Automatically save updated `yarn.lock` file for dependabot PRs. This is necessary because dependabot doesn't support Yarn v2 yet.

dependabot-fix-web.yml

# Inspired by https://gist.github.com/amacneil/60bf679f357bad9d62103cfdc86cbd74
# Automatically save updated `yarn.lock` file for dependabot PRs.
# This is necessary because dependabot doesn't support Yarn v2 yet:
# https://github.com/dependabot/dependabot-core/issues/1297
#
# Note: We use the `pull_request_target` event due to GitHub security measures.
#       It is important to ensure we don't execute any untrusted PR code in this context.
# See: https://github.blog/changelog/2021-02-19-github-actions-workflows-triggered-by-dependabot-prs-will-run-with-read-only-permissions/
#      https://securitylab.github.com/research/github-actions-preventing-pwn-requests

name: Dependabot add web yarn.lock

on:
  pull_request_target:
    paths:
      - 'web/**'

jobs:
  build:
    name: fix
    runs-on: ubuntu-18.04
    if: |
      github.actor == 'dependabot[bot]' &&
      contains(github.event.pull_request.head.ref, 'dependabot/npm_and_yarn/')
    # IMPORTANT: setting YARN_ENABLE_SCRIPTS=false is critical to ensure that untrusted
    # PRs can't add an npm package and then use that to execute untrusted code in
    # a trusted context. See links at the top of this workflow for further details.
    # See also: https://github.com/yarnpkg/berry/issues/1679#issuecomment-669937860
    env:
      YARN_ENABLE_SCRIPTS: false
      YARN_ENABLE_IMMUTABLE_INSTALLS: false

    steps:
      - uses: actions/checkout@v2
        with:
          # Using a Personal Access Token here is required to trigger workflows on our new commit.
          # The default GitHub token doesn't trigger any workflows.
          # See: https://github.community/t/push-from-action-does-not-trigger-subsequent-action/16854/2
          token: ${{ secrets.REPO_ACCESS_TOKEN }}
          ref: ${{ github.event.pull_request.head.ref }}
          # Need fetch-depth in order to soft reset the most recent commit.
          fetch-depth: 2

      - uses: actions/setup-node@v2
        with:
          node-version: '14.17'
      
      # Undo yarn.lock changes from last commit (if any), run yarn install,
      # and add/commit any yarn.lock changes. Dependabot will commit an invalid
      # yarn.lock file for dependecy changes in the root package.json. `yarn install`
      # will not work with an invalid yarn.lock file.
      - name: Install and commit yarn.lock
        working-directory: ./web
        run: |
          git config user.name "[name]"
          git config user.email "[email]"
          git reset --soft HEAD~1
          git restore --staged yarn.lock
          git checkout -- yarn.lock
          yarn install
          git add yarn.lock
          git commit -m '${{ github.event.pull_request.title }}'
          git push -f