This project is an effort to build Stackage with arbitrary GHC development versions and, in particular, with the development HEAD. This allows us to detect regressions during GHC development much faster.

The process is currently run on Circle CI 4 times a day and can be described as the following progression of steps:

1. Start with the docker container that is used to build Stackage Nightly, snoyberg/stackage:nightly.

2. To avoid re-compiling GHC every time we use build artifacts and some associated metadata provided by ghc-artifact-collector.

3. Download Stackage curator that is used to execute build plans.

4. Reuse a plan from the stackage-nightly repository. These plans are known to build fine, so they are OK for us in most cases, and even if a couple of packages cannot be built it's not a big deal and can be detected as usual (see below).

5. Update, if necessary, the downloaded plan setting source URLs in case we need to use not-yet-released versions of some packages.

6. Execute the chosen build plan and save the build log.

7. Parse the build log and turn it into a build report, store it for future runs.

8. Compare two most recent build reports and detect regressions. Fail if there are suspicious changes (which are necessarily due to some changes in GHC, because we build always with the same build plan, only changing GHC commits).

9. GHC team is notified if the build fails.

The Stackage snapshot used for the builds is updated manually. The reason is that we don't want extra noise and volatility associated with changing snapshots.

Updating the snapshot is usually as simple as editing .circleci/config.yml and changing the line

  BUILD_PLAN: nightly-2018-10-23

to something else.

Occasinally, our docker image also needs to be rebuilt on top of the latest snoyberg/stackage:nightly image—for instance, if a newly added package needs an extra system dependency. The corresponding Dockerfile is at .circleci/images/primary/Dockerfile. The image then needs to be uploaded to Docker Hub and the following line updated in .circleci/config.yml:

  docker:
    - image: rctwg/stackage-head:0.3.2

You can see when snoyberg/stackage:nightly was last updated here.

• The original blog post introducing the initiative
• A talk from HIW'17

Copyright © 2018 Tweag I/O

Distributed under BSD 3 clause license.