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Welcome to Chris' Build Tool (CBT) for Scala

Fun, fast, intuitive, composable and statically checked builds written in Scala.

Currently CBT has been tested in OSX only. Adding support for Unix and Windows should not be hard. Please contribute back if you mange :).

CBT supports the basic needs for Scala builds right now. Composing, compiling, running, testing, packaging, publishing. Tasks outside of these, such as building manuals will require easy custom code. If you integrate something, consider doing it as traits that you make available as a library that other builds can depend on and mix in.

Slides and video from CBT talk from NEScala 2016: https://github.com/cvogt/talks/raw/master/2016-03-04_NEScala-2016_A-Vision-For-Scala-Builds.pdf https://www.youtube.com/watch?v=5HfKw3hgdOM

Getting started

Dependencies

You currently need javac, nailgun, gpg and realpath or gcc installed.

Installing

CBT bootstraps from source. To install, just clone the repository.

Using

To use, just call the cbt bash script. You will see CBT first building up itself, then trying to start your build.

The easiest CBT build requires no script. It compiles source files from the current directory and from src/ into the target folder. Try calling cbt compile. If you have a class called Main with a main method, try cbt run. Put a source file with a Main class into test/ in order for cbt test to run it. It will see your main code.

If you need more than this, like dependencies, create a scala file in build/ that describes your build. Here is an example

// build/build.scala
class Build(val context: cbt.Context) extends PackageJars {
  override def defaultVersion = "0.6.1"

  override def name = "play-json-extensions"

  override def groupId = "org.cvogt"

  override def dependencies =
    super.dependencies ++
      Resolver(mavenCentral).bind(
        // encouraged way to declare dependencies
        ScalaDependency("com.typesafe.play", "play-json", "2.4.4"),
        MavenDependency("joda-time", "joda-time", "2.9.2")
      )
  
  override def compile = {
    println("Compiling...")
    super.compile
  }

  def foo = "Hello World"
}

Dependencies could also be declared using SBT style.

class Build(val context: cbt.Context) extends PackageJars {
...
// sbt compatible dependencies definition
override def dependencies =
  super.dependencies ++
    Resolver(mavenCentral).bind(
      "com.typesafe.play" %% "play-json" % "2.4.4",
      "joda-time" % "joda-time" % "2.9.2"
    )
...
}      

Now you can call methods of this class through cbt. Try cbt foo. You can see how your build is configured via overrides.

call cbt to see a full list of available commands for this build.

Look into the class PackageBuild (and it's super class BasicBuild) in CBT's source code to see their details. The source code is really simple. Don't shy away from looking, even as a beginner. No crazy stuff, I promise ;). You can find the relevant code in CBT's stage2/BasicBuild.scala

I order to keep executing the same command triggered by file changes use cbt loop <command>.

You can find example builds in CBT's own test/ folder. Not all of them have a build file, in which case CBT uses the default cbt.BasicBuild.

A folder build/ can have its own folder build/ inside in order to add source or maven dependencies to your build. Eventually you'll be able to also choose the CBT and Scala versions for target builds. Make sure you extend cbt.BuilBuild instead of cbt.Build, in order to automatically trigger building of the target build.

cbt is fast. It uses Nailgun to keep the JVM hot. It uses the Java WatchService (respectively a fast OSX port of it) for instant triggering re-compilation on file changes. Use cbt loop compile.

CBT concepts

There two essential primitives available in build scripts for composing modular projects:

1. Dynamically compiling and loading Build scripts in other directories and calling methods (aka tasks) on them to compile, get the classpath, ask for version numbers, etc.

   This allows to do a lot of things just like that: Multi-project builds, source dependencies, builds of builds and allowing tests simply as dependent projects of the main project, etc.

2. Maven dependencies

   I wrote my own 50 LOC Maven resolver. It's super quick and I have yet see it not to being able to handle something. I know cases exist, but seem rare. alexarchambault's Coursier can be used as a more complete drop-in.

Build scripts also have access to a small unsurprising library for

• triggering dependencies to build / download and get the classpath
• compiling Java / Scala code using zinc with given class paths
• running code
• packaging jars
• signing / publishing to sonatype/maven

Scala.js support

CBT supports cross-project Scala.js build. It preserves same structure as in SBT (https://www.scala-js.org/doc/project/cross-build.html)

1. Example for user scalajs project is in: $CBT_HOME/cbt/examples/build-scalajs
2. $CBT_HOME/cbt compile Will compile JVM and JS sources $CBT_HOME/cbt jsCompile Will compile JS sources $CBT_HOME/cbt jvmCompile Will compile JVM sources
3. $CBT_HOME/cbt fastOptJS and $CBT_HOME/cbt fullOptJS Same as in Scala.js sbt project

Note: Scala.js support is under ongoing development.

Currently missing features:

• No support for jsDependencies: It means that all 3rd party dependencies should added manually, see scalajs build example
• No support for test

Missing features in comparison with SBT

Not implemented yet, but rather easily possible without API changes or major refactors is concurrently building dependencies and running tests. Right now it is sequential. Maven downloads already happen in parallel as well as some tasks like packaging.

Another edge case that may need a solution is dynamically overwriting tasks. SBT allows that. Classes and traits are static. The only use cases I know are debugging, cross builds and the sbt release plugin. A solution could be code generating traits at build-time and mixing them in ad-hoc. It's a build-tool after all. Build-time code-generation and class loading is not rocket science. But there may be simpler solutions for the cases at hand. And they are edge cases anyways.