I recently enabled continuous integration of Positron using TaskCluster’s support for GitHub repositories. I’ve used Travis CI to integrate other GitHub projects, but Positron is too large for Travis to build without timing out, since it builds all of Gecko. So I needed an alternative.

Caveat: TaskCluster only supports GitHub repositories in the mozilla organization or another org that is explicitly configured for it, as described by Setting up Taskcluster with a Github Organization. So it won’t work with your personal fork.

Also, while the Positron repository is based on gecko-dev, I didn’t use GitHub’s “fork” feature to create it, since GitHub won’t let you fork a repo to another repo in the same organization. Instead, I created a new repository and then copied gecko-dev’s commits to it, as described in Copy/fork a git repo on github into same organization.

(I also had to push the copied commits to GitHub in batches, as described in Github remote push pack size exceeded. And I had to push the first batch via special syntax, per Pushing a large github repo fails with “unable to push to unqualified destination: master”.)

To enable CI, I first created this Docker image, based on Ubuntu 14.04 (Trusty), that includes the Mozilla build toolchain and dependencies installed by Gecko’s bootstrap.py script. The image also includes the taskcluster-vcs utility, which caches gecko-dev and clones from the cache so that TaskCluster pulls from GitHub are lighter-weight.

Here’s the Dockerfile for that image:

FROM ubuntu:trusty

RUN apt-get update -y && \
    apt-get install -y \
      curl \
      git \
      nodejs \
      nodejs-legacy \
      npm \
      python \
      wget

RUN npm install -g taskcluster-vcs

RUN wget -O bootstrap.py https://raw.githubusercontent.com/mozilla/positron/master/python/mozboot/bin/bootstrap.py && \
    python bootstrap.py --no-interactive --application-choice=browser

Then I replaced the upstream .taskcluster.yml file with one that clones and builds Positron when a developer submits a pull request or lands a change. .taskcluster.yml is like .travis.yml, but for TaskCluster. Here’s that file:

version: 0
metadata:
    name: "Positron"
    description: "continuous integration for Positron"
    owner: "{{ event.head.user.email }}"
    source: "{{ event.head.repo.url }}"
tasks:
    - provisionerId: "{{ taskcluster.docker.provisionerId }}"
      workerType: "{{ taskcluster.docker.workerType }}"
      extra:
          github:
              env: true
              events:
                  - pull_request.opened
                  - pull_request.synchronize
                  - pull_request.reopened
                  - push
      payload:
          maxRunTime: 7200 # seconds (i.e. two hours)
          image: "mykmelez/docker-build-positron:latest"
          command:
              - "/bin/bash"
              - "--login"
              - "-c"
              - "tc-vcs checkout repo https://github.com/mozilla/gecko-dev $GITHUB_HEAD_REPO_URL $GITHUB_HEAD_BRANCH &&
                 cd repo/ && SHELL=/bin/bash ./mach build"
      metadata:
          name: "checkoutandbuild"
          description: "check out and build the repository"
          owner: "{{ event.head.user.email }}"
          source: "{{ event.head.repo.url }}"

Finally, I added TaskClusterRobot to the list of collaborators in the repo’s Settings > Collaborators & teams list, giving it Write permissions, so it can annotate pull requests with icons representing the state of the job, just like Travis does:

Et voilà, continuous integration for Positron!

(Once Positron starts running Node and Electron tests, I’ll add tasks to run those tests and report their results.)