Drop most explicit self types in the standard library

They were causing cycles before. With the new policy these types don't need
to be given explicitly anymore.

I verified that the simple "Option" test now compiles.

Fixes #19398

Author: odersky

scala2-library-cc/src/scala/collection/IndexedSeqView.scala

@@ -55,7 +55,6 @@ object IndexedSeqView {
 
   @SerialVersionUID(3L)
   private[collection] class IndexedSeqViewIterator[A](self: IndexedSeqView[A]^) extends AbstractIterator[A] with Serializable {
-    this: IndexedSeqViewIterator[A]^ =>
     private[this] var current = 0
     private[this] var remainder = self.length
     override def knownSize: Int = remainder
@@ -90,7 +89,6 @@ object IndexedSeqView {
   }
   @SerialVersionUID(3L)
   private[collection] class IndexedSeqViewReverseIterator[A](self: IndexedSeqView[A]^) extends AbstractIterator[A] with Serializable {
-    this: IndexedSeqViewReverseIterator[A]^ =>
     private[this] var remainder = self.length
     private[this] var pos = remainder - 1
     @inline private[this] def _hasNext: Boolean = remainder > 0

scala2-library-cc/src/scala/collection/Iterable.scala

@@ -9,7 +9,6 @@
  * See the NOTICE file distributed with this work for
  * additional information regarding copyright ownership.
  */
-
 package scala
 package collection
 
@@ -29,7 +28,6 @@ import language.experimental.captureChecking
 trait Iterable[+A] extends IterableOnce[A]
   with IterableOps[A, Iterable, Iterable[A]]
   with IterableFactoryDefaults[A, Iterable] {
-  this: Iterable[A]^ =>
 
   // The collection itself
   @deprecated("toIterable is internal and will be made protected; its name is similar to `toList` or `toSeq`, but it doesn't copy non-immutable collections", "2.13.7")
@@ -134,7 +132,6 @@ trait Iterable[+A] extends IterableOnce[A]
   *  and may be nondeterministic.
   */
 trait IterableOps[+A, +CC[_], +C] extends Any with IterableOnce[A] with IterableOnceOps[A, CC, C] {
-  this: IterableOps[A, CC, C]^ =>
 
   /**
     * @return This collection as an `Iterable[A]`. No new collection will be built if `this` is already an `Iterable[A]`.

scala2-library-cc/src/scala/collection/IterableOnce.scala

@@ -43,7 +43,6 @@ import language.experimental.captureChecking
   * @define coll collection
   */
 trait IterableOnce[+A] extends Any {
-  this: IterableOnce[A]^ =>
 
   /** Iterator can be used only once */
   def iterator: Iterator[A]^{this}

scala2-library-cc/src/scala/collection/Iterator.scala

@@ -1302,5 +1302,4 @@ object Iterator extends IterableFactory[Iterator] {
 }
 
 /** Explicit instantiation of the `Iterator` trait to reduce class file size in subclasses. */
-abstract class AbstractIterator[+A] extends Iterator[A]:
-  this: Iterator[A]^ =>
+abstract class AbstractIterator[+A] extends Iterator[A]

scala2-library-cc/src/scala/collection/Map.scala

@@ -104,7 +104,6 @@ trait Map[K, +V]
 trait MapOps[K, +V, +CC[_, _] <: IterableOps[_, AnyConstr, _], +C]
   extends IterableOps[(K, V), Iterable, C]
     with PartialFunction[K, V] {
-  this: MapOps[K, V, CC, C]^ =>
 
   override def view: MapView[K, V]^{this} = new MapView.Id(this)
 

scala2-library-cc/src/scala/collection/MapView.scala

@@ -21,7 +21,6 @@ import caps.unsafe.unsafeAssumePure
 trait MapView[K, +V]
   extends MapOps[K, V, ({ type l[X, Y] = View[(X, Y)] })#l, View[(K, V)]]
     with View[(K, V)] {
-  this: MapView[K, V]^ =>
 
   override def view: MapView[K, V]^{this} = this
 
@@ -191,6 +190,5 @@ trait MapViewFactory extends collection.MapFactory[({ type l[X, Y] = View[(X, Y)
 
 /** Explicit instantiation of the `MapView` trait to reduce class file size in subclasses. */
 @SerialVersionUID(3L)
-abstract class AbstractMapView[K, +V] extends AbstractView[(K, V)] with MapView[K, V]:
-  this: AbstractMapView[K, V]^ =>
+abstract class AbstractMapView[K, +V] extends AbstractView[(K, V)] with MapView[K, V]
 

scala2-library-cc/src/scala/collection/Stepper.scala

@@ -39,7 +39,6 @@ import scala.collection.Stepper.EfficientSplit
   * @tparam A the element type of the Stepper
   */
 trait Stepper[@specialized(Double, Int, Long) +A] {
-  this: Stepper[A]^ =>
 
   /** Check if there's an element available. */
   def hasStep: Boolean
@@ -186,7 +185,6 @@ object Stepper {
 
 /** A Stepper for arbitrary element types. See [[Stepper]]. */
 trait AnyStepper[+A] extends Stepper[A] {
-  this: AnyStepper[A]^ =>
 
   def trySplit(): AnyStepper[A]
 
