Drop all but one usages of @uncheckedCaptures from stdlib

Author: odersky

tests/pos-special/stdlib/collection/IterableOnce.scala

@@ -14,7 +14,7 @@ package scala
 package collection
 
 import scala.annotation.tailrec
-import scala.annotation.unchecked.{uncheckedVariance, uncheckedCaptures}
+import scala.annotation.unchecked.uncheckedVariance
 import scala.collection.mutable.StringBuilder
 import scala.language.implicitConversions
 import scala.math.{Numeric, Ordering}
@@ -1341,8 +1341,8 @@ object IterableOnceOps:
   // Moved out of trait IterableOnceOps to here, since universal traits cannot
   // have nested classes in Scala 3
   private class Maximized[X, B](descriptor: String)(f: X -> B)(cmp: (B, B) -> Boolean) extends AbstractFunction2[Maximized[X, B], X, Maximized[X, B]] {
-    var maxElem: X @uncheckedCaptures = null.asInstanceOf[X]
-    var maxF: B @uncheckedCaptures = null.asInstanceOf[B]
+    var maxElem: X  = null.asInstanceOf[X]
+    var maxF: B  = null.asInstanceOf[B]
     var nonEmpty = false
     def toOption: Option[X] = if (nonEmpty) Some(maxElem) else None
     def result: X = if (nonEmpty) maxElem else throw new UnsupportedOperationException(s"empty.$descriptor")

tests/pos-special/stdlib/collection/Iterator.scala

@@ -14,10 +14,9 @@ package scala.collection
 
 import scala.collection.mutable.{ArrayBuffer, ArrayBuilder, Builder, ImmutableBuilder}
 import scala.annotation.tailrec
-import scala.annotation.unchecked.{uncheckedVariance, uncheckedCaptures}
+import scala.annotation.unchecked.uncheckedVariance
 import scala.runtime.Statics
 import language.experimental.captureChecking
-import annotation.unchecked.uncheckedCaptures
 
 
 /** Iterators are data structures that allow to iterate over a sequence
@@ -161,12 +160,12 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
 
     require(size >= 1 && step >= 1, f"size=$size%d and step=$step%d, but both must be positive")
 
-    private[this] var buffer: Array[B @uncheckedCaptures] = null                 // current result
-    private[this] var prev: Array[B @uncheckedCaptures] = null                   // if sliding, overlap from previous result
+    private[this] var buffer: Array[B] = null                 // current result
+    private[this] var prev: Array[B] = null                   // if sliding, overlap from previous result
     private[this] var first = true                            // if !first, advancing may skip ahead
     private[this] var filled = false                          // whether the buffer is "hot"
     private[this] var partial = true                          // whether to emit partial sequence
-    private[this] var padding: () -> B @uncheckedCaptures = null // what to pad short sequences with
+    private[this] var padding: () -> B = null // what to pad short sequences with
     private[this] def pad = padding != null                   // irrespective of partial flag
     private[this] def newBuilder = {
       val b = ArrayBuilder.make[Any]
@@ -258,7 +257,7 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
       }
       // segment must have data, and must be complete unless they allow partial
       val ok = index > 0 && (partial || index == size)
-      if (ok) buffer = builder.result().asInstanceOf[Array[B @uncheckedCaptures]]
+      if (ok) buffer = builder.result().asInstanceOf[Array[B]]
       else prev = null
       ok
     }
@@ -417,8 +416,7 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
 
   @deprecated("Call scanRight on an Iterable instead.", "2.13.0")
   def scanRight[B](z: B)(op: (A, B) => B): Iterator[B]^{this} =
-    ArrayBuffer.from[A @uncheckedCaptures](this).scanRight(z)(op).iterator
-      // @uncheckedCaptures is safe since the ArrayBuffer is local temporrary storage
+    ArrayBuffer.from[A](this).scanRight(z)(op).iterator
 
   def indexWhere(p: A => Boolean, from: Int = 0): Int = {
     var i = math.max(from, 0)
@@ -561,7 +559,7 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
     */
   def distinctBy[B](f: A -> B): Iterator[A]^{this} = new AbstractIterator[A] {
 
