checkout@v2 doesn't allow `git diff origin/master`

Hi, I have such a step in my actions config:

    name: Get list of changed files
    id: changed_files
    run: |
        list=`git diff --name-only origin/master HEAD`
        echo $list
        echo "::set-output name=list::$list"
    shell: bash

When using checkout@v1 it works, while with checkout@v2 I get

fatal: ambiguous argument 'origin/master': unknown revision or path not in the working tree.

[ljharb]

ah sorry, i assumed you were a maintainer.

I don’t think it’s something we can configure; i think it’s something that the checkout action would have to do, by first making a call to the github API, to figure out the requisite fetch depth.

[JohnStarich]

This worked for me:

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v3
    - name: checkout
      run: |
        commits=${{ github.event.pull_request.commits }}
        if [[ -n "$commits" ]]; then
          # Prepare enough depth for diffs with master
          git fetch --depth="$(( commits + 1 ))"
        fi

For some actions, the diff is a rich source for data analyses. While this works, I’d love a built-in option (or default) to fetch the current PR’s history.