Scala Center monthly update: mid-Sept to mid-October

At a glance


  • #332, implement goto

definition with low CPU and memory overhead.


Worksheet mode for Dotty IDE

We have been working on supporting a [worksheet mode in Dotty

IDE]( Worksheets are interactive buffers in an editor

that can evaluate expressions and display their results. They offer a simple interface to quickly

try out things during the development process.

Worksheets have been merged in Dotty and will be part of the next release.

Configure new Scala projects from Dotty IDE

In order to improve the user experience for new Scala developers, Dotty IDE will now offer to create

a new sbt project when a Scala file is opened, and then configure itself automatically.

This way, getting started with Scala and getting help from an IDE becomes as simple as creating a

new Scala file in an empty directory.

This work has been merged in Dotty IDE and will be part of the next release.

Integrate Dotty IDE with sbt server

There are currently two ways to start Dotty IDE:

  1. Type launchIDE in an existing sbt shell

  2. Open VSCode in a directory that contains an up-to-date IDE configuration

This situation is not optimal, because we want Dotty IDE to stay current with the build definition

that sbt has. Dotty IDE will now communicate with sbt server to trigger the generation of the

configuration files that Dotty IDE needs.

In the future, we can imagine more integrations between

Dotty IDE and sbt (running tests, etc.).

This work has been merged in Dotty IDE and willbe part of the next release.

Other improvements to Dotty IDE

In some cases, Dotty IDE would be confused when using go to definition on overridden methods and

would not show all the possible alternatives.

A bug caused all trees that where unpickled from TASTY rather than read from source to be excluded

in all searches. This has been fixed.

Dotty IDE used to have difficulty selecting what symbol to jump to when doing go to definition

on constructor calls. It learned how to distinguish between them and be smart about its choices.

Dotty IDE mainly works within a single project. For instance, it is not able to rename symbols

between different projects, and will only find references within a single project. We are currently

working on adding support for multi-project setups and hope to have it integrated in the next

release of Dotty.


Mainly worked on the video lectures of the “Programming Reactive

Systems” MOOC. Coordinated the recording of Roland Kuhn’s videos,

Reviewed the videos after they were edited, also reviewed

Konrad Malawski’s videos, and prepared a couple of lectures to record.

Introduced changes to the grading infrastructure so that it

can used for internal courses at EPFL.

Deployed the new sbt-1-based graders.

Hired a couple of new teaching assistants.

Starting filling the course content on the edX portal.

Build pipelining

Build pipelining is a technique to start the compilation of modules in a build

before their dependencies have finished compilation. An experimental

implementation of build pipelining has been merged to master in


  1. Added more projects to our community build such as Finagle or Scalding.

  2. Benchmarked batch compilation of big builds. The current results can still

change, but on average We see an improvement between 0 and 30% in compilation

time on an 8-core machine (4 physical cores, 4 virtual cores). We can expect

more accentuated performance benefits in local development, where doing

incremental compilation or compiling a subset of the build graph which

tends to exhibit more sequential dependencies than the full build graph.

  1. Started writing a technical document explaining in depth the feature, its

trade-offs and design. There are many trade-offs in the context of mixed

Java and Scala compilation and a heavy use of macros.

This feature is being prepared for production-ready use. It will be supported

in 2.11.x, 2.12.x and 2.13.x only.



  • moved the sbt plugins to a separate repository, to lower CI build times on the main repository (#915)

  • remove scala 2.10 support

  • help publish downstream dependencies for scala 2.13.0-M5

API updates / refactoring

  • handle standard repositories and mirror ones the same way (remove bits of code relying on directory listings, which usually miss files on mirrors, #899)

  • rework artifact handling methods, wipe some hacks they were relying on (#902)

  • replace a few String types in the API by tagged types (#902)

  • rework CLI source code (remove dependency on scalaz, make the resolve command easier to test and re-use, #934)



  • CLI to publish artifacts

  • CLI to install applications

  • security / GPG-related features


(Formerly known as jupyter-scala)


  • add web site (#228)


  • try adding basic inspection capabilities (#234, #235)


  • maybe try to resume / revive an on-going effort, from a year ago, that aimed at making the various scala kernels for Jupyter converge

  • document the new / less known features of almond (spark UX related ones in particular)

SIP meetings

To read/watch more about the SIP:

  • September 2018 please go to: minutes or watch the meeting on Scala Center’s YouTube channel.

  • Next SIP meeting is taking place on the 22nd October 2018 at 5 PM CEST, please join and comment live on our Channel.

  • Beginning of November the SIP Committee is meeting face-to-face at EPFL, Lausanne, Switzerland to discuss many future changes in 3-day long gathering. We are working on a program and how to include the community in live streams at certain points in the day. Stay tuned, more info coming soon.