-    private[this] val traversedValues = mutable.HashSet.empty[B @uncheckedCaptures]
+    private[this] val traversedValues = mutable.HashSet.empty[B]
     private[this] var nextElementDefined: Boolean = false
     private[this] var nextElement: A = _
 
@@ -704,7 +702,7 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
        */
       private[this] var status = 0
       private def store(a: A): Unit = {
-        if (lookahead == null) lookahead = new mutable.Queue[A @uncheckedCaptures]
+        if (lookahead == null) lookahead = new mutable.Queue[A]
         lookahead += a
       }
       def hasNext = {
@@ -867,8 +865,8 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
     *  @note   Reuse: $consumesOneAndProducesTwoIterators
     */
   def duplicate: (Iterator[A]^{this}, Iterator[A]^{this}) = {
-    val gap = new scala.collection.mutable.Queue[A @uncheckedCaptures]
-    var ahead: Iterator[A @uncheckedCaptures] = null // ahead is captured by Partner, so A is not recognized as parametric
+    val gap = new scala.collection.mutable.Queue[A]
+    var ahead: Iterator[A] = null // ahead is captured by Partner, so A is not recognized as parametric
     class Partner extends AbstractIterator[A] {
       override def knownSize: Int = self.synchronized {
         val thisSize = self.knownSize
@@ -1145,9 +1143,9 @@ object Iterator extends IterableFactory[Iterator] {
    *  Nested ConcatIterators are merged to avoid blowing the stack.
    */
   private final class ConcatIterator[+A](val from: Iterator[A]^) extends AbstractIterator[A] {
-    private var current: Iterator[A @uncheckedCaptures]^{from*} = from
-    private var tail: ConcatIteratorCell[A @uncheckedVariance @uncheckedCaptures] = null
-    private var last: ConcatIteratorCell[A @uncheckedVariance @uncheckedCaptures] = null
+    private var current: Iterator[A]^{from*} = from
+    private var tail: ConcatIteratorCell[A @uncheckedVariance] = null
+    private var last: ConcatIteratorCell[A @uncheckedVariance] = null
     private var currentHasNextChecked = false
 
     def hasNext =
@@ -1216,7 +1214,7 @@ object Iterator extends IterableFactory[Iterator] {
     }
   }
 
-  private[this] final class ConcatIteratorCell[A](head: => IterableOnce[A]^, var tail: ConcatIteratorCell[A @uncheckedCaptures]) {
+  private[this] final class ConcatIteratorCell[A](head: => IterableOnce[A]^, var tail: ConcatIteratorCell[A]) {
     def headIterator: Iterator[A]^{this} = head.iterator // CC todo: can't use {head} as capture set, gives "cannot establish a reference"
   }
 
@@ -1277,8 +1275,8 @@ object Iterator extends IterableFactory[Iterator] {
     * type `A` and update an internal state of type `S`.
     */
   private final class UnfoldIterator[A, S](init: S)(f: S => Option[(A, S)])extends AbstractIterator[A] {
-    private[this] var state: S @uncheckedCaptures = init
-    private[this] var nextResult: Option[(A, S)] @uncheckedCaptures = null
+    private[this] var state: S = init
+    private[this] var nextResult: Option[(A, S)] = null
 
     override def hasNext: Boolean = {
       if (nextResult eq null) {

tests/pos-special/stdlib/collection/Seq.scala

@@ -18,7 +18,6 @@ import Searching.{Found, InsertionPoint, SearchResult}
 import scala.annotation.nowarn
 import language.experimental.captureChecking
 import caps.unsafe.unsafeAssumePure
-import scala.annotation.unchecked.uncheckedCaptures
 
