Proposal: Ecosystem: Babel plugin?

[edemaine]

I'm no expert on Babel, but I saw this comment by @ArmorDarks:

I think this won't be an issue at all if CS could be transpiled through Babel. Really, this is one of reason we're leaving CS — it is so damn hard to integrate into nowadays JS pipelines.

Is it feasible / interesting to make CoffeeScript 2 into a Babel syntax plugin?

[rattrayalex]

tl;dr, no, not really.

The CoffeeScript compiler doesn't produce a clean, babel-compatible AST. You could dig into the CS internals, parse out the AST, write a translator that makes it babel compatible, and wrap that in a babel plugin. That sounds pretty hard to me, and I wouldn't be surprised if there were basically unresolvable ambiguities.

Probably the easiest way would be to parse CS entirely into JS, re-parse it into a babel AST, and use that in the babel plugin. It'd be slow, and the sourcemaps would be worthless, but it'd save a build step.

[ArmorDarks]

Probably the easiest way would be to parse CS entirely into JS, re-parse it into a babel AST, and use that in the babel plugin. It'd be slow, and the sourcemaps would be worthless, but it'd save a build step.

Wow, that sounds already painful.

[itsMapleLeaf]

That's somewhat of a bummer. One of the reasons I'm hesitant to use CS2 is because of the need for an additional build step on unsupported ES6 environments.

[rattrayalex]

fwiw, I built LightScript from the ground up around Babel; you might give it a try. I'd be eager for feedback over on gitter

[edemaine]

Yes, I was imagining the CS → JS → reparsing as being simple and possible. It's exactly what we're currently doing in CS2 with coffee -c + babel transpilation, right? Wouldn't this still make it easier to use CoffeeScript in existing JS infrastructure as "just another plugin" to Babel?

[rattrayalex]

Worth keeping in mind that babel only processes .js etc by default; you'll have to pass a command-line argument in every time to process extensions too (see babel/babel#3741). eg; babel src -x .coffee --out-dir dist with plugins: ["coffeescript"] in the babelrc. Still more convenient than two-step build, but not seamless.

That said, here's roughly how I'd do it:

import { compile } from 'coffeescript'
import { parse } from 'babylon'

export default function (babel) {
  return {
    manipulateOptions(opts, parserOpts, file) {
      // don't process .js files
      // (this would need to be refined)
      if (file.opts.filename.endsWith('.js')) return;

      opts.parserOpts.parser = (input, options) => {
        const jsFromCoffee = compile(input);
        return parse(jsFromCoffee, options);
      };
    }
  }
}

I haven't tried it, treat that as pseudocode, but happy to help if anyone decides to give it a shot

[GeoffreyBooth]

This strikes me as a great idea. I don’t think the current compiler should be converted into a Babel plugin, but a Babel plugin that imports it like @rattrayalex’s example would surely make things more convenient for many people. On a current project I use Browserify to merge together .js files and .coffee files in the same project; the more ways to do the same thing, the better.

[GeoffreyBooth]

See #92 for more discussion of these issues.

[coffeescriptbot]

Migrated to jashkenas/coffeescript#4969