Contributing Guide

Relevant source files

This document explains how to contribute code changes to the TypeScript compiler and language service codebase. It covers setting up your development environment, the build and test workflow, writing tests, managing baselines, and submitting pull requests. For information about reporting issues, see Issue Reporting. For details about the build system itself, see Build System. For testing infrastructure details, see Test Infrastructure.

Important: Development in this codebase is winding down per CONTRIBUTING.md5 All code changes should be submitted to the https://github.com/microsoft/typescript-go repository. PRs to this repo will only be merged for critical 6.0 issues, such as security issues or serious regressions README.md31-38

Prerequisites and Environment Setup

Required Tools

Before contributing, you need the following installed on your machine:

Tool	Purpose	Installation
Node.js	JavaScript runtime (>=14.17)	package.json29 Download from https://nodejs.org
Git	Version control	Standard installation
hereby	Task runner for building and testing	`npm install -g hereby` CONTRIBUTING.md87
Editor	Code editing (VS Code recommended)	https://code.visualstudio.com

Additional requirements:

A GitHub account for forking and creating pull requests CONTRIBUTING.md83
Contributor License Agreement (CLA) signing upon first PR CONTRIBUTING.md134-136

Git Configuration

For Windows users, enable long path support before cloning:

To avoid line ending issues, configure Git:

Sources: CONTRIBUTING.md109-111 CONTRIBUTING.md148 package.json29-30

Development Environment Setup Workflow

Sources: CONTRIBUTING.md89-107 package.json100-101

Build and Development Workflow

Core hereby Tasks

The hereby command-line tool, defined in Herebyfile.mjs9 orchestrates all build and test operations. Common tasks:

Command	Purpose
`hereby local`	Build compiler to `built/local/` Herebyfile.mjs246
`hereby clean`	Delete build artifacts Herebyfile.mjs518
`hereby LKG`	Update Last Known Good compiler in `lib/` Herebyfile.mjs540
`hereby tests`	Build test infrastructure Herebyfile.mjs410
`hereby runtests`	Run tests with built compiler Herebyfile.mjs421
`hereby runtests-parallel`	Run tests across multiple threads Herebyfile.mjs433
`hereby baseline-accept`	Accept baseline test results Herebyfile.mjs478
`hereby lint`	Run ESLint on TypeScript source Herebyfile.mjs491

Sources: Herebyfile.mjs45-550 package.json88-101

Development Workflow Diagram

Sources: CONTRIBUTING.md113-115 package.json91-101 Herebyfile.mjs421-489

Writing and Running Tests

Test Organization

Tests are categorized by their target functionality:

Directory	Purpose
`tests/cases/compiler/`	General compiler tests
`tests/cases/conformance/`	Language specification compliance tests
`tests/cases/fourslash/`	Language service (IDE) tests
`tests/cases/projects/`	Multi-file project build tests

Sources: CONTRIBUTING.md216-227

Adding a New Test

For details on test case structure and syntax, see Writing Tests.

Create a .ts file in the appropriate directory.
Run the specific test using the --tests flag:

Sources: CONTRIBUTING.md216-228 scripts/build/tests.mjs36

Baseline Testing System

TypeScript uses a "baseline" system where compiler output is compared against reference files.

Baseline Type	Location	Content
Local	`tests/baselines/local/`	Output from the current run scripts/build/tests.mjs22
Reference	`tests/baselines/reference/`	Known good output scripts/build/tests.mjs23

Baseline Workflow

Sources: CONTRIBUTING.md244-270 scripts/build/tests.mjs22-23 Herebyfile.mjs478-489

Pull Request Process

Submission Criteria

Before submitting a Pull Request (PR):

Ensure you have an associated issue in the "Backlog" milestone CONTRIBUTING.md117-119
Verify that hereby runtests-parallel passes locally package.json89
Include baseline changes in the commit CONTRIBUTING.md267-270
Disclose if AI assistance was used for the patch CONTRIBUTING.md9

For the complete PR lifecycle and review expectations, see Pull Request Process.

Sources: CONTRIBUTING.md7-17 CONTRIBUTING.md138-153