TypeScript

After considering the differences between Flow and TypeScript 2.0 I’m thinking I’d like to try moving decaffeinate to TypeScript 2.0. @alangpierce’s comment is pretty spot-on in terms of where the two projects stand. There probably isn’t enough benefit to justify the switch purely on technical merit. However, both @alangpierce and I have been looking for an opportunity to dig deeper into TypeScript and using decaffeinate for that purpose seems reasonable.

Why?

• In my experience, my editor (WebStorm) has better support for TypeScript than for Flow.
• TypeScript has superior tooling, especially around bringing types in from the @types npm namespace and automatic generation of .d.ts files.
• Now that strictNullChecks is an option, my favorite feature from Flow is also in TypeScript (non-nullable types).
• Configuring babel is somewhat of a headache, and I really only ever use the es2015 preset plus a handful of things, all of which are supported by TypeScript.

Roadmap

• coffee-lex (https://github.com/decaffeinate/coffee-lex/pull/77)
  • remove .flowconfig
  • add tsconfig.json
  • rename sources to use .ts extension
  • configure rollup
  • fix type errors
  • ~emit types for dist files~ (https://github.com/rollup/rollup-plugin-typescript/issues/54)
  • refactor token types to use an enum (breaking change, assign explicit number values to prevent reordering issues)
  • remove coffee-lex.js.flow once all other projects are converted
• decaffeinate-parser
  • add tsconfig.json
  • rename sources to use .ts extension
  • configure rollup
  • fix type errors
• decaffeinate-traverse
  • remove .flowconfig
  • add tsconfig.json
  • rename sources to use .ts extension
  • configure rollup
  • fix type errors
• decaffeinate
  • remove .flowconfig
  • add tsconfig.json
  • rename sources to use .ts extension
  • configure rollup
  • fix type errors

I don’t want this to interfere with any of your work, @alangpierce, so I’ll try to do things in small chunks that are unlikely to cause problems.

[alangpierce]

The core decaffeinate project is 100% TypeScript now, so I’m going to call this a success and close the issue. Technically decaffeinate-traverse is still JavaScript, but it’s not used at the moment, so seems low priority. It also might be nice to move bulk-decaffeinate and decaffeinate-examples to TS eventually, but I’ll call that out of scope for now. Given that decaffeinate produces JavaScript, might be nice to have at least a little plain JavaScript. 😄

[alangpierce]

Yep, I’m sure @types/mocha is better, I’m certainly new to all this stuff. I’ll probably put up a PR for that this weekend.