Generated bridge clashes with member of trait in Scala.js under Scala 3

[Rich2]

Scala 3.0.2-RC1 (And Scala 2.13.6)

I've attempted to minimise the code, but haven't been able to reproduce the bug in simplified code. I have therefore created a cut down repository here from my main repository with the minimum 2 modules required to produce the errors.

The code compiles for Jvm but is failing for Scala.js. There are 2 modules Util and Graphics. Util compiles under all 4 combinations of Js and jvm targets and Scala 2.13.6 and Scala 3.0.2-RC1. The graphics module fails for Scala.js on Scala 3 implicit lookup succeeds for JVM but fails for Js. In Sbt:

graphicsJvm2/compile //compiles
graphicsJvm3/compile //compiles
graphicsJs2/compile //compiles
graphicsJs3/compile //gives the following errors

sbt:jvmjs> graphicsJs3/compile
[info] compiling 177 Scala sources to /Common/jvmjs/graphicsJs3/target/scala-3.0.2-RC1/classes ...
[error] -- Error: /Common/jvmjs/srcGraphics/Trans/ProlignMatrix.scala:48:50 ------------
[error] 48 |    (arrA : Arr[A], prolignMatrix: ProlignMatrix) => arrA.map(a => ev.prolignObj(a, prolignMatrix))
[error]    |                                                  ^
[error]    |bridge generated for member method prolignObj(arrA: ostrat.Arr[A], prolignMatrix: ostrat.geom.ProlignMatrix): ostrat.Arr[A] in anonymous class Object with ostrat.geom.Prolign {...}
[error]    |which overrides method prolignObj(obj: A, prolignMatrix: ostrat.geom.ProlignMatrix): A in trait Prolign
[error]    |clashes with definition of the member itself; both have erased type (arrA: Object, prolignMatrix: ostrat.geom.ProlignMatrix): Object."
[error] -- Error: /Common/jvmjs/srcGraphics/Trans/Slate.scala:28:84 --------------------
[error] 28 |  implicit def arrImplicit[A](implicit ev: Slate[A]): Slate[Arr[A]] = (obj, dx, dy) => obj.smap(ev.SlateXYT(_, dx, dy))
[error]    |                                                                                    ^
[error]    |bridge generated for member method SlateXYT(obj: ostrat.Arr[A], dx: Double, dy: Double): ostrat.Arr[A] in anonymous class Object with ostrat.geom.Slate {...}
[error]    |which overrides method SlateXYT(obj: T, xDelta: Double, yDelta: Double): T in trait Slate
[error]    |clashes with definition of the member itself; both have erased type (obj: Object, dx: Double, dy: Double): Object."
[error] two errors found
[error] two errors found
[error] (graphicsJs3 / Compile / compileIncremental) Compilation failed
[error] Total time: 19 s, completed 22 Jul 2021, 09:13:01

Expectation is that the compile phase will be the same for Jvm and Js and also what compiles for Scala 2 will compile for Scala 3.

[Kordyjan]

A smaller, single file, example, that passes on jvm but fails on js:

import reflect.ClassTag
import annotation._, unchecked.uncheckedVariance

final class Arr[+A](val unsafeArr: Array[A] @uncheckedVariance) extends AnyVal {
   def map[B](f: A => B): Arr[B] = ???
}

trait Prolign[A] {
  def prolignObj(obj: A, i: Int): A
}

object Prolign {
  implicit def arrImlicit[A](implicit ct: ClassTag[A], ev: Prolign[A]): Prolign[Arr[A]] =
    (arrA: Arr[A], i: Int) => arrA.map(a => ev.prolignObj(a, i))
}

I'll try to minimize it further.

[Kordyjan]

Minimal example, that passes when compiled to jvm but fails with js:

trait A[T]:
  def doA(arg1: T): T

class B[T](val arr: Array[T]) extends AnyVal

def a[T]: A[B[T]] =
  (arg1: B[T]) => null.asInstanceOf[B[T]]

It is worth noting that extends AnyVal is necessary here.

[sjrd]

I'm on mobile right now, so I can't test. But I'm pretty sure this is not directly related to Scala.js, but rather to the fact that the SAM type is not a platform SAM type. I guess it can be reproduced on the JVM by using a SAM type that is not a JVM SAM type. For example:

class C

trait A[T] extends C:
// The rest as before

[smarter]

In which this is likely a duplicate of #11264

[Kordyjan]

I'm on mobile right now, so I can't test. But I'm pretty sure this is not directly related to Scala.js, but rather to the fact that the SAM type is not a platform SAM type. I guess it can be reproduced on the JVM by using a SAM type that is not a JVM SAM type. For example:

class C

trait A[T] extends C:
// The rest as before

Confirmed, so it is unrelated to js.