@codincod/codemirror-lang-nix

This package implements Nix language support for the CodeMirror code editor, using the Lezer grammar Replit wrote for @replit/codemirror-lang-nix, with the parse fixes below on top of it.

Written in part for CodinCod, a competitive coding platform, where it colours the editor people solve puzzles in.

This code is released under an MIT license.

Usage

import { EditorView, basicSetup } from "codemirror"
import { nix } from "@codincod/codemirror-lang-nix"

const view = new EditorView({
  parent: document.body,
  doc: `{ lib, stdenv }:

stdenv.mkDerivation {
  pname = "hello";
  version = "2.12.1";

  meta = with lib; {
    license = licenses.gpl3Plus;
  };
}`,
  extensions: [basicSetup, nix()],
})

What changed

Five parse fixes over the published 6.0.1, each with grammar tests:

• the escapes of an indented string. ''$, ''' and ''\n each ended the string early, which broke every derivation carrying a shell script;
• a trailing comma in a formal argument set, which is how nixfmt writes one that spans lines;
• true, false, null, builtins and or as attribute and argument names, which Nix allows and the grammar did not;
• an inherit that names nothing, as in inherit (x);;
• ++ tokenizing as two +, which a rebuild with a current @lezer/generator otherwise reintroduces.

The same five sit on the upstream branch, without the comments, for a pull request to Replit.

Tests

npm test builds the parser and runs the grammar tests in test/*.txt.

npm run corpus <directory> parses every .nix file under a directory and reports how many produce no error node. Against nixpkgs 25.05, 31646 files, that is 99.99%. The two it does not read are a file nixpkgs keeps deliberately unparseable as a fixture for its own tests, and one path interpolation.

Known gaps

A path may interpolate, as in ./${name}/default.nix. A path is one token here, so that one reads as an error.