How to detect a pull request from a fork

[jamime]

I have a project that uses cypress dashboard. To access this we use 20 runners (our max concurrency) and a secret token.

This uses

fail-fast: false

otherwise when one runner fails they will terminate without updating the cypress dashboard.
cypress-io/github-action#48

When we recieve a PR from a fork it takes up all 20 of our available runners, but only uses 1 (because it does not have the secret token). This takes ~3 hours.

Is it possible to detect if the PR came from a fork so I can adjust the matrix size?

[jamime]

I found the following works (ensure you replace org/repo).

Fork:

if: ${{ github.event.pull_request.head.repo.full_name != 'org/repo' }}

Not a fork:

if: ${{ github.event.pull_request.head.repo.full_name == 'org/repo' }}

[tunetheweb]

This also seems to work which is more generic, than actually naming the repo:

if: github.event.pull_request.head.repo.full_name == github.repository

[felipecrs]

In case it’s useful for someone, I wanted to filter pull_requests which does not have write permissions, which are:

• PRs coming from forks
• PRs coming from dependabot

I was able to do so by using:

if: github.event.pull_request.head.repo.full_name == github.repository && github.actor != 'dependabot[bot]'

[eiffel-fl]

Already found the dependabot part, but I was looking for the fork part! Thank you for it!

[islami00]

Hi, you can now check if fork directly using the boolean provided in the payload:
Not fork:
if: "! github.event.pull_request.head.repo.fork "
Fork:
if: " github.event.pull_request.head.repo.fork "

[gluxon]

I heads up to others trying this: github.event.pull_request.head.repo.fork describes the repo making the PR, not the PR itself. This value will be true for any PRs from a forked repo, even if the PR is targeting the fork itself.

If you're looking for whether a pull request has a head branch from a different repo, an earlier answer is probably better.

• https://github.com/orgs/community/discussions/25217#discussioncomment-3246902