Quickfix unexpected edits in method types with params but inferred result

[som-snytt]

Reproduction steps

Scala version: 2.13.12 (head)

import scala.collection.{IntStepper, Stepper}

abstract class Stepper1[A] extends Stepper[A] {
  var hasStep = true
  override def estimateSize = if (hasStep) 1 else 0
  override def characteristics = 0
  override def trySplit() = null
}
trait PrimitiveStepper1[A] extends Stepper1[A] {
  override def spliterator[B >: A] = ???
  override def javaIterator[B >: A] = ???
}

Problem

Using

// scalac: -Xsource:3 -Xlint -quickfix:cat=scala3-migration

diff is not legal code.

diff --git a/test/files/run/stepper.scala b/test/files/run/stepper.scala
index af96c6613f..ac55f52275 100644
--- a/test/files/run/stepper.scala
+++ b/test/files/run/stepper.scala
@@ -8,11 +8,11 @@ abstract class Stepper1[A] extends Stepper[A] {
   var hasStep = true
   override def estimateSize = if (hasStep) 1 else 0
   override def characteristics = 0
-  override def trySplit() = null
+  override def trySplit: Null() = null
 }
 trait PrimitiveStepper1[A] extends Stepper1[A] {
-  override def spliterator[B >: A] = ???
-  override def javaIterator[B >: A] = ???
+  override def spliterator: Nothing[B >: A] = ???
+  override def javaIterator: Nothing[B >: A] = ???
 }
 class IntStepper1(elem: Int) extends Stepper1[Int] with IntStepper with PrimitiveStepper1[Int] {
   override def nextStep() = {

It would be nice if I can apply edits to see the new inferred types, instead of the old inferred types, since I am migrating to 3. That is an alternative to silencing the warnings.

via the forum

[SethTisue]

fyi @lrytz

[xuwei-k]

another example

trait A {
  def f[B, C](c: C): Either[B, C]
}

object A {
  val x = new A {
    def f[B, C](c: C) = Right(c)
  }
}

   val x = new A {
-    def f[B, C](c: C) = Right(c)
+    def f: scala.util.Right[Nothing,C][B, C](c: C) = Right(c)
   }

[eed3si9n]

Given the emerging class of quickfixes errors, maybe we should create a documentation that lists current set of quickfixes that are enabled in the compiler(s) so we can identify which fix can be causing the problem in addition to fixing things.

[lrytz]

Fixed in https://github.com/scala/scala/pull/10559

[som-snytt]

I started a list of behaviors under -Xsource:help, I'll also try -quickfix:help. That is my last idea before sleep.