Like Alex Harsányi, I’ve been looking for a good, free-as-in-beer, alternative to Travis CI. For now, I’ve settled on GitHub Actions because using them is straightforward and because I saves me from creating yet another account with some other company.

GitHub Actions revolves around the concept of “workflows” and “actions”. Actions execute arbitrary Docker containers on top of a checked-out repository and workflows describe which actions need to be executed when a particular event occurs. During the execution of a workflow, all actions, including ones running in parallel, share the same physical workspace. All of this stuff is declaratively specified using HCL.

Here’s an example workflow:

workflow "demo" {
  on = "push"
  resolves = ["echo"]
}

action "make-a" {
  uses = "docker://alpine"
  runs = ["sh", "-c", "echo Hello > $GITHUB_WORKSPACE/a"]
}

action "make-b" {
  uses = "docker://alpine"
  runs = ["sh", "-c", "echo World > $GITHUB_WORKSPACE/b"]
}

action "echo" {
  needs = ["make-a", "make-b"]
  uses = "docker://alpine"
  runs = ["sh", "-c", "cat $GITHUB_WORKSPACE/a $GITHUB_WORKSPACE/b"]
}

This is saying that there is a workflow called “demo” that is executed whenever anything is pushed to the repository. That workflow’s goal is to execute the “echo” action, which happens to depend on actions “make-a” and “make-b”. When the workflow is triggered, those two actions are run first and the “echo” action only runs after they both succeed. In this particular example, each of the actions runs a shell command on top of the alpine docker image, but I could’ve picked any other image from Docker Hub or any existing GitHub Action repository. This page describes all of the various workflow configuration options.

If you save the above config in a file called .github/main.workflow in any GitHub repository and visit the “Actions” tab, then – assuming you have access to the GitHub Actions beta – you should see the pipeline execute almost immediately and output:

Hello
World

We can leverage all of this to test a Racket package is by using Jack Firth’s racket image (or you could roll your own and host it on Docker Hub yourself):

workflow "main" {
  on = "push"
  resolves = ["test"]
}

action "test" {
  uses = "docker://jackfirth/racket:7.2"
  runs = "/github/workspace/ci/test.sh"
}

Here are the contents of ci/test.sh:

#!/usr/bin/env bash

set -euo pipefail

pushd "$GITHUB_WORKSPACE"
raco pkg install --batch --auto testpackage/
raco test testpackage/

The script sets the working directory to $GITHUB_WORKSPACE, installs all of testpackage’s (a hypothetical package for the purposes of this article) dependencies and then runs its tests.

That’s all there is to it! With about 12 LOC we’ve put together a basic workflow that tests a package on every commit.

Gotchas & Limitations

Like I mentioned before, all actions in a workflow share the same workspace so it’s possible for actions to clash with one another when they operate on the filesystem. That’s something you have to keep in mind when designing your workflows.

Workflow and action names share a namespace. If you call your workflow “test” and your action “test”, you’ll get an error saying the workflow is invalid, but it won’t point out exactly why.

Finally, there’s no built-in support for notifications. When builds fail, you won’t notice unless you visit the Actions tab. For one of my non-OSS projects, I’ve set up a Telegram bot that I can use to notify a particular channel whenever builds succeed or fail. That works, but it’s fairly ugly because there doesn’t seem to be any way to conditionally execute actions (i.e. things like “if action a fails then run action b”), so I had to bundle the notification-handling code into each of my action scripts.