GitHub Actions: how to build a pull request as if it were merged?

Question

I\'m very excited about GitHub Actions.

I use Travis-CI and AppVeyor now, which have \"PR\" (pull request) builds that build the code as if the pull request were mer

Answer 1

According to https://github.com/actions/checkout/issues/15#issuecomment-524093065 and https://github.com/actions/checkout/issues/15#issuecomment-524107344, if you set your workflow to trigger on the pull_request event rather than the push event, the GITHUB_SHA will be the merge commit, so the checkout action will check out the result of the merge, which you can then build and run unit tests on.

Disclaimer: I haven't gotten into the beta yet, so I can't verify this information for myself; I can just pass on what others have said worked for them.

I've gotten into the beta now, so I can confirm that this works. I ran a build of the following workflow in my test repo:

name: Build PR

on: [pull_request]

jobs:
  build:

    strategy:
      matrix:
        os: [ubuntu-latest, windows-latest, macOS-latest]
        dotnet: [2.2.402, 3.0.100-rc1-014190]
    runs-on: ${{ matrix.os }}

    steps:
    # ... trimmed ...
    - name: Dump GitHub context
      env:
        GITHUB_CONTEXT: ${{ toJson(github) }}
      run: echo "$GITHUB_CONTEXT"
      if: runner.os != 'Windows'
    # ... trimmed ...

Here's a build log of that workflow running. The PR is here; the first commit on that PR is commit ID ec81c6f:

When I ran git fetch origin pull/10/merge:merge-pr-10 to fetch the merge commit, the commit I got was f1ea865, a merge of ec81c6f onto 44a09bc (which was the latest commit on my master branch at the time that PR was created). And notice the SHA that was actually built:

So just by using on: [pull_request] as the triggering event of my workflow, it did what I wanted. If you look at the PR's history, you'll see that I tried several things to see what triggered a new build: adding a comment, closing the repo, opening the repo... Here's what I found.

• Adding a comment did NOT trigger a new workflow run
• Pushing a new commit DID trigger a new workflow run
• Closing the PR did NOT trigger a new workflow run
• Reopening the PR DID trigger a new workflow run
• Adding a label to the PR did NOT trigger a new workflow run
• Removing a label from the PR did NOT trigger a new workflow run

Which is all as I would have expected.