TypeScript 4.9 Iteration Plan

[DanielRosenwasser]

This document outlines our focused tasks for TypeScript 4.9. It minimally indicates intent to investigate tasks or contribute to an implementation. Nothing is set in stone, but we will strive to complete these tasks in a reasonable timeframe.

Date	Event
August 23rd	TypeScript 4.8 Release
September 16th	Create 4.9 Beta (4.9.1) Build for Testing
September 20th	TypeScript 4.9 Beta Release
October 28th	Create 4.9 RC (4.9.2) Build for Testing
November 1st	TypeScript 4.9 RC Release
November 11th	Create 4.9 Final (4.9.3) Build for Testing
November 15th	TypeScript 4.9 Final Release 🚀

gantt
    dateFormat  YYYY-MM-DD
    TypeScript 4.8 Stabilization Period : 2022-08-05, 2022-08-25
    TypeScript 4.9 Beta Development : 2022-08-05, 2022-09-16
    TypeScript 4.9 RC Development : 2022-09-16, 2022-10-28
    TypeScript 4.9 Stabilization Period : 2022-10-28, 2022-11-15
todayMarker stroke-width:5px,stroke:#0f0,opacity:0.5

Language and Compiler Features

• ECMAScript Decorators
• Contextually Typed And Compatible Operator
• lib.d.ts Updates
• Support .ts as a Module Specifier for Bundler/Loader Scenarios
• Investigate Fine-Granularity Module Resolution Options
• Investigate Per-File Settings
• Make @types/web Versionable
• Investigate --isolatedDeclaration Emit Mode

Editor Productivity

• Switch to FsEvents for File-Watching by Default
• Virtual File System Support in TSServer
• Investigate Cancellation in Browser Contexts
• Prototype Automatic Type Acquisition in Web Contexts
• Investigate TS Server Plugins on the Web
• High Confidence JavaScript Diagnostics in Classes
• Provide Walkthroughs in Visual Studio Code Welcome View
• Easy Run/Debug for Loose TypeScript Files

Performance

• Investigate Module Resolution Caching in .tsbuildinfo Files
• Investigate Tooling for JIT Deoptimizations
• Investigate Outstanding Performance Issues
• Enrich TS Server Tracepoints

Infrastructure

• Enable strictFunctionTypes on TypeScript Codebase
• Determining Module Migration and Shipping Strategy
• Rewrite TSServer Crawler
• TSServer Performance Testing Infrastructure

Website

• Accessibility Improvements
• Make Onboarding and Cross-Platform Installation Smoother

[DanielRosenwasser]

Previous iteration plan is over at #49074

[DanielRosenwasser]

Looks like we may be adjusting the beta deadline to early next week to get in a few PRs that needed to wait as a result of 4.8 servicing tasks.

[DanielRosenwasser]

@typescript-bot create release-4.9

[typescript-bot]

Heya @DanielRosenwasser, I've started to create the release-4.9 branch for you. Here's the link to my best guess at the log.

[DanielRosenwasser]

A few updates:

• While decorators have reached stage 3, we saw some behavior in the spec that needed to be discussed with the champions. Between addressing that and reviewing the changes, we expect decorators will be implemented in the next version.
• Rather than shipping pieces of module resolution, we'd like to have a cohesive story on each of the above. That will likely be going to the next version as well.
• Caching in .tsbuildinfo files is still in flux. We'll likely have to decide on that only if we feel like we can get sufficient coverage.

[DanielRosenwasser]

@typescript-bot create release-4.9

[typescript-bot]

Heya @DanielRosenwasser, I've started to create the release-4.9 branch for you. Here's the link to my best guess at the log.

[DanielRosenwasser]

@typescript-bot sync release-4.9

[typescript-bot]

Heya @DanielRosenwasser, I've started to sync release-4.9 with main for you. Here's the link to my best guess at the log.

[DanielRosenwasser]

Due to #50927, the correct beta on npm is 4.9.1-beta. The RC will be 4.9.2-rc. The stable will be 4.9.3.

One day we will be able to avoid incrementing the patch and just publish pre-releases.

[fatcerberus]

I always thought it was weird that TS prereleases consume entire version numbers. What is the technical reason for that?

[jakebailey]

Something to do with places like the VS Marketplace which don't support prerelease tags, though that might have changed entirely. https://github.com/microsoft/TypeScript/wiki/TypeScript's-Release-Process#why-do-you-need-to-set-the-patch-version-on-pre-releases

Maybe things have changed enough such that we can do something different now.

[xiaoxiangmoe]

Will per-file settings available in ts 4.9? Or maybe move it to 5.0?

[chriskrycho]

👋🏼 In Ember.js' testing against TS, we noted failures against 4.9 starting with the 4.9.0-dev.20221014 release. I believe these are legitimate issues (the fix here is demonstrably all sorts of unsafe!), but the underlying change wasn't called out in the 4.9 blog post, so I wanted to flag it here as a thing to possibly mention – I assume this was a case of intersection handling and unknown getting better.

[DanielRosenwasser]

@typescript-bot sync release-4.9

[typescript-bot]

Heya @DanielRosenwasser, I've started to sync release-4.9 with main for you. Here's the link to my best guess at the log.

[jakebailey]

I feel like we need to add -X theirs to that workflow's merge so that it always takes what's in main (kinda like reset --hard main but without breaking history). Unfortunate that we hit conflicts thanks to LKG changing in both.

[DanielRosenwasser]

The 5.0 iteration plan is over at #51362.

[DanielRosenwasser]

@typescript-bot bump release-4.9

[typescript-bot]

Heya @DanielRosenwasser, I've started to update the version number on release-4.9 to 4.9.4 for you. Here's the link to my best guess at the log.