TypeScript 3.5 Iteration Plan

[DanielRosenwasser]

This document outlines our focused tasks for TypeScript 3.5, as well as some of the discussion that explains how/why we prioritized certain work items. Nothing is set in stone, but we will strive to complete them in a reasonable timeframe.

Dates

Here's the release plan.

1. May 10th: Create a release-3.5 branch, and update the version to 3.5.0-rc. master is locked from receiving new feature-work that is not 3.5-bound.
   1. Start a build of TypeScript for Visual Studio for our remote testing team.
2. May 15th: Last day to adjust the release-3.5 branch with any feedback we receive.
   1. Kick off a final Visual Studio build if necessary.
   2. (2pm Pacific) Produce an insiders release for VS Code.
3. Morning of May 16th: The release candidate goes out.
4. May 24th: Merge master into release-3.5 one last time, finalize the version as 3.5.1. master is unlocked. Critical changes for 3.5 must be ported in.
   1. Start a build of TypeScript for Visual Studio for our remote testing team.
5. May 29th: Last day to adjust the release-3.5 branch with any feedback we receive.
   1. Kick off a final Visual Studio build if necessary.
   2. (2pm Pacific) Produce an insiders release for VS Code which is identical to the final release.
6. May 30th: Announcing TypeScript 3.5 🚀

Work Items

Expected Work Items

• Language
  • Investigate negated types 🏃🏻‍
  • globalThis expressivity fixes
  • Strongly typed iterators and generators
• Compiler
  • Anticipated --incremental fixes and improvements
  • --declaration and --allowJs
  • --declaration and --isolatedModules
  • APIs for --incremental and composite projects (--build mode) 🏃
  • Investigate TypeScript plugin APIs 🏃
• Language Service
  • Smart Select API
  • Sorted/prioritized completions
  • Extract type
• Infrastructure
  • Automated testing infrastructure for language service on real world code 🏃🏻‍
  • Migrate to ESLint 🏃🏻‍

(🏃🏻‍ means work has already started)

Deferred Work Items

• Arbitrary index signatures
• Call hierarchy

---

Planning Meeting Notes

Motivations

• Goals and current 6-month roadmap
• GitHub user feedback (👍s)
• Feedback from customer interviews and social media.
• Visual Studio and Visual Studio Code feedback and new functionality demands
• Actionable PRs (need to make a call)
• Bug backlog

General (compiler/infrastructure/reliability)

• Negated types

  • Rationale: Core type system
  • Uses: control flow analysis on generic/"higher order" types
  • Problems: But you end up with lots of vacuous intersections that are "garbage" types.
  • Will likely lead to a tail of bugs, at least initially
  • Action item: need to prototype, see what sort of breakage we see with implementations of integration with control-flow analysis, and see what the perf impact is.
  • ✅ Work on this.

• Arbitrary index signatures

  • Rationale: Core type system
  • Not a must for negated types
  • But like to get them done first.
  • Also need a unifying concept between them and mapped object types.
  • Resolution: Defer

• Compiler API prototyping

  • Rationale: minification, 3rd party tools integration
  • In progress
  • ✅

• Expecting --incremental build issues

  • Rationale: Stability, scaling, performance
  • ✅

• Crawler work for testing TSServer

  • Rationale: Stability
  • Context:
    • IntelliCode team crawls public code to train on, but leverages TSServer.
    • Turns out that it was a great way to test TSServer and catch bugs!
    • We want to leverage it to get a good litmus that it's stable.
    • Give partner teams assurance that they can adopt nightly TypeScripts.
  • ✅

• TSLint -> ESLint migration

  • Internal engineering
  • ✅

• New engineer starting!

  • Ramping-up bugs
  • Website
    • Education and UX
  • ✅

• globalThis-related work

  • Bug and standards involvement
  • Issues with block-scoped declarations interfacing with the global object.
  • ✅

• --declaration with --allowJs

  • TypeScript beyond TypeScript
  • ✅ 🎉

• --declaration with --isolatedModules

  • User demand
  • Aside: Ensure this all works with composite.
  • Resolution: investigate

Productivity

• Smart Select API
  • TSServer: Smart select API #29071
  • VS Code ask, but generally applicable editor integration
  • ✅
• Sorted/prioritized completions
  • favor local types and values in autocomplete popup over ambients declaration #15024
  • Editor quality improvements
  • This and smart select have been around for long enough that they get priority.
  • ✅
• Extract type refactoring
  • Suggestion: Refactor extract to type alias/typedef #23869
  • Shouldn't it just always work?
    • <T>(x: T): { value: T }
    • It has all the same problems as extract method!
      • Well you don't have to worry about control flow.
  • Could just do this for non-generic types for the minimal-viable product (MVP).
  • Resolution: try to get done for 3.5. ✅
• Call hierarchy breadcrumbs
  • Feature request: Call Hierarchy vscode#16110
  • VS Code ask, but generally applicable editor integration
  • Resolution: Probably will defer to next version.

[EisenbergEffect]

@DanielRosenwasser Thanks for being so transparent with the plans. It was way cool to read the 3.4 release announcement and then pop over here to see that you already have pretty developed plans for the next iteration.

Go TypeScript team!

[kirillgroshkov]

Amazing work guys!

[ExE-Boss]

I’d like to see #30586 fixed.

Preferably in some way that isn’t just a band‑aid.

[xiaoxiangmoe]

What's TypeScript plugin API? Does this affect babel-plugin-transform-typescript users?

[mrmckeb]

Is it possible to be involved in testing for "Investigate TypeScript plugin APIs"?

I'd love to have typescript-plugin-css-modules available during build time. I'm currently in the process of reworking it a little, so please let me know.

[Yaojian]

I'd like to see #21592 fixed.

It force me to stuck with TypeScript 3.1.6 😢(the only version without this bug among TS 3.x)