Expose the platform wrapper modules as the Nixvim configuration options
`build.nixosModule`, `build.homeModule`, and `build.nixDarwinModule`.
This makes it possible to reuse a single Nixvim configuration across
NixOS, Home Manager, and nix-darwin without re-importing modules into
`programs.nixvim` manually.
Evaluating these wrapper modules requires a "bare" Nixvim configuration;
one that does not define `pkgs` or `nixpkgs.hostPlatform`. Such a
configuration would normally fail to evaluate, but disabling
`_module.check` provides a sufficiently lazy evaluation to access the
wrapper options.
To prevent the `_module.check = false` module from leaking into user
configs, it has a unique module key and gets disabled inside the wrapper
modules (`wrappers/_shared.nix`).
Currently we represent `vim.diagnostic.config()` as a top-level
`diagnostics` option. This means we have no clear namespace for
(e.g.) `vim.diagnostic.<action>` keymap functions.
Moved `extraFiles` from `modules/output.nix` into its own file `modules/files.nix`.
Users should now assign text to a `text` attribute, however they could
also assign a file path to a `source` attribute instead.
The old method of directly assigning a string still works, and is
coerced to the new type along with a deprecation warning.
Let's simplify things by defining all modules in `./plugins`, `./modules`
and `./wrappers/modules`.
Instead of currying `pkgs` into a bootstrapping module, we can require
`defaultPkgs` be provided as a special arg.
This refactor allows us to completely remove `flake-modules/modules.nix`!
