plugins/conform-nvim: automatically install formatters

[saygo-png]

Closes #1141

This PR tries to automatically install the needed packages for Conform formatters.
It extracts formatters names from the settings.formatters_by_ft option. Then for each name
it searches for a corresponding package in 4 attribute sets, in order of priority

1. User overrides
2. Manually written special cases
3. Auto generated defaults
4. Custom formatters (all set to null)

A user can choose what package a formatter should install, especially useful for versioned formatters like for python 3.12 or 3.13. Since this value can be null, they can also make a formatter not install anything.

The automatic package attrset right now is created with pkgs.${conform-name}. More advanced logic could be added, such as replacing all _ with - and checking if that exists in nixpkgs. But i choose against this since it would only cut down the manual list by a few entries but would add a lot of hard to predict behavior. The current simple defaulting mechanism cuts the manual list in about half.

The test right now is very simple. Upstream has each formatter in its own file with a name identical to the Conform name. So I just list that directory of the nix derivation for the plugin, remove .nix and generate a Nix list of strings.
To prevent IFD this is generated with CI. Then I just create a Nixvim config with every supported formatter in Conform.

Limitations of this approach:

1. There could be a Conform formatter "foo" that matches nixpkgs pkgs.foo. But the formatter expects executable foofmt meanwhile the nixpkg does not contain it. This will not be caught as an error in the test.
2. It could also be the case that Conform formatter "foo" matches pkgs.foo AND contains an executable with the same name, but it actually is a totally different executable and package, just with incidentally matching names.

I think one could write a more extensive test that covers 1 using Lua but i'm not good enough with Lua to do that.

There is no test for the override functionality or one that checks if custom formatters' packages are getting set to null
This is because I have no clue how to write that. I'd have to eval those options first, read them, and assert that some predicates hold. For example for the nulling i'd imagine I would read the customFormatters attrset, get the values with lib.attrValues and assert that everything is null. If someone could point me to how to achieve that I could write those tests.

[saygo-png]

Almost forgot about this:
The example for the overrides option does not render properly in the docs. The issue is with the python package. How do I add that properly? I know i can brute force it with just a plain string but is there no way to make this package render nicely without turning the entire example into a string?

[saygo-png]

Just found issue #2412
This pr is not as ready as I thought. I'm gonna change the behavior for unpackaged formatters. I'll send a warning if a user declares a formatter that isn't packaged.

[saygo-png]

I've added warnings for packages that do not get installed, they look like this:

evaluation warning: Nixvim (conform-nvim): You have enabled the 'blue' formatter that relies on a package marked 'unpackaged'.
                    Because of that it will not be installed. To disable this warning, explicitly disable installing the package
                    by setting the 'conform-nvim.autoInstall.overrides.blue' option to 'null'. You can also disable
                    all warnings related to packages not installed by autoInstall with 'conform-nvim.autoInstall.enableWarnings'.

I did a small refactor of the generate.nix script to make it easier to add more JSON generated files.

I think the code for this looks like a bit of a disaster but it does work and I couldn't come up with a cleaner implementation. It would look better in Haskell with algebraic data types and pattern matching :).

[MattSturgeon]

It would look better in Haskell with algebraic data types and pattern matching :).

Just for the record, the generate scripts can technically be in any language. We commonly use bash either at buildtime (runCommand) or at runtime (writeShellApplication, writeShellScriptBin), sometimes we also use python scripts. However, the language chosen should be one that @nix-community/nixvim-committers are comfortable with; we're probably not ready for haskell just yet, but I'd personally love to learn at some point™ 😁

[MattSturgeon]

Nits, tips, suggestions. Feel free to discuss, dismiss, implement as you see fit.

The overall diff SGTM. Thanks for another great contribution!

[saygo-png]

Just for the record, the generate scripts can technically be in any language.

Sorry I was unclear; I meant the Nix code for the plugin which obviously is staying Nix.

[MattSturgeon]

LGTM, thanks for another great contribution!

[khaneliman]

Thanks for doing this, I meant to do it a long time ago!

Seems to work fine for most formatters. For some reason, I get a lua error trying to use ConformInfo when letting csharpier get auto installed. But, if I leave my manual configuration of the pkg mapping in formatters.*.command it is fine.

[MattSturgeon]

But, if I leave my manual configuration of the pkg mapping in formatters.*.command it is fine.

Would that make for a suitable example (in a followup PR)?

[GaetanLepage]

Well done @saygo-png!

[saygo-png]

@khaneliman The csharpier issue is an upstream issue with conform-nvim stevearc/conform.nvim#699 not this PR

[khaneliman]

@khaneliman The csharpier issue is an upstream issue with conform-nvim stevearc/conform.nvim#699 not this PR

Looks like someone created a PR for it, too. Thanks for identifying it. stevearc/conform.nvim#772