Handle configuration imports

[vlinkz]

Currently only supports reading and editing a single file. Would be more useful if imports could be handled, read, and edited as well. Perhaps automatically detect a list, as well as support manually choosing files.

Related:
snowfallorg/nix-editor#7
#6

[ashkitten]

I was thinking about design for this as I try out SnowflakeOS. We might be able to avoid just slapping a filesystem tree in the user's face if we do this right. What do you think about a sort of "tags" UI where you can tag a value with what tags it applies to? Tags would correspond to modules, so would be hierarchical (import hierarchy, not filesystem). I made a very rough mockup of a possible UI:

In the image, the config root imports Desktop which imports Common, where the attribute is defined with mkDefault. However, it's overridden because the root also imports Server, so that section is desaturated.

We would have a separate UI as well, where the user would create Configurations and select Tags to include in each Configuration. These are sort of fuzzy details, and since each module is technically its own configuration it should probably be possible to convert between Configurations and Tags (i.e if someone wants to take an existing machine's config and generalize it into a tag or multiple tags).

As for the actual implementation, we could simply add a comment with special meaning to the file to represent its human-readable tag name.

Hope this makes sense and is helpful!