Scala community build grows, adds Scala 2.13 and JDK 11

Friday 18 January 2019

Seth Tisue

In a January 2018 blog post we introduced the Scala community build, a collection of open-source Scala code that includes many of the most-used libraries in the Scala ecosystem.

The community build is used to test changes to the Scala compiler, enabling Scala the language and Scala the ecosystem of libraries to evolve in tandem with each other.

This post highlights the progress the community build has made in the last year.

Overall growth

We currently have 185 projects and a total of 3.2 million lines of code. (A year ago, we had 141 projects and 2.8 million lines.)

An especially notable project added recently was Apache Kafka, thanks to the efforts of Enno Runne at Lightbend.

Other projects added in the last year include: airframe, akka-http-json, akka-persistence-jdbc, argonaut-shapeless, better-monadic-for, boopickle, circe-derivation, classpath-shrinker, classutil, curryhoward, decline, eff, enumeratum, expecty, export-hook, fast-string-interpolator, giter8, grizzled, jsoniter-scala, kittens, linter, magnolia, mercator, metaconfig, metrics-scala, mouse, pascal, perfolation, portable-scala-reflect, refined, scala-collection-compat, scala-java-time, scala-newtype, scala-sculpt, scalajson, scalasti, scalaz8, scapegoat, scribe, scrooge-shapes, scrooge, silencer, singleton-ops, sttp, testz, wartremover.

See also the full list of all included projects.

JDK 11 added

With a JDK 11 community build now in place, we are protected from any more bugs like the bug that required Scala 2.12.5 to be withdrawn.

We added a JDK 9 edition of the community build in March 2018, starting with just a half-dozen projects. By June, 119 projects were passing. Since then we moved to JDK 10 and then to JDK 11. Today, 165 projects are passing – almost 90 percent.

(If it seems worrisome that several dozen projects still fail, consider the following. In order for a project to pass, it must both build and run on on JDK 11. It’s fairly rare for a Scala library to have any trouble running on JDK 11, using published artifacts built on JDK 8. In the community build context, most failures are minor build problems, not actual runtime problems.)

This GitHub ticket tracks progress on getting the remaining libraries passing.

Project maintainers can help by adding this to their .travis.yml files:

- oraclejdk8
- openjdk11

(These are the JDKs that the community build uses, and that open source contributors are likeliest to be using.)

Scala 2.13 added

There are currently 79 projects that build (and whose test suites pass) with the latest Scala 2.13 nightly build. This number has been gradually growing ever since 2.13’s new collections API landed in April.

Having this many projects passing gives us substantial confidence already that the new collections API in 2.13, and other changes, are fundamentally sound. Most projects have needed only small changes around the edges to cross-compile against 2.11, 2.12, and 2.13.

This GitHub ticket tracks progress on getting even more libraries passing in time for the 2.13.0 release in early 2019.

Learning more, getting involved

See last year’s blog post. The links it contains are still valid.

And what about about Scala 3? As the Dotty team tells us, “Dotty now has a set of widely-used community libraries that are built against every nightly Dotty snapshot. Currently this includes ScalaPB, algebra, scalatest, scopt and squants. Join our community build to make sure that our regression suite includes your library.”


I (Seth Tisue) am the primary maintainer of the Scala community build, as a member of the Scala team at Lightbend. Toni Cunei, from the tooling team at Lightbend, is the primary author of dbuild, the meta-build tool that makes the community build possible.

The community build couldn’t exist without continual help and advice from the maintainers of the included projects.