational texts do not contain
the full attribute path of the changed options.
To work around these deficiencies,
we define the required options `assertions` and `warnings`
inside the submodule and later add the values collected
inside these options to the corresponding top-level options.
In the course of doing so, we also add the full attribute path
to the informational texts so the user knows these warning
and error messages refer to the `tsmClient.servers` option.
Also, we have to filter out `warnings`, `assertions`, and
the "old" options when rendering the target config file.
Check for spaces or duplicate names in server config keys.
Since server config keys are case insensitive,
a setting like
```
{
compression = "yes";
Compression = "no";
}
```
would lead to an ambiguous configuration.
`tsm-client` uses a global configuration
file that must contain coordinates for each
server that it is supposed to contact.
This configuration consists of text
lines with key-value pairs.
In the NixOS module, these servers may be declared
with an attribute set, where the attribute name
defines an alias for the server, and the value
is again an attribute set with the settings for
the respective server.
This is organized as an option of type `attrsOf submodule...`.
Before this commit:
Important settings have their own option within
the submodule. For everything else, there is
the "catch-all" option `extraConfig` that may
be used to declare any key-value pairs.
There is also `text` that can be used to
add arbitrary text to each server's
section in the global config file.
After this commit:
`extraConfig` and `text` are gone,
the attribute names and values of each server's attribute
set are translated directly into key-value pairs,
with the following notable rules:
* Lists are translated into multiple lines
with the same key, as such is permitted by
the software for certain keys.
* `null` may be used to override/shadow a value that
is defined elsewhere and hides the corresponding key.
Those "important settings" that have previously been
defined as dedicated options are still defined as such,
but they have been renamed to match their
corresponding key names in the configuration file.
There is a notable exception:
"Our" boolean option `genPasswd` influences the "real"
option `passwordaccess', but the latter one is
uncomfortable to use and might lead
to undesirable outcome if used the wrong way.
So it seems advisable to keep the boolean option
and the warning in its description.
To this end, the value of `getPasswd` itself is
later filtered out when the config file is generated.
The tsm-backup service module and the vm test are adapted.
Migration code will be added in a separate
commit to permit easy reversal later, when the
migration code is no longer deemed necessary.
