Metals

your IDE FOR SCALA 3

Tomasz Godzik

Agenda

1. Introduction

2. BASIC FEATURES.

3. GETTING STARTED WITH SCALA 3

4. Demo

5. Advanced features

6. BSP AND LSP

7. Recent work

8. Upcoming work

9. Questions!

Questions!

Please ask in the Q&A!

Will try to answer all at the end.

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?

Metals - Scala (3) language server with rich ide features

Your favourite language in you favourite Editor

tooling

- Scala is not just the compiler

- it's the whole tooling ecosystem

- Proper IDE is important for users to pick up the language

Tooling

- coordinating efforts with the compiler team

- each Scala 3 compiler release is synced with Metals

- upstream fixes to the compiler

Scala 3 support

- Based on Dotty language server

- evolved heavily since then

- we still depends on the compiler itself

completions

most of the existing functionality on par with Scala 2

Improved with each release

hover

information shown when mouse over symbol

additional Scala 3 specific info - extension methods and enums

Definition

uses information from semanticdb generated during compilation

fallback uses the compiler

References

uses semanticdb

needs compilation

responsive

Renames

uses semanticdb

needs compilation

will rename all symbol overrides

GET STARTED WITH scala3

Via coursier

> cs install giter8
> g8 scala/scala3.g8
> cd dotty
> code .

VIA NEW PROJECT WIZARD

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/

in an online IDE

1. go to https://GITHUB.COM/TGODZIK/CREATIVE-SCALA

2. Click on the first link available

or

Just use the ready link:

https://gitpod.io/#https://github.com/tgodzik/creative-scala

in an online IDE

You can also join me in my workspace!

https://indigo-ptarmigan-67ssord3.ws-eu17.gitpod.io

Let's try to use doodle to create a shape mosaic from all the people

Advanced features

run/debug

run and debug your scala 3 programs

you can use the new @main annotation

via lenses, launch.json or special commands

EXPRESSION EVALUATION STILL WORKED ON

scalameta.org/metals/docs/editors/vscode

Pasting code

automatically fix indentation when copy pasting

based on the current indentation at paste

additional setting

metals.enableIndentOnPaste

still experimental

scalafmt support

metals will automatically set up .scalafmt.conf file

it will make sure a proper dialect is used for each source root

always most recent version

version = "3.0.5"
runner.dialect = scala212
fileOverride {
  "glob:**/tests/input3/src/main/scala/**" {
     runner.dialect = scala3
  }
  "glob:**/mtags/target/target3/scala-3.1.0/src_managed/main/**" {
     runner.dialect = scala3
  }
  "glob:**/mtags/src/main/scala-3/**" {
     runner.dialect = scala3
  }
}

Organize imports

works for all Scala 3 code except given imports

fix available in the next release

works with unsaved code

can be configured to work on CI

works with defaults

no unused imports

Additional decorations

Starting with 3.1.0 -> type decorations!

can be turned on via toggle or in settings

great work by Rikito Taniguchi in the compiler

source file analyzer

Different ways to view your Scala files:

- javap

- semanticdb

- tasty

- soon java decompiler

worksheets

- allow you to quickly experiment with the language and workspace

- can work with source or totally independently

- powered by mdoc

The language server protocol

How does it work

Client Editor

LSP Server

How does it work

Client Editor

LSP Server

object Main{
  def adding(a : Int, b : Int) = a + b
  val additional = ""
  val one = 1
  val two = 2
  addi_
}

How does it work

Client Editor

LSP Server

Completions

object Main{
  def adding(a : Int, b : Int) = a + b
  val additional = ""
  val one = 1
  val two = 2
  addi_
}

How does it work

Client Editor

LSP Server

Completions

object Main{
  def adding(a : Int, b : Int) = a + b
  val additional = ""
  val one = 1
  val two = 2
  addi_
}

How does it work

Client Editor

LSP Server

object Main{
  def adding(a : Int, b : Int) = a + b
  val additional = ""
  val one = 1
  val two = 2
  addi_
}

How does it work

Client Editor

LSP Server

- adding()

- additional

object Main{
  def adding(a : Int, b : Int) = a + b
  val additional = ""
  val one = 1
  val two = 2
  addi_
}

How does it work

Client Editor

LSP Server

- adding()

- additional

object Main{
  def adding(a : Int, b : Int) = a + b
  val additional = ""
  val one = 1
  val two = 2
  addi_
}

How does it work

Client Editor

LSP Server

object Main{
  def adding(a : Int, b : Int) = a + b
  val additional = ""
  val one = 1
  val two = 2
  addi_
}

How does it work

Client Editor

LSP Server

object Main{
  def adding(a : Int, b : Int) = a + b
  val additional = ""
  val one = 1
  val two = 2
  adding(_)
}

The build server protocol

The universe of Build tools

Mill

The universe of Build tools

Mill

Metals

The universe of Build tools

Mill

Metals

- can generate configuration files for Bloop Build server

- standalone server

- 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

- SUPPORTS SCALA 3

- can generate configuration files for Bloop Build server

- SUPPORTS SCALA 3 from 7.3 version

BSP Server

LSP Server

How does it work?

BSP Server

LSP Server

What is this code a part of!

How does it work?

BSP Server

LSP Server

Which project?

How does it work?

BSP Server

LSP Server

Which project?

How does it work?

BSP Server

LSP Server

How does it work?

BSP Server

LSP Server

Project Foo

How does it work?

BSP Server

LSP Server

Project Foo

How does it work?

BSP Server

LSP Server

I don't know how to compile it!

How does it work?

BSP Server

LSP Server

Compile Foo!

How does it work?

BSP Server

LSP Server

Compile Foo!

How does it work?

BSP Server

LSP Server

How does it work?

BSP Server

LSP Server

Error report

How does it work?

BSP Server

LSP Server

Error report

How does it work?

BSP Server

LSP Server

Diagnostics

How does it work?

Recent Work

- expression evaluator (Scala 3 coming later)

- type on selection

- search text files in jars

- continuous Scala 3 improvements

NEWEST Metals FEATURES

https://scalameta.org/metals/blog/2021/10/26/tungsten

NEWEST Metals FEATURES

Quick look

What do we need to work on

Custom Completions

new Scala 3 specific completions

Expression evaluator for debugging

Some of the refactorings including `Implement all members`

Don't hestitate to sent us ideas