Tooling for scala 3
Dotty support in Metals
Tomasz Godzik
Some fun new concepts
Besides:
- simplified pattern matching
- better macros
- enums
- focus on ease of migration
- implicit suggestions
- a lot of even more modern features
THE FUTURE OR SCALA 3
trait A:
def f: Int
class C(x: Int) extends A:
def f = x
object O:
def f = 3Optional braces
val x: String = ???
val y: String | Null = ???
x == null // error
x eq null // error
"hello" == null // error
y == null // ok
y == x // okexplicit nulls
@main def helloWorld(
age: Int,
name: String,
others: String*
) = {
println(s"Hello $name!")
println(s"You are $age years old")
}outer methods
case class Circle(
x: Double,
y: Double,
radius: Double
)
def (c: Circle).circumference: Double =
c.radius * math.Pi * 2Extension methods
scalameta parser
- basis for a number of developer's tools
- works without the compiler
- fast
- has an easily understandable AST
- a lot projects depending on it
extension (c: Circle)
def shapeName = "Circle"Source(
stats = List(
Defn.ExtensionGroup(
eparam = Term.Param(
mods = List(),
name = Term.Name(value = "c"),
decltpe = Some(value = Type.Name(value = "Circle")),
default = None
),
tparams = List(),
uparams = List(),
body = Defn.Def(
mods = List(),
name = Term.Name(value = "shapeName"),
tparams = List(),
paramss = List(),
decltpe = None,
body = Lit.String(value = "Circle")
)
)
)
)
scalameta parser
enum ListEnum {
enum ListEnum[+A] {
case Cons(h: A, t: ListEnum[A])
case Empty
}
}
Document outline
Worksheets
scalameta parser
Parser Scala when used with the scala3 dialect
optional braces support
all the new features supported
scalameta parser
scala.meta.parser.dotty.CommunityDottySuite:
From https://github.com/lampepfl/dotty
a0707985bf..1f503e7868 master -> origin/master
e8cfbb381f..45b8dc0f9e release-3.0.0 -> origin/release-3.0.0
HEAD is now at 13de192d04 Merge pull request #11958 from lampepfl/derived-names-mac
--------------------------
dotty
Files parsed correctly 828
Files errored: 0
Time taken: 14989ms
Lines parsed: ~190k
Parsing speed per 1k lines ===> 78 ms/1klines
--------------------------
+ community-build-dotty 17.179sscalafmt
- important to keep consistent style for a team
- runs on CI
- can be considered a blocker to Scala 3 migration
object Main:
def main(args: Array[String]) =
val name: Option[String] = Some("AVeryLongString")
name
match
case None => println("Hello <unknown>")
case Some(x) => println(s"Hello $x")
object Main:
def main(args: Array[String]) =
val name: Option[String] =
Some("AVeryLongString")
name
match
case None => println("Hello <unknown>")
case Some(x) => println(s"Hello $x")
scalafmt
version = 3.0.0-RC1
runner.dialect = scala3
indent.main = 3scalafmt
version = 3.0.0-RC1
fileOverride {
"glob:**/scala-3*/**" {
runner.dialect = scala3
indent.main = 3
}
}scalafmt
def hello(name: String): Unit = {
val greeting = s"Hello $name"
println(greeting)
}Rewrite - drop braces
def hello(name: String): Unit =
val greeting = s"Hello $name"
println(greeting)
scalafmt
import scala.meta.{Main => Metals}
import scala.meta._
object Main{}Rewrite - New syntax
import scala.meta.Main as Metals
import scala.meta.*
object Main{}mdoc
```scala mdoc
val x = 1
val y = 2
x + y
``````scala
val x = 1
// x: Int = 1
val y = 2
// y: Int = 2
x + y
// res0: Int = 3
```after
Before
mdoc
```scala mdoc:crash
val y = ???
``````scala
val y = ???
// scala.NotImplementedError: an implementation is missing
// at scala.Predef$.$qmark$qmark$qmark(Predef.scala:288)
// at repl.MdocSession$App$$anonfun$1.apply$mcV$sp(modifiers.md:9)
// at repl.MdocSession$App$$anonfun$1.apply(modifiers.md:8)
// at repl.MdocSession$App$$anonfun$1.apply(modifiers.md:8)
```after
Before
mdoc
```scala mdoc:scalafmt
indent.callSite = 2
---
function(
argument1, // indented by 2
""
)
``````scala formatted
function(
argument1, // indented by 2
""
)
```
```scala original
function(
argument1, // indented by 2
""
)
```
<details class='config' open><summary>Config for this example:</summary><p>
```scala config
continuationIndent.callSite = 2
```
</p></details>after
Before
mdoc
scaladoc
Typechecked scaladoc snippets
```scala sc:failing
val iAmWrong: Int = 2.3
for(i ← 1.to(10))
yield i*2
```Borrows ideas and code from mdoc
But inside the compile
scalafix
import scala.List
import scala.collection.{immutable, mutable}
object Foo { immutable.Seq.empty[Int] }import scala.collection.immutable
object Foo { immutable.Seq.empty[Int] }before
after
scalafix
scalafix
import scala.meta._
import scala.collection.{mutable => mut}
object Main {}import scala.meta.*
import scala.collection.mutable as mut
object Main {}before
after
Your favourite language in you favourite Editor
Metals
Scala 3 support
Metals
Scala 3 Inline
Metals
inline def power(x: Double, n: Int): Double =
if n == 0 then 1.0
else if n == 1 then x
else
val y = power(x, n / 2)
if n % 2 == 0 then y * y else y * y * xScala 3 auto importing implicits
Metals
Tasty!
Metals
+-------------+ +-------------+ +-------------+
$ scalac | Hello.scala | -> | Hello.tasty | -> | Hello.class |
+-------------+ +-------------+ +-------------+
^ ^ ^
| | |
Your source TASTy file Class file
code for scalac for the JVM
(contains (incomplete
complete information)
information)MAcros
Metals
import scala.quoted.*
inline def assert(inline expr: Boolean): Unit =
${ assertImpl('expr) }
def assertImpl(expr: Expr[Boolean])(using Quotes) = '{
if !$expr then
throw AssertionError(s"failed assertion: ${${ showExpr(expr) }}")
}
def showExpr(expr: Expr[Boolean])(using Quotes): Expr[String] =
'{ "<some source code>" } // Better implementation later in this documentScalaJS
ScalaJS
currently Implemented inside Scala 3 compiler
reuses most of existing code
Implemented in 3 months!
not outstanding issues
Scala native
Scala native
Windows support
multithreading
scala 3
Scala 3 will be amazing!
