update-pr-description.yml

name: Update PR Description

on:
  pull_request:
    types: [opened, synchronize]

jobs:
  update-description:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@v2
        with:
          ref: ${{ github.event.pull_request.head.sha }}
      - name: Add PR base ref
        # Fetch the ref of the base branch, just the single commit.
        run: git fetch --depth=1 origin +refs/heads/${{github.base_ref}}:refs/remotes/origin/${{github.base_ref}}
      - name: Track PR base branch
        # Turn the just-fetched ref into a local branch.
        run: git branch --track ${{github.base_ref}} origin/${{github.base_ref}}
      - name: Fetch commits in-between base and HEAD
        # While the ancestor commit between HEAD and the branch base isn't in the local tree
        # fetch X more parent commits of the branch base and branch head.
        run: |
          while [ -z $( git merge-base ${{github.base_ref}} HEAD ) ]; do
            git fetch --deepen=10 origin ${{github.base_ref}} HEAD;
          done
        # Sets the commit SHAs of head and branch base into two environment variables
        # that `nx affected` will read from.
      - name: Derive SHAs for base and head for `nx affected` commands
        uses: nrwl/nx-set-shas@v2
        with:
          main-branch-name: ${{github.base_ref}}