sbt

How to create a Scala 3 (Dotty) project with SBT

I can never remember how to create a Scala 3 (Dotty) project with SBT (in early 2019), so:

# create a new Dotty project
sbt new lampepfl/dotty.g8

# create a dotty project that cross compiles with scala 2
sbt new lampepfl/dotty-cross.g8

# start a dotty reply from within your sbt project
$ sbt

> console
scala> _

Here’s what an example interaction looks like — include SBT renaming my directory name to all lowercase, which brings me no joy:

Bloop’s compiler performance is ~29% faster than SBT (on at least one project)

I had read that Bloop was faster than Scala compiler tools like scalac and fsc, so I wondered if it was faster than SBT, and if so, how much faster. So I downloaded Eric Torreborre’s specs2 source code, which has 880 source code files, and compiled the entire project with both SBT and Bloop.

SBT performance

To test SBT’s speed, I ran all the commands from inside the SBT command prompt, which I usually do anyway to avoid the SBT/JVM startup lag time. I also ran clean and compile several times before recording SBT’s speed, because I thought that would be a better reflection of real-world usage and performance. I ran the tests four times, and the average time with SBT was 49 seconds, and that was very consistent, always coming in between 48 and 50 seconds.

Bloop performance

Using Jenkins with Scala, ScalaTest, SBT, and Git

I’ve used Jenkins before, but hadn’t used it in a while, so when I got it running with Scala, SBT, ScalaTest, and Git, I made some notes about how to configure it. You can get Jenkins going with Docker, but I just got Jenkins running by starting its WAR file like this:

java -jar jenkins.war

Jenkins with Scala, SBT, ScalaTest, and Git

My notes on getting everything up and running are a little cryptic, but if you have a little experience with Jenkins I hope they’ll make sense. Here they are:

Jenkins tutorials (Jenkins, Docker, Scala, SBT, Java, Maven, and Git)

As a brief note to self, these were the two best Jenkins tutorials I found in early 2019:

The first one shows how to run Jenkins with Docker, and the second one shows how to build a Java/Maven/Git project.

This tutorial on how to use Jenkins with Scala and SBT was also helpful:

ScalaCheck custom generator examples

Table of Contents1 - Custom generators2 - Built-in ScalaCheck generators3 - How to use ScalaCheck generators4 - More ScalaCheck generators

Writing custom generators for ScalaCheck can be one of the more difficult and/or time-consuming parts of using it. As a result I thought I’d start putting together a list of generators that I have written or seen elsewhere. Unfortunately I can’t credit all the ones I’ve seen in other places because I google’d and copied them many moons ago, but I’ll give credit/attribution to all the ones I can.

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Custom generators

This is a combination of generators I wrote, and some that I copied from other places and may have modified a little:

Scala SBT scalacOptions syntax/examples

As a quick note to self, here’s an example of how to set scalacOptions in an SBT build.sbt file:

scalacOptions ++= Seq(
    "-Xfatal-warnings",
    "-deprecation",
    "-feature",
    "-unchecked",
    "-language:implicitConversions",
    "-language:higherKinds",
    "-language:existentials",
    "-language:postfixOps"
)

As shown, scalacOptions lets you set Scala compiler options in your SBT project build.