pkl-gha

A Pkl template for writing GitHub Action workflows.

What?

Pkl is a configuration as code language with rich validation. YAML, the language used for GitHub Actions on the other hand, is a configuration language with no validation at all. We have to rely on third-party tools or IDE support to validate our GitHub Actions. While this will get better over time, it's still not as good as having a language with rich validation out of the box.

This is where this template comes in. It allows you to write your GitHub Action Workflows in Pkl and then compile them (using the Pkl cli) to YAML. The generated YAML output, if successfully converted, is definitely YAML validated and ready to be used as your Action Workflows.

How?

1. Write a Pkl file and amend this template

amends "package://pkg.pkl-lang.org/github.com/stefma/pkl-gha/com.github.action@[LATEST_VERSION]#/GitHubAction.pkl"

name = "Test"

on {
  // Define your `on` triggers. E.g.:
  push {
    branches {
      "main"
    }
  }
  pull_request {}
}

jobs {
  // Define your `jobs`. E.g.: 
  ["test"] {
    `runs-on` = new UbuntuLatest {} // Could also be a string like "ubuntu-latest"
    // Define your `steps`. E.g.:
    steps {
      new {
        name = "Checkout"
        uses = "actions/checkout@v4"
        with {
          ["fetch-depth"] = 0
        }
      }
      new {
        name = "Setup nexus credentials"
        run = """
          mkdir ~/.gradle
          echo "systemProp.nexusUsername=${{ secrets.NEXUS_USERNAME }}" >> ~/.gradle/gradle.properties
          echo "systemProp.nexusPassword=${{ secrets.NEXUS_PASSWORD }}" >> ~/.gradle/gradle.properties
        """
      }
      new {
        name = "Test android app"
        run = "./gradlew testDebugUnitTest"
      }
    }
  }
}

2. Install the Pkl cli

brew install pkl

3. Convert the Pkl file to Yaml

pkl eval path/to/your/pkl/file.pkl -o path/to/your/pkl/file.yaml

Or alternatively for all files in the .github/workflows directory:

pkl eval path/to/your/pkl/files/*.pkl -o path/to/your/pkl/files/%{moduleName}.yml

Why?

• Strong typing: Pkl is a strongly typed language. This means that you can't accidentally use a wrong type in your configuration.
• Simplicity: Strong validation and strong typing but still simple to write.

Examples

You can find real-life examples in the .github/pkl-workflows directory of this repository. There are also some examples in the examples directory.

The (right now) supported templates looks like that:

name: String
on: On
env: EnvironmentVariables?
concurrency: Concurrency?
permissions: (*Permissions|"read-all"|"write-all")?
jobs: Mapping<String, Job>

The template itself as well as the class definitions can be found in the GitHubAction.pkl file.

Releasing

Step 1: Make sure you're on the main branch and pull the latest changes.

git checkout main
git pull origin main

Step 2: Create a git tag in form of com.github.action@[SEMVER_VERSION].

git tag com.github.action@[SEMVER_VERSION]

Step 3: Push the tag to the remote repository.

git push origin com.github.action@[SEMVER_VERSION]

Step 4: The tag creates a new release on GitHub. Go to the releases page and edit the new release. Put some information about the changes in the description and publish the release.

Step 5: Update SNAPSHOT version in PklProject to the next version and push the changes.

git add PklProject
git commit -m "Bump snapshot version"
git push origin main