GitHub Actions: avoid double runs from on: [push, pull_request]

Artist’s depiction of your special snowflake build process.

I’ve often seen a GitHub Actions workflow defined with a trigger like:

on: [push, pull_request]

This means “run on any push or when a pull request is opened or updated”. While that may seem correct, it leads to double execution of the workflow when you push a commit and then create a pull request with it. You can see this in the status check details for the pull request:

GitHub checks showing two runs of “CI / test”, labelled “CI / test (pull_request)” and “CI / test (push)”.

Double execution means double the cost, extra waiting time, and increased chance of a spurious/flaky failure.

A better on clause looks like:

on:
  push:
    branches:
    - main
  pull_request:

This means “run for any push to the main branch or when a pull request is opened or updated”. If your workflow should run for tagged pushes as well, use:

on:
  push:
    branches:
    - main
    tags:
    - '**'
  pull_request:

This might be useful when your workflow contains a release job, as my open source projects do (example).

You’ll then see just a single run for your workflow in pull requests, like:

GitHub checks showing a single run of “CI / test”, labelled “CI / test (pull_request)”.

Fin

May your workflows run when you need, but no more,

—Adam

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