TypeScript 3.8 Iteration Plan

This document outlines our focused tasks for TypeScript 3.8, 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

TypeScript 3.8

Work Items

Expected Work Items

Compiler Features
Performance
Command Line Tooling
- downlevel-dts
Editor Productivity
- Investigate performance improvements
  - Cross-file Go-To-Definition Fixes
  - Investigate requesting refactorings less often
- Migration tooling investigation: Elicit feedback on…
  - Editor-Triggered .ts to .js Refactorings
  - Editor-Triggered Suggestions on Introducing a .ts File
- Refactorings
- Quick Fixes
  - Add declare Modifier to Class Property
- Call Hierarchy API
Infrastructure
- JIT deoptimization analysis
  - Find common deopts and fix them
- Performance Diffs on PRs
- GitHub Package Registry Publishing for @types.
- Pull Request Debt
- TSServer Crash Dump Infrastructure
Documentation

Deferred Work Items

Interactive diagnostics

Planning Meeting Notes

Motivations

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

Notes

Compiler Features
- New Export Forms
- Top-Level Await
- Private Fields (Flagged?)
- Address anticipated feedback from 3.7
- Lib Updates?
- Declaration emit
  - UX
  - Performance
- Bug Squashing!
  - Debt reduction for addressing bugs
  - Awareness of release
Performance
- Investigate async file-writing
- Plugin Investigation: async plugins?
- Declaration emit
- updateGraph details in TSServer responses
  - Provides easier analysis for TSServer performance problems.
  - Requires synchronization with editor teams.
- Investigate recompilation speed
  - tsc --watch isn’t as fast as gulp-tsb (because it’s less accurate). Is there a fast and loose mode?
Tooling
- dts-downlevel
  - Several library authors have explained that it is hard to support older versions of TypeScript while using the latest.
  - .d.ts files keep artifacts of your version of TS even when “uninteresting” for older versions of TS.
  - Goes back to long-standing request (e.g. readonly properties broke earlier versions of TS)
  - Enabled by typesVersions
- Editor Productivity
  - Interactive diagnostics ❌
    - Probably won’t be able to prioritize during this release.
  - Investigate performance improvements
    - Cross-file go-to-definition
      - Noticed in partner team codebases
    - Request refactorings less often
  - Investigate automatic editor migrations
    - Do existing tools solve the problem?
    - Can we do a good job in the editor?
      - CD & App building
  - Leave room open to refactoring discoverability and triggers.
    - Refactorings without spans might need to be triggerable.
  - Refactorings
    - Extract to constant should come first.
    - Refactoring for convert to template string.
Infrastructure
- Triage & Scheduling
- Weekly Status Mails for Bug Reduction
- JIT deoptimization analysis
  - VS Code extension
  - CI integration (e.g. @typescript-bot what deoptimizes?)
    - Will be learning here from general perf investigations. Not certain if this will be useful.
- extendedDiagnostics diffs on PRs
- GitHub Package Registry publishing for @types.
- Expand version list for crash dumps
  - We should be looking at beta and RC.
Documentation
- Handbook
- Website
- Contributing Guidelines

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