This is the official repository for the Scala Programming Language standard library, compiler, and language spec.
To contribute in this repo, please open a pull request from your fork of this repository.
We do have to ask you to sign the Scala CLA before we can merge any of your work, to protect its open source nature.
For more information on building and developing the core of Scala, make sure to read the rest of this README!
In order to get in touch with other Scala contributors, join scala/contributors (Gitter) or post on contributors.scala-lang.org (Discourse).
Please report bugs at the scala/bug issue tracker. We use the scala/scala-dev tracker for coordinating bigger work items.
If you need some help with your PR at any time, please feel free to @-mention anyone from the list below, and we will do our best to help you out:
username talk to me about...@adriaanm
type checker, pattern matcher, infrastructure, language spec @SethTisue
getting started, build, developer docs, community build, Jenkins, library @retronym
compiler performance, weird compiler bugs, Java 8 lambdas, REPL @szeiger
collections, build @lrytz
back end, optimizer, named & default arguments @Ichoran
collections library, performance @viktorklang
concurrency, futures @axel22
concurrency, parallel collections, specialization @dragos
specialization, back end @janekdb
documentation @sjrd
interactions with Scala.js
P.S.: If you have some spare time to help out around here, we would be delighted to add your name to this list!
scala/
+--build.sbt The main sbt build script
+--lib/ Pre-compiled libraries for the build
+--src/ All sources
+---/library Scala Standard Library
+---/reflect Scala Reflection
+---/compiler Scala Compiler
+---/intellij IntelliJ project templates
+--spec/ The Scala language specification
+--scripts/ Scripts for the CI jobs (including building releases)
+--test/ The Scala test suite
+---/files Partest tests
+---/junit JUnit tests
+---/scalacheck ScalaCheck tests
+--build/ [Generated] Build output directory
You need the following tools:
MacOS and Linux work. Windows may work if you use Cygwin. Community help with keeping the build working on Windows is appreciated.
We are grateful for the following OSS licenses:
During ordinary development, a new Scala build is built by the previously released version. For short we call the previous release "starr": the stable reference release. Building with starr is sufficient for most kinds of changes.
However, a full build of Scala (a bootstrap, as performed by our CI) requires two layers. This guarantees that every Scala version can build itself. If you change the code generation part of the Scala compiler, your changes will only show up in the bytecode of the library and compiler after a bootstrap. See below for how to do a bootstrap build locally.
For history on how the current scheme was arrived at, see https://groups.google.com/d/topic/scala-internals/gp5JsM1E0Fo/discussion.
Once you've started an sbt
session you can run one of the core commands:
compile
compiles all sub-projects (library, reflect, compiler, scaladoc, etc)scala
/ scalac
run the REPL / compiler directly from sbt (accept options / arguments)dist/mkBin
generates runner scripts (scala
, scalac
, etc) in build/quick/bin
dist/mkPack
creates a build in the Scala distribution format in build/pack
test
runs the JUnit test, testOnly *immutable.ListTest
runs a subsetpartest
runs partest tests (accepts options, try partest --help
)publishLocal
publishes a distribution locally (can be used as scalaVersion
in other sbt projects)
set baseVersionSuffix := "-bin-abcd123-SNAPSHOT"
where abcd123
is the git hash of the revision being published. You can also use something custom like "-bin-mypatch"
. This changes the version number from 2.12.2-SNAPSHOT
to something more stable (2.12.2-bin-abcd123-SNAPSHOT
).-bin
string marks the version binary compatible. Using it in sbt will cause the scalaBinaryVersion
to be 2.12
. If the version is not binary compatible, we recommend using -pre
, e.g., 2.13.0-pre-abcd123-SNAPSHOT
.set ThisBuild / Compile / packageDoc / publishArtifact := false
to skip generating / publishing API docs (speeds up the process).If a command results in an error message like a module is not authorized to depend on itself
, it may be that a global SBT plugin (such as Ensime) is resulting in a cyclical dependency. Try disabling global SBT plugins (perhaps by temporarily commenting them out in ~/.sbt/0.13/plugins/plugins.sbt
).
We recommend to keep local test files in the sandbox
directory which is listed in the .gitignore
of the Scala repo.
