Welcome to Compossible 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.
Getting started:
You currently need javac, nailgun, gpg and realpath or gcc installed.
CBT bootstraps from source. To install, just clone the repository.
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
import cbt._
class Build(context: cbt.Context) extends PackageBuild(context){
override def version = "0.6.1-SNAPSHOT"
override def groupId = "org.cvogt"
override def artifactId = "play-json-extensions"
override def dependencies = super.dependencies ++ Vector(
"com.typesafe.play" %% "play-json" % "2.4.4"
)
override def compile = {
println("Compiling...")
super.compile
}
def foo = "Hello World"
}
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 DefaultBuild 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/DefaultBuild.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.DefaultBuild.
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
Missing features in comparison with SBT
Not implemented yet, but rather easily possible without API changes or
major refactors is concurrently building / downloading dependencies and
running tests. Right now it is sequential.
SBT in comparison goes a step further and is conceptually able to also run tasks
within single project to run concurrently. If I wanted to do that in
CBT, it would require an API change. I would need to make tasks Monads,
which means wrapper types and comprehensions everywhere. That would
complicate ease of use and I am actually skeptical about the benefit.
How often to you need to run tasks in parallel within a single project?
"compile" happens before "package" before "publish".
CBT allows tasks to lazily depend on other tasks.
SBT currently does not, because it uses an Applicative, not a Monad, so
task dependencies are eager.
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.