@@ -258,7 +256,6 @@ object AnyStepper {
 
 /** A Stepper for Ints. See [[Stepper]]. */
 trait IntStepper extends Stepper[Int] {
-  this: IntStepper^ =>
 
   def trySplit(): IntStepper
 
@@ -298,7 +295,6 @@ object IntStepper {
 
 /** A Stepper for Doubles. See [[Stepper]]. */
 trait DoubleStepper extends Stepper[Double] {
-  this: DoubleStepper^ =>
   def trySplit(): DoubleStepper
 
   def spliterator[B >: Double]: Spliterator.OfDouble^{this} = new DoubleStepper.DoubleStepperSpliterator(this)
@@ -338,7 +334,6 @@ object DoubleStepper {
 
 /** A Stepper for Longs. See [[Stepper]]. */
 trait LongStepper extends Stepper[Long] {
-  this: LongStepper^ =>
 
   def trySplit(): LongStepper^{this}
 

scala2-library-cc/src/scala/collection/View.scala

@@ -24,7 +24,6 @@ import language.experimental.captureChecking
   * @define Coll `View`
   */
 trait View[+A] extends Iterable[A] with IterableOps[A, View, View[A]] with IterableFactoryDefaults[A, View] with Serializable {
-  this: View[A]^ =>
 
   override def view: View[A]^{this} = this
 

scala2-library-cc/src/scala/collection/WithFilter.scala

@@ -23,7 +23,6 @@ import language.experimental.captureChecking
   */
 @SerialVersionUID(3L)
 abstract class WithFilter[+A, +CC[_]] extends Serializable {
-  this: WithFilter[A, CC]^ =>
 
   /** Builds a new collection by applying a function to all elements of the
     * `filtered` outer $coll.

scala2-library-cc/src/scala/collection/immutable/Iterable.scala

@@ -25,8 +25,6 @@ import language.experimental.captureChecking
 trait Iterable[+A] extends collection.Iterable[A]
                       with collection.IterableOps[A, Iterable, Iterable[A]]
                       with IterableFactoryDefaults[A, Iterable] {
-  this: Iterable[A]^ =>
-
   override def iterableFactory: IterableFactory[Iterable] = Iterable
 }
 

scala2-library-cc/src/scala/collection/immutable/LazyListIterable.scala

@@ -251,7 +251,6 @@ final class LazyListIterable[+A] private(private[this] var lazyState: () => Lazy
     with IterableOps[A, LazyListIterable, LazyListIterable[A]]
     with IterableFactoryDefaults[A, LazyListIterable]
     with Serializable {
-  this: LazyListIterable[A]^ =>
   import LazyListIterable._
 
   @volatile private[this] var stateEvaluated: Boolean = false
@@ -964,7 +963,6 @@ object LazyListIterable extends IterableFactory[LazyListIterable] {
   private[this] val _empty = newLL(State.Empty).force
 
   private sealed trait State[+A] extends Serializable {
-    this: State[A]^ =>
     def head: A
     def tail: LazyListIterable[A]^
   }
@@ -1252,7 +1250,6 @@ object LazyListIterable extends IterableFactory[LazyListIterable] {
 
   private class SlidingIterator[A](private[this] var lazyList: LazyListIterable[A]^, size: Int, step: Int)
     extends AbstractIterator[LazyListIterable[A]] {
-    this: SlidingIterator[A]^ =>
     private val minLen = size - step max 0
     private var first = true
 
@@ -1273,7 +1270,6 @@ object LazyListIterable extends IterableFactory[LazyListIterable] {
 
   private final class WithFilter[A] private[LazyListIterable](lazyList: LazyListIterable[A]^, p: A => Boolean)
     extends collection.WithFilter[A, LazyListIterable] {
-    this: WithFilter[A]^ =>
     private[this] val filtered = lazyList.filter(p)
     def map[B](f: A => B): LazyListIterable[B]^{this, f} = filtered.map(f)
     def flatMap[B](f: A => IterableOnce[B]^): LazyListIterable[B]^{this, f} = filtered.flatMap(f)
@@ -1320,7 +1316,6 @@ object LazyListIterable extends IterableFactory[LazyListIterable] {
 
   private object LazyBuilder {
     final class DeferredState[A] {
-      this: DeferredState[A]^ =>
       private[this] var _state: (() => State[A]^) @uncheckedCaptures = _
 
       def eval(): State[A]^ = {

scala2-library-cc/src/scala/collection/mutable/CheckedIndexedSeqView.scala

@@ -16,7 +16,6 @@ package mutable
 import language.experimental.captureChecking
 
 private[mutable] trait CheckedIndexedSeqView[+A] extends IndexedSeqView[A] {
-  this: CheckedIndexedSeqView[A]^ =>
 
   protected val mutationCount: () => Int
 

scala2-library-cc/src/scala/collection/mutable/Iterable.scala

@@ -19,7 +19,6 @@ trait Iterable[A]
   extends collection.Iterable[A]
     with collection.IterableOps[A, Iterable, Iterable[A]]
     with IterableFactoryDefaults[A, Iterable] {
-  this: Iterable[A]^ =>
 
   override def iterableFactory: IterableFactory[Iterable] = Iterable
 }
@@ -33,5 +32,4 @@ trait Iterable[A]
 object Iterable extends IterableFactory.Delegate[Iterable](ArrayBuffer)
 
 /** Explicit instantiation of the `Iterable` trait to reduce class file size in subclasses. */
-abstract class AbstractIterable[A] extends scala.collection.AbstractIterable[A] with Iterable[A]:
-  this: AbstractIterable[A]^ =>
+abstract class AbstractIterable[A] extends scala.collection.AbstractIterable[A] with Iterable[A]