wrong number of arguments at getClass for (): PackratParsers

[chungonn]

The code fragment compiles on scala 2.13.1 but not on dotty 0.24.0-RC1,

Minimized code

package test

import scala.util.parsing.combinator.{ImplicitConversions, PackratParsers, RegexParsers}

class TestParser  extends RegexParsers with ImplicitConversions with PackratParsers {

}

Output

[info] Compiling 2 Scala sources to /home/chungonn/development/scala3/bugs/packratparsers/target/scala-0.24/classes ...
[error] -- Error: /home/chungonn/development/scala3/bugs/packratparsers/src/main/scala/test/TestParser.scala:5:83 
[error] 5 |class TestParser  extends RegexParsers with ImplicitConversions with PackratParsers {
[error]   |                                                                                   ^
[error]   |wrong number of arguments at getClass for (): PackratParsers.this.MemoEntry$: (PackratParsers.this.MemoEntry$#<init> : (): PackratParsers.this.MemoEntry$), expected: 0, found: 1
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 3 s, completed 1 May, 2020 9:37:08 AM

Expectation

[griggt]

Standalone reproducer below.

Note that this is a Scala 2 interop issue, and only occurs when the trait is compiled by Scala 2 and extended in a file compiled by Scala 3.

lib/lib.scala

package i8847

trait P {
  // The `private` modifier is needed, and `X` must be a case class or case object
  private case class X(x: Int)
  // private case object X
}

main/test.scala

import i8847.P

class T extends P

build.sbt

lazy val lib = (project in file ("lib"))
  .settings(scalaVersion := "2.13.3")

lazy val main = (project in file ("main"))
  .dependsOn(lib)
  .settings(
    scalaVersion := "0.24.0-RC1",
    projectDependencies := {
      projectDependencies.value.map(_.withDottyCompat(scalaVersion.value))
    }
  )

Output from Dotty 0.24.0-RC1

[info] Compiling 1 Scala source to /src/dotty-issues/i8847/lib/target/scala-2.13/classes ...
[info] Done compiling.
[info] Compiling 1 Scala source to /src/dotty-issues/i8847/main/target/scala-0.24/classes ...
[error] -- Error: /src/dotty-issues/i8847/main/test.scala:3:17 -----------------------------------
[error] 3 |class T extends P
[error]   |                 ^
[error]   |wrong number of arguments at getClass for (): P.this.X$: (P.this.X$#<init> : (): P.this.X$), expected: 0, found: 1
[error] one error found
[error] (main / Compile / compileIncremental) Compilation failed

This is fixed by #8652.

[griggt]

While creating a standalone reproducer from the original and bisecting this issue, I ran into another:

lib.scala

package i8847

trait Foo {
  def foo(): Unit = ???
}

trait Bar extends Foo {
  override def foo(): Unit = super.foo()
}

trait Baz extends Foo {
  override def foo(): Unit = super.foo()
}

test.scala

import i8847.{ Bar, Baz }

class C extends Bar with Baz

$ scalac -version
Scala compiler version 2.13.3 -- Copyright 2002-2020, LAMP/EPFL and Lightbend, Inc.

$ scalac lib.scala

$ dotc -version
Dotty compiler version 0.26.0-bin-SNAPSHOT-git-d7bea54 -- Copyright 2002-2020, LAMP/EPFL

$ dotc test.scala
-- [E120] Naming Error: test.scala:3:6 -----------------------------------------
3 |class C extends Bar with Baz
  |      ^
  |      Double definition:
  |      private def super$foo(): Unit in class C and
  |      private def super$foo(): Unit in class C
  |      have the same type after erasure.
1 error found

This issue appears to have been both introduced and corrected during the commit sequence of #8652.