Merge pull request #810 from SethTisue/community-build-blog-post

blog post about the Scala community build

Author: SethTisue

_posts/2018-01-16-community-build-growth.md

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+---
+layout: blog-detail
+post-type: blog
+by: Seth Tisue
+title: "Scala community build grows to 141 projects, 2.8 million lines of code"
+---
+
+We on the Scala team would like to call some attention to a
+lesser-known but crucial component of the development effort behind
+Scala.  It's called the Scala community build.
+
+## What is it?
+
+It's a collection of open-source Scala code that includes many of the
+most-used libraries in the Scala ecosystem.
+
+But it's more than just a big pile of code; we actually compile all of
+these codebases, run their test suites, and rewire their builds to
+depend on each other, so only freshly built code, built by freshly
+built Scala, is involved.
+
+## Why do we do this?
+
+Having the community build as a backstop and testbed means we can
+confidently assess the impact of proposed changes to the Scala
+language, compiler, and standard library.
+
+Our Jenkins cluster runs the community build every day against the
+latest Scala nightly build.
+
+We often also run the community build against individual pull requests
+in the [scala/scala repo](https://github.com/scala/scala) to assess
+the impact of the PR and detect regressions before the PR is merged.
+
+## Has it helped?
+
+Definitely.  Over the past few years, the build has often caught
+regressions and unanticipated source-compatibility issues.
+
+During the Scala 2.12 cycle, feedback from the community build was key
+for guiding the work on SAMs and the new trait encoding.  And, seeing what
+went wrong in downstream projects as the 2.12 changes went in was a
+major source for developing the migration guidelines in the
+[2.12 release notes](https://github.com/scala/scala/releases/tag/v2.12.0).
+
+In the Scala 2.13 cycle, we expect the community build to play a
+similar role in transitioning first our own code, then the entire
+open-source ecosystem, to the
+[new collections library](http://www.scala-lang.org/blog/2017/02/28/collections-rework.html).
+We've also [begun using it](https://github.com/scala/community-builds/issues/609) to
+gauge our progress on Java 9 support.
+
+Library authors have also benefited.  The community build has
+often provided early warning of compatibility issues because
+of changes to Scala or changes to other libraries.  It has helped
+maintainers standardize their builds, keep their dependencies
+up-to-date, identify flaky tests, and shake out assorted other
+issues.
+
+## How big is it?
+
+The community build has been growing steadily since 2013.
+These days it includes:
+
+### 2.8 million lines of code
+
+That's a lot!
+
+The build uses a
+[custom compiler plugin](https://github.com/sethtisue/cloc-plugin) to
+make sure that only code that is actually compiled is counted.
+[cloc](https://github.com/AlDanial/cloc), the standard tool for counting
+lines of code, takes care of filtering out blank lines and comments.
+
+### 141 projects
+
+There are now 141 projects in the community build, as listed in the
+[config file](https://github.com/scala/community-builds/blob/2.12.x/configs/project-refs.conf).
+They are: acyclic, akka, akka-contrib-extra, akka-http,
+akka-http-cors, akka-http-session, akka-persistence-cassandra,
+algebra, ammonite, argonaut, atto, autowire, base64, better-files,
+blaze, breeze, cachecontrol, case-app, catalysts, cats, cats-effect,
+circe, circe-config, conductr-lib, coursier, discipline, dispatch,
+doodle, elastic4s, fansi, fastparse, fs2, genjavadoc, geny, gigahorse,
+github4s, http4s, http4s-websocket, jackson-module-scala, jawn-fs2,
+jawn, json4s, kind-projector, kxbmap-configs, lagom, lift-json,
+lightbend-emoji, log4s, machinist, macro-compat, macro-paradise,
+meta-paradise, metaconfig, mima, minitest, monix, monocle, multibot,
+nscala-time, nyaya, paiges, paradox, parboiled, parboiled2, pcplod,
+play, play-doc, play-json, play-webgoat, play-ws, pprint, pureconfig,
+sbinary, sbt-io, sbt-librarymanagement, sbt-testng, sbt, sbt-util,
+scala-async, scala-collections-laws, scala-continuations,
+scala-debugger, scala-gopher, scala-java8-compat, scala-js,
+scala-json-ast, scala-logging, scala-parser-combinators,
+scala-partest-interface, scala-partest, scala-records,
+pscala-refactoring, scala-ssh, scala-stm, scala-swing, scala-xml-quote,
+scalacheck, scalacheck-shapeless, scalafix, scalafmt, scalaj-http,
+scalachess, scaladex, scalalib, scalameta, scalameter, scalamock,
+scalapb-lenses, scalapb, scalaprops, scalariform, scalastyle,
+scalatags, scalatest, scalatex, scalaz, scalikejdbc, scallop,
+scodec-bits, scodec, scopt, scoverage, semanticdb-sbt, shapeless,
+simulacrum, sjson-new, sksamuel-exts, slick, sourcecode, specs2,
+spire, spray-json, ssl-config, tut, twirl, twitter-util, twotails,
+unfiltered, upickle, utest, zinc.
+
+Want to add your project to the community build?  See our
+[eligibility guidelines](https://github.com/scala/community-builds/wiki/Eligibility).
+
+## Learning more, getting involved
+
+The community build is documented in a
+[wiki](https://github.com/scala/community-builds/wiki).  Many of the
+questions you might have are already answered there.
+
+If you have a question or want to get involved in the community
+build or in open source work on Scala more generally, come to the Scala
+contributors [forum](https://contributors.scala-lang.org) or
+[chat room](https://gitter.im/scala/contributors).
+
+Especially involved or specialized discussions about the community
+build can move to the community build's own
+[Gitter room](https://gitter.im/scala/community-builds) and
+[GitHub issues](https://github.com/scala/community-builds/issues).
+
+## Credits
+
+The main
+[contributors](https://github.com/scala/community-builds/graphs/contributors)
+have been myself (Seth Tisue), Adriaan Moors, Grzegorz Kossakowski,
+Jason Zaugg, and Toni Cunei, all of whom are current or former
+employees of Lightbend.  Toni is also the primary author of
+[dbuild](https://github.com/lightbend/dbuild), the meta-build tool
+that makes the community build possible.
+
+The community build also couldn't exist without continual help and
+advice from the maintainers of the included projects.  You are
+marvelous!
+
+## Related projects
+
+You might also like to investigate the nascent
+[Dotty community build](https://github.com/lampepfl/dotty-community-build)
+and [sbt community build](https://github.com/sbt/sbt-standalone-build).