Yarn Target Determinator

A GitHub Action that determines a list of Yarn 2 workspaces to test using an input list of changed files.

Overview

This action determines a list of Yarn 2 workspaces that need to be tested based on an input list of changed files. It'll return a list containing the workspaces that changed, as well as which other workspaces depend on the changed workspaces, and so on. It's best used alongside https://github.com/jitterbit/get-changed-files.

This action makes a couple assumptions:

• You're using Yarn 2 with a single worktree at the root of your repo.
• All package.json files in your repo are for workspaces that are members of the root worktree.

PRs to lift these restrictions are welcome.

Example

Imagine a Yarn 2 monorepo with two workspaces frontend and backend that depend on a third workspace common. If somebody opens a PR that changes just the frontend workspace, the workflow below will run the test job on only frontend.

If another PR touches files in common. the workflow below will understand the dependency tree and run the test job on common, frontend, and backend.

As more workspaces are added to your monorepo, this action will continue to determine targets accurately without any manual reconfiguration.

name: CI

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  target-determinator:
    runs-on: ubuntu-20.04
    outputs:
      targets: ${{ steps.set-targets.outputs.targets }}
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v1
      - id: get-changed-files
        uses: jitterbit/get-changed-files@v1
        with:
          format: json
      - id: target-determinator
        uses: sargunv/yarn-target-determinator@v1
        with:
          files: ${{ steps.get-changed-files.outputs.all }}
      - id: set-targets
        run: echo '::set-output name=targets::${{ steps.target-determinator.outputs.targets }}'

  test:
    runs-on: ubuntu-20.04
    needs: [target-determinator]
    strategy:
      fail-fast: false
      matrix:
        target: ${{ fromJson(needs.target-determinator.outputs.targets) }}
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-node@v1
      - run: yarn workspaces focus ${{ matrix.target }}
      - run: yarn workspace ${{ matrix.target }} run test

Inputs and outputs

inputs:
  files:
    description: The list of all changed files to validate, encoded as a JSON array
    required: true

outputs:
  targets:
    description: The list of Yarn workspaces to test, encoded as a JSON array