With Bun

Moonrepo with Bun

Overview

Use this skill to apply the moon Bun handbook defaults correctly.

Core principle: Bun support in moon is explicit opt-in. Enable both javascript and bun toolchains, and configure JavaScript to use Bun as package manager.

When to Use

• Adding Bun to a moonrepo.
• Fixing inconsistent runtime behavior across dev/CI.
• Standardizing project/task commands on bun/bunx.
• Migrating from package.json scripts to moon tasks.

Do not use as-is if your repo intentionally standardizes on Node runtime.

Canonical Setup

1) Enable Bun in .moon/toolchains.yml

javascript:
  packageManager: 'bun'

bun: {}

2) Pin Bun version for deterministic environments

bun:
  version: '1.0.0'

Alternative pinning path:

# .prototools
bun = "1.0.0"

3) Set project/task toolchains when needed

moon may default to Node in ambiguous scenarios. Force Bun for project/task execution when required:

# moon.yml
toolchains:
  default: ['javascript', 'bun']

tasks:
  build:
    command: 'webpack'
    toolchains: ['javascript', 'bun']

Important caveat: explicit task/project toolchains are primarily needed when executing node_modules binaries in ambiguous runtime contexts. Running the bun binary itself already implies Bun runtime.

Task Patterns

Prefer explicit Bun commands in tasks:

tasks:
  test:
    command: 'bun test'
  typecheck:
    command: 'bunx tsc --noEmit'
  build:
    command: 'bunx tsc -p tsconfig.build.json'

Migration Option

For short-term migration/prototyping, moon can infer tasks from package.json scripts:

javascript:
  inferTasksFromScripts: true

If your repo policy forbids package scripts, treat this as temporary bootstrap only.

What Bun Enablement Gives You

• Auto dependency install when package.json/lockfile changes.
• Workspace-aware install location handling.
• Project relationship discovery via dependencies, devDependencies, and peerDependencies.

Verification Checklist

• moon toolchain info javascript
• moon toolchain info bun
• moon query projects
• moon query tasks <project>
• Run one Bun-backed task: moon run <project>:typecheck

Common Mistakes

• Enabling bun.version but forgetting javascript.packageManager: bun.
• Assuming moon will always infer Bun from package.json.
• Mixing npm/pnpm/yarn commands in Bun-designated tasks.
• Treating inferred scripts as permanent task strategy.

Scope Note

The Bun handbook is intentionally compact. For repository structure, dependency management, and broader JavaScript guidance, apply the Node.js handbook patterns as compatible with Bun.