 /** Base trait for sequence collections
   *
@@ -601,8 +600,7 @@ trait SeqOps[+A, +CC[_], +C] extends Any with SeqViewOps[A, CC, C] { self =>
       if (!hasNext)
         Iterator.empty.next()
 
-      val forcedElms = new mutable.ArrayBuffer[A @uncheckedCaptures](elms.size) ++= elms
-        // uncheckedCaptures OK since used only locally
+      val forcedElms = new mutable.ArrayBuffer[A](elms.size) ++= elms
       val result = (newSpecificBuilder ++= forcedElms).result()
       var i = idxs.length - 2
       while(i >= 0 && idxs(i) >= idxs(i+1))
@@ -893,7 +891,7 @@ trait SeqOps[+A, +CC[_], +C] extends Any with SeqViewOps[A, CC, C] { self =>
     *                part of the result, but any following occurrences will.
     */
   def diff[B >: A](that: Seq[B]): C = {
-    val occ = occCounts[B @uncheckedCaptures](that)
+    val occ = occCounts[B](that)
     fromSpecific(iterator.filter { x =>
       var include = false
       occ.updateWith(x) {
@@ -918,7 +916,7 @@ trait SeqOps[+A, +CC[_], +C] extends Any with SeqViewOps[A, CC, C] { self =>
     *                in the result, but any following occurrences will be omitted.
     */
   def intersect[B >: A](that: Seq[B]): C = {
-    val occ = occCounts[B @uncheckedCaptures](that)
+    val occ = occCounts[B](that)
     fromSpecific(iterator.filter { x =>
       var include = true
       occ.updateWith(x) {

tests/pos-special/stdlib/collection/SeqView.scala

@@ -196,7 +196,7 @@ object SeqView {
           //     contains items of another type, we'd get a CCE anyway)
           //   - the cast doesn't actually do anything in the runtime because the
           //     type of A is not known and Array[_] is Array[AnyRef]
-          immutable.ArraySeq.unsafeWrapArray(arr.asInstanceOf[Array[A @uncheckedCaptures]])
+          immutable.ArraySeq.unsafeWrapArray(arr.asInstanceOf[Array[A]])
         }
       }
       evaluated = true

tests/pos-special/stdlib/collection/StrictOptimizedSeqOps.scala

@@ -12,7 +12,6 @@
 
 package scala.collection
 import language.experimental.captureChecking
-import scala.annotation.unchecked.uncheckedCaptures
 
 /**
   * Trait that overrides operations on sequences in order
@@ -25,7 +24,7 @@ trait StrictOptimizedSeqOps [+A, +CC[_], +C]
 
   override def distinctBy[B](f: A -> B): C = {
     val builder = newSpecificBuilder
-    val seen = mutable.HashSet.empty[B @uncheckedCaptures]
+    val seen = mutable.HashSet.empty[B]
     val it = this.iterator
     while (it.hasNext) {
       val next = it.next()
@@ -80,7 +79,7 @@ trait StrictOptimizedSeqOps [+A, +CC[_], +C]
   override def diff[B >: A](that: Seq[B]): C =
     if (isEmpty || that.isEmpty) coll
     else {
-      val occ = occCounts[B @uncheckedCaptures](that)
+      val occ = occCounts[B](that)
       val b = newSpecificBuilder
       for (x <- this) {
         occ.updateWith(x) {
@@ -98,7 +97,7 @@ trait StrictOptimizedSeqOps [+A, +CC[_], +C]
   override def intersect[B >: A](that: Seq[B]): C =
     if (isEmpty || that.isEmpty) empty
     else {
-      val occ = occCounts[B @uncheckedCaptures](that)
+      val occ = occCounts[B](that)
       val b = newSpecificBuilder
       for (x <- this) {
         occ.updateWith(x) {

tests/pos-special/stdlib/collection/View.scala

@@ -15,7 +15,6 @@ package scala.collection
 import scala.annotation.{nowarn, tailrec}
 import scala.collection.mutable.{ArrayBuffer, Builder}
 import scala.collection.immutable.LazyList
-import scala.annotation.unchecked.uncheckedCaptures
 import language.experimental.captureChecking
 
