TypeScript 5.4 Iteration Plan

[DanielRosenwasser]

This document outlines our focused tasks for TypeScript 5.4. 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
2023-11-20	TypeScript 5.3 Release
2024-01-19	Create 5.4 Beta (5.4.0) Build for Testing
2024-01-23	TypeScript 5.4 Beta Release
2024-02-16	Create 5.4 RC (5.4.1) Build for Testing
2024-02-20	TypeScript 5.4 RC Release
2024-03-01	Create 5.4 Final (5.4.2) Build for Testing
2024-03-05	TypeScript 5.4 Final Release 🚀

gantt
    dateFormat  YYYY-MM-DD
    TypeScript 5.3 Stabilization Period : 2023-11-03, 2023-11-20
    TypeScript 5.4 Beta Development : 2023-11-03, 2024-01-19
    TypeScript 5.4 RC Development : 2024-01-20, 2024-02-16
    TypeScript 5.4 Stabilization Period : 2024-02-16, 2024-03-05
todayMarker stroke-width:5px,stroke:#0f0,opacity:0.5

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Compiler and Language

• Type Narrowing for Variables in Closures Occurring After Last Assignments
• The NoInfer Intrinsic
• Isolated Declarations
• Investigate --module preserveand require() in --moduleResolution bundler
• Investigate and Review Regex Syntax Validation
• Checks for Never-Initialized Variables
• Champion throw Expressions
• Investigate Function Implementations Returning Indexed Access and Conditional Types
• Make isTypeAssignableTo public on TypeChecker #56448
• Alleviating Pain-Points around dual-ESM/CJS-published Packages
• Investigate Syntactic Variance Measurement
• Symbol Visibility Walk Optimizations for .d.ts Emit
• Communicate out Plan for 5.0 Deprecations in Anticipation of 5.5

Editor and Language Service

• Define Initial Sketch of LSP Support
• TSServer File-Watching Events
• Organize Imports Respecting type Imports
• Investigate AI-powered Refactorings

Performance

• Investigate Running With V8 Snapshots
• Parallelization Experimentation

Website and Docs

• Author and Iterate on Module Documentation
• Simplify and Refactor Website for Faster Builds

Infrastructure

• Expand Performance Suite
• Move DefinitelyTyped to GitHub Actions
• DefinitelyTyped Monorepo Improvements
• arethetypeswrong validation in DefinitelyTyped

[DanielRosenwasser]

You can see the previous iteration plan for 5.3 here.

[JoshuaKGoldberg]

• Make isTypeAssignableTo public on TypeChecker #56448

This is one of the most exciting release points for us in typescript-eslint in a long time. Very high benefit here. Very much hoping there's no last-minute issue discovered. Thank you! 🙌

[zaguiini]

Define Initial Sketch of LSP Support

It's not clear to me what this means. I thought TSC already was LSP-compliant?

[jakebailey]

tsserver uses the tsserver protocol, which predates LSP. It does not (yet) implement LSP.

[guillaumebrunerie]

tsserver uses the tsserver protocol, which predates LSP. It does not (yet) implement LSP.

I've been using https://github.com/typescript-language-server/typescript-language-server#readme (a LSP implementation for TypeScript wrapping tsserver) with Emacs for quite some time and it works perfectly well, but I've never used tsserver directly so I'm not sure if there are any features that I'm missing.

Would a native implementation of LSP have any user-visible consequences, compared to using a wrapper like this one? Or is it mostly about supporting LSP officially and removing the need for a third-party wrapper?

[jakebailey]

Would a native implementation of LSP have any user-visible consequences, compared to using a wrapper like this one? Or is it mostly about supporting LSP officially and removing the need for a third-party wrapper?

The latter, though there are of course other benefits.

[jfet97]

I'll share a link to Reverse mapped types with intersection constraint as well 😛, both for its enabling of type inference and Excess Property Checking together, and for doing some advertising for reverse mapped types, making @Andarist happy.

[DanielRosenwasser]

@typescript-bot create release-5.4

[typescript-bot]

Heya @DanielRosenwasser, I've started to create the release-5.4 branch for you. Here's the link to my best guess at the log.

[DanielRosenwasser]

Jake says he fixed the build.

@typescript-bot create release-5.4

[typescript-bot]

Heya @DanielRosenwasser, I've started to create the release-5.4 branch for you. Here's the link to my best guess at the log.