Saturday, 5 January 2019

GitHub Actions and Yarn

I'd been meaning to automate the npm publishing of ts-loader for the longest time. I had attempted to use Travis to do this in the same way as fork-ts-checker-webpack-plugin. Alas using secure environment variables in Travis has unfortunate implications for ts-loader's test pack.

Be not afeard. I've heard there's a new shiny thing from GitHub that I could use instead... It's a sign; I must use it!

GitHub Actions are still in beta. Technically Actions are code run in Docker containers in response to events. This didn't mean a great deal to me until I started thinking about what I wanted to do with ts-loader's publishing flow.

Automate What?

Each time I publish a release of ts-loader I execute the following node commands by hand:

  1. yarn install - to install ts-loader's dependencies
  2. yarn build - to build ts-loader
  3. yarn test - to run ts-loader's test packs
  4. npm publish - to publish the release of ts-loader to npm

Having read up on GitHub Actions it seemed like they were born to handle this sort of task.

GitHub Action for npm

I quickly discovered that someone out there loves me had already written a GitHub Action for npm.

The example in the README.md could be easily tweaked to meet my needs with one caveat: I had to use npm in place of yarn. I didn't want to switch from yarn. What to do?

Well, remember when I said actions are code run in Docker containers? Another way to phrase that is to say: GitHub Actions are Docker images. Let's look under the covers of the npm GitHub Action. As we peer inside the Dockerfile what do we find?

FROM node:10-slim

Hmmmm.... Interesting. The base image of the npm GitHub Action is node:10-slim. Looking it up, it seems the -slim Docker images come with yarn included. Which means we should be able to use yarn inside the npm GitHub Action. Nice!

GitHub Action for npm for yarn

Using yarn from the GitHub Action for npm is delightfully simple. Here's what running npm install looks like:

# install with npm
action "install" {
  uses = "actions/[email protected]"
  args = "install"
}

Pivoting to use yarn install instead of npm install is as simple as:

# install with yarn
action "install" {
  uses = "actions/[email protected]"
  runs = "yarn"
  args = "install"
}

You can see we've introduced the runs = "yarn" and after that the args are whatever you need them to be.

Going With The Workflow

A GitHub Workflow that implements the steps I need would look like this:

workflow "build, test and publish on release" {
  on = "push"
  resolves = "publish"
}

# install with yarn
action "install" {
  uses = "actions/[email protected]"
  runs = "yarn"
  args = "install"
}

# build with yarn
action "build" {
  needs = "install"
  uses = "actions/[email protected]"
  runs = "yarn"
  args = "build"
}

# test with yarn
action "test" {
  needs = "build"
  uses = "actions/[email protected]"
  runs = "yarn"
  args = "test"
}

# filter for a new tag
action "check for new tag" {
  needs = "Test"
  uses = "actions/bin/[email protected]"
  args = "tag"
}

# publish with npm
action "publish" {
  needs = "check for new tag"
  uses = "actions/[email protected]"
  args = "publish"
  secrets = ["NPM_AUTH_TOKEN"]
}

As you can see, this is a direct automation of steps 1-4 I listed earlier. Since all these actions are executed in the same container, we can skip from yarn to npm with gay abandon.

What's absolutely amazing is, when I got access to GitHub Actions my hand crafted workflow looked like it should work first time! I know, right? Don't you love it when that happens? Alas there's presently a problem with filters in GitHub Actions. But that's by the by, if you're just looking to use a GitHub Action with yarn instead of npm then you are home free.

You Don't Actually Need the npm GitHub Action

You heard me right. Docker containers be Docker containers. You don't actually need to use this:

  uses = "actions/[email protected]"

You can use any Docker container which has node / npm installed! So if you'd like to use say node 11 instead you could just do this:

  uses = "docker://node:11"

Which would use the node 11 image on docker hub.

Which is pretty cool. You know what's even more incredible? Inside a workflow you can switch uses mid-workflow and keep the output. That's right; you can have a work flow with say three actions running uses = "docker://node:11" and then a fourth running uses = "actions/[email protected]". That's so flexible and powerful!

Thanks to Matt Colyer and Landon Schropp for schooling me on the intricicies of GitHub Actions. Much ❤