Cannot use parent specifiers in the ref

[mathstuf]

I'd like to run an action on a pull_request and check out the actual content of the PR, not a merge with master (because I want it to run even if there is a merge conflict among other reasons). Support for specifying this has been requested on the community forum.

I've tried the following:

with:
  ref: ${{ github.ref }}^2

Which causes a failure because it tries to do:

 git fetch --tags --prune --progress --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/pull/3/merge^2:refs/remotes/pull/3/merge^2

which is an invalid refspec.

Doing this seems to just get completely ignored:

with:
  ref: ${{ github.sha }}^2

I haven't found a way to use $GITHUB_SHA yet either (it seems to be used literally when in a with block).

[ericsciple]

@mathstuf consider adding a run step after checkout, and git reset --hard HEAD^2

[mathstuf]

But is that going to mean that GITHUB_SHA is wrong?

[ericsciple]

Yes. GITHUB_SHA is not set by the checkout action. It is from the server event payload.

[mathstuf]

And while that may be a workaround, not being able to specify a valid Git refname in such a way (and that gets silently ignored) seems like a bug in any case.

[mathstuf]

Also of note is that manual checkout misses all of the submodule sync/update, depth options, etc. available through the action.

[ericsciple]

from the pr event payload, i think ${{ github.event.after }} is the SHA you want

[peter-evans]

I think this will checkout the merging branch instead of the merge commit.

      - uses: actions/checkout@master
        with:
          ref: ${{ github.head_ref }}

Edit: I misunderstood. I think this only works for non-fork PRs.

[ericsciple]

@peter-evans instead of refs/pull/merge/<number> iirc refs/pull/<number> contains the commit (for forks and non forks). i may be wrong?

[peter-evans]

@ericsciple I tested the following but it didn't work and gave the error ##[error]fatal: couldn't find remote ref refs/pull/281

on: pull_request
jobs:
  pullRequest:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v1
        with:
          ref: refs/pull/${{ github.event.number }}

What does seem to work for me is the following. But to make this work for forks as well you need to use a repo scoped PAT. Additionally, specifying the path is necessary to keep fork and non-fork checkouts at the same path for the rest of your workflow.

      - uses: actions/checkout@v1
        with:
          token: ${{ secrets.REPO_ACCESS_TOKEN }}
          repository: ${{ github.event.pull_request.head.repo.full_name }}
          ref: ${{ github.event.pull_request.head.ref }}
          path: ${{ github.event.repository.name }}

[ericsciple]

i'll play with this a bit, i think there's a different way

[ericsciple]

@peter-evans sorry its refs/remotes/pull/###/head or pull/###/head

i played around with this locally by fetching everything under pull:

git fetch origin '+refs/pull/*:refs/remotes/pull/*'
git branch --list --remote
git log refs/remotes/pull/70/head

[ericsciple]

@mathstuf it sounds like the following solution will work:

on: pull_request
jobs:
  pullRequest:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v1
        with:
          ref: refs/pull/${{ github.event.number }}/head

[mathstuf]

Thanks, I'll try that out when I get a chance. However, I feel like that shouldn't be necessary and that ^2 should still work (really, anything git rev-parse accepts that resolves to a commit).

[ericsciple]

I'll update the README with the scenario: checkout the head commit of a PR, rather than the merge commit.

Leaving this issue open and i'll mark it as enhancement.

Also interested in other scenarios.

[mrrobot47]

@ericsciple first of all, thanks a lot for your replies on this thread. It helped me a lot to configure my action.

In the README update you have used github.event.after which works for PR synchronize but fails when PR is created and does a checkout of the merge commit.

To handle the checkout of head commit during PR creation as well as synchronize either:

1. refs/pull/${{ github.event.number }}/head (as you rightly suggested in prev. comment)
   or
2. github.event.pull_request.head.sha

can be used. I have created a PR with the second option to update the README as that felt better to read and explained exactly as the title read.

[ericsciple]

@mrrobot47 thanks. also note, the first option is a race condition because the PR can be updated before the job starts (ref update)

[mathstuf]

FWIW, the way GitLab-CI seems to get around that is that CI jobs pull a refs/pipelines/${{ pipeline_id }} ref instead.