Note that sbt's incremental compilation is often too coarse for the Scala compiler codebase and re-compiles too many files, resulting in long build times (check sbt#1104 for progress on that front). In the meantime you can:
To perform a bootstrap using sbt
starr
) is used to build / publish the actual build.Assume the current starr
version is 2.12.0
(defined in versions.properties) and the current version is 2.12.0-SNAPSHOT
(defined in build.sbt). To perform a local bootstrap:
publishLocal
(you may want to specify a custom version suffix and skip generating API docs, see above).sbt -Dstarr.version=<version>
where <version>
is the version number you published locally.starr
, set every scalaBinaryVersion := "2.12.0-M4"
. This is not required if the version you published locally is binary compatible, i.e., if the current starr
is a 2.12.x release and not a milestone / RC.The last step is required to resolve modules (scala-xml, scala-partest, etc). It assumes that the module releases for the current starr
work (in terms of binary compatibility) with the local starr that you published locally. A full bootstrap requires re-building the all the modules. On our CI this is handled by the bootstrap script, but it (currently) cannot be easily executed locally.
You may use IntelliJ IDEA (see src/intellij/README.md), the Scala IDE for Eclipse (see src/eclipse/README.md), or ENSIME (see this page on the ENSIME site).
In order to use IntelliJ's incremental compiler:
dist/mkBin
in sbt to get a build and the runner scripts in build/quick/bin
Now you can edit and build in IntelliJ and use the scripts (compiler, REPL) to directly test your changes. You can also run the scala
, scalac
and partest
commands in sbt. Enable "Ant mode" (explained above) to prevent sbt's incremental compiler from re-compiling (too many) files before each partest
invocation.
Our guidelines for contributing are explained in CONTRIBUTING.md. It contains useful information on our coding standards, testing, documentation, how we use git and GitHub and how to get your code reviewed.
You may also want to check out the following resources:
Once you submit a PR your commits will be automatically tested by the Scala CI.
If you see a spurious build failure, you can post /rebuild
as a PR comment. The scabot README lists all available commands.
If you'd like to test your patch before having everything polished for review, feel free to submit a PR and add the WIP
label. In case your WIP branch contains a large number of commits (that you didn't clean up / squash yet for review), consider adding [ci: last-only]
to the PR title. That way only the last commit will be tested, saving some energy and CI-resources. Note that inactive WIP PRs will be closed eventually, which does not mean the change is being rejected.
CI performs a full bootstrap. The first task, validate-publish-core
, publishes a build of your commit to the temporary repository https://scala-ci.typesafe.com/artifactory/scala-pr-validation-snapshots. Note that this build is not yet bootstrapped, its bytecode is built using the current starr
. The version number is 2.12.2-bin-abcd123-SNAPSHOT
where abcd123
is the commit hash. For binary incompatible builds, the version number is 2.13.0-pre-abcd123-SNAPSHOT
.
You can use Scala builds in the validation repository locally by adding a resolver and specifying the corresponding scalaVersion
:
$ sbt
> set resolvers += "pr" at "https://scala-ci.typesafe.com/artifactory/scala-pr-validation-snapshots/"
> set scalaVersion := "2.12.2-bin-abcd123-SNAPSHOT"
> console
Note that the scala modules are currently not built/published against the tested version during CI validation.
The Scala CI builds nightly download releases (including all modules) and publishes them to the following locations:
The CI also publishes nightly API docs:
Using a nightly build in sbt is explained in this Stack Overflow answer
The Scala CI runs as a Jenkins instance on scala-ci.typesafe.com, configured by a chef cookbook at scala/scala-jenkins-infra.
The build bot that watches PRs, triggers testing builds and applies the "reviewed" label after an LGTM comment is in the scala/scabot repo.
The Scala community build is an important method for testing Scala releases. A community build can be launched for any Scala commit, even before the commit's PR has been merged. That commit is then used to build a large number of open-source projects from source and run their test suites.
To request a community build run on your PR, just ask in a comment on the PR and a Scala team member (probably @SethTisue) will take care of it. (details)
Community builds run on the Scala Jenkins instance. The jobs are named ..-integrate-community-build
. See the scala/community-builds repo.
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