Metals 

 Scala 3 and Metals - a match made in heaven

Tomasz Godzik

Agenda 

1. Introduction 

2. metals - What is it?

3. build tools

4. Scala 3 compiler

5. Current Scala 3 features

6. Optional braces improvements

7. Some demos

8. Recent work

9. Questions

Why am I Here?

Why am I Here?

Why am I Here?

Why am I Here?

Currently working on Metals as one of the main contributors as a part of the collaboration between VirtusLab and Scala Center.

Who Contributed to what metals is today?

What is metals

created by Ólafur Páll Geirsson while working at scala center

SCALAMETA + LS

not your standard IDE

WORKS DIRECTLY WITH THE BUILD TOOL

uses WIDELY ADAPTED LSP PROTOCOL

uses LSP + extensions to provide support in any editor

focus on the language support

Your favourite language in you favourite Editor

Build tools

Build tools

The universe of Build tools

Mill

The universe of Build tools

Mill

Metals

The universe of Build tools

Metals

Mill

The build server protocol

single instance running on your machine

Jited Scala compiler

uses zinc incremental compiler

worked on by the same team as Metals

Bloop

recently updated to newest zinc

a number of Scala 3 issues fixed

should work well with all the  supported tools

Bloop

Standalone build server

numerous ways of using the build tools

using Bloop from generated configuration

- can generate configuration files for Bloop Build server

- standalone server <- probably best supported aside Bloop

- supports Scala 3

Mill

- can generate configuration files for Bloop Build server

- standalone server

- SUPPORTS SCALA 3

- can generate configuration files for Bloop Build server

- fastest config generation

- SUPPORTS SCALA 3

- can generate configuration files for Bloop Build server

- SUPPORTS SCALA 3 from 7.3 version

- can generate configuration files for Bloop Build server

- SUPPORTS SCALA 3 from 7.3 version

- also updated Zinc support in gradle 7.5!

GET STARTED WITH scala 3

https://scala-cli.virtuslab.org/

New CLI tool to work with Scala

Not only 3! 

Support for Native and JS

Seamless, friction less experience

DEMO!

https://scala-cli.virtuslab.org/

SCALA 3 COMPILER

Interactive features

things that need to work with broken  code

new challenges related to optional braces

hover/definition/completions/selection etc.

Presentation compiler

not your usual compiler

main difference is that it allows for errors

run until the typer

reimplemented for Scala 3

used initially for the Dotty language server

Presentation compiler

or why it's a match made in heaven

constant COOPERATION with the compiler team

pushing fixes into to the compiler 

the compiler team helps out fixing their own  

Great help from Martin Odersky!

well tested and fast to deploy

Support for each new Scalaversion available before announcement

we are Testing nightlies

And we add support for all the most recent nightlies in the prerelease version

History of one fix

This is a lot of help

fixes both issues with error reporting and presentation compiler

close broken code in a smaller leaf

we can ignore that leaf

Before the fix

after the fix

the future

we are still ironing things out

Report any issues you encounter

You can also finding existing ones in Metals with Scala 3 label or in dotty with area:ide label

the future continued

better support of multiple non compiling files?

numerous ideas

probably start with Scala 3

Scala 3 features

Current Scala 3 features

if something is not working it means we are working on it!

Interactive features

completions

New completions:

•  keyword completions

• named argument completions

• scope completions in an empty line

• match types!

incoming

• override completions

• scaladocs

• better signature help

hover

• proper scaladocs shown

• from parent if needed

• correct shown in for comprehensions

• properly shown extension methods

• expression type on selection

Definition

uses information from semanticdb generated during compilation

fallback uses the compiler

index features

index features

they require full compilation for semanticdb to be produced

information provided by the build tool

special flag for Scala 3 

New support for decorations in Scala 3!

References

uses semanticdb

needs compilation

responsive

Renames

uses semanticdb

needs compilation

will rename all symbol overrides

code lenses

test explorer

go to implementation

type decorations

implicit parameters, classes, conversions

A lot more

dEMOS

Demos

SOME OF THE FEATURES might be AVAILABLE IN NIGHTIES

you can chose to use prerelease version

Might break from time to time

Metals analyse

Can be used to:

• decompile classfiles

• show tasty

• show semanticb

• show javap

User experience improvements

• simpler launching of programs

• better doctor

• more feedback for the user to show what is going on

• lots more to improve!

test explorer

• see all your tests with an ability to filter

• run a subset of tests

• better UX of matching results to tests

• constantly improved

better library explorer

• not yet merged

• amazing work by Arthur McGibbon

• virtual docs with breadcrumbs

• easy way to navigate your dependencies

• navigation and all other features working

• automatic decompilation

Scala 3 debugger

• still worked on

• might be moved to the compiler

• great work by @tdudzik

• also working completions!

Bonus demo?

Bonus demo?

Recent Work

- improved doctor

- create companion object

- better unapply signatures

- bloop settings

- better support for munit in test explorer

- improvements for Scala 3 support

NEWEST Metals FEATURES

https://scalameta.org/metals/blog/2022/04/26/aluminium

What do we need to work on

more completions!

incremental improvements

better support between multiple non compiling files

Don't hestitate to sent us ideas

https://github.com/scalameta/metals-feature-requests

We do listen!

https://github.com/scalameta/metals-feature-requests

Related Talks

QUESTIONS?