 /** Views are collections whose transformation operations are non strict: the resulting elements
@@ -449,7 +448,7 @@ object View extends IterableFactory[View] {
   }
 
   private final class TakeRightIterator[A](underlying: Iterator[A]^, maxlen: Int) extends AbstractIterator[A] {
-    private[this] var current: Iterator[A @uncheckedCaptures]^{underlying} = underlying
+    private[this] var current: Iterator[A]^{underlying} = underlying
     private[this] var len: Int = -1
     private[this] var pos: Int = 0
     private[this] var buf: ArrayBuffer[AnyRef] = _

tests/pos-special/stdlib/collection/generic/DefaultSerializationProxy.scala

@@ -17,7 +17,6 @@ import java.io.{ObjectInputStream, ObjectOutputStream}
 import scala.collection.{Factory, Iterable}
 import scala.collection.mutable.Builder
 import language.experimental.captureChecking
-import scala.annotation.unchecked.uncheckedCaptures
 
 /** The default serialization proxy for collection implementations.
   *
@@ -29,8 +28,7 @@ import scala.annotation.unchecked.uncheckedCaptures
 @SerialVersionUID(3L)
 final class DefaultSerializationProxy[A](factory: Factory[A, Any], @transient private[this] val coll: Iterable[A]) extends Serializable {
 
-  @transient protected var builder: Builder[A @uncheckedCaptures, Any] = _
-    // @uncheckedCaptures OK since builder is used only locally when reading objects
+  @transient protected var builder: Builder[A, Any] = _
 
   private[this] def writeObject(out: ObjectOutputStream): Unit = {
     out.defaultWriteObject()

tests/pos-special/stdlib/collection/generic/IsSeq.scala

@@ -16,7 +16,6 @@ package generic
 import scala.reflect.ClassTag
 import language.experimental.captureChecking
 import language.experimental.captureChecking
-import scala.annotation.unchecked.uncheckedCaptures
 
 /** Type class witnessing that a collection representation type `Repr` has
   * elements of type `A` and has a conversion to `SeqOps[A, Iterable, C]`, for
@@ -100,7 +99,7 @@ object IsSeq {
         new SeqOps[A, mutable.ArraySeq, Array[A]] {
           def apply(i: Int): A = a(i)
           def length: Int = a.length
-          def toIterable: Iterable[A] = mutable.ArraySeq.make[A @uncheckedCaptures](a)
+          def toIterable: Iterable[A] = mutable.ArraySeq.make[A](a)
           protected def coll: Array[A] = a
           protected def fromSpecific(coll: IterableOnce[A]^): Array[A] = Array.from(coll)
           def iterableFactory: FreeSeqFactory[mutable.ArraySeq] = mutable.ArraySeq.untagged

tests/pos-special/stdlib/collection/immutable/ArraySeq.scala

@@ -24,7 +24,6 @@ import scala.runtime.ScalaRunTime
 import scala.util.Sorting
 import scala.util.hashing.MurmurHash3
 import language.experimental.captureChecking
-import scala.annotation.unchecked.uncheckedCaptures
 
 /**
   * An immutable array.
@@ -59,7 +58,7 @@ sealed abstract class ArraySeq[+A]
   def unsafeArrayAsAnyArray = unsafeArray.asInstanceOf[Array[Any]]
 
   protected def evidenceIterableFactory: ArraySeq.type = ArraySeq
-  protected def iterableEvidence: ClassTag[A @uncheckedVariance @uncheckedCaptures] = elemTag.asInstanceOf[ClassTag[A]]
+  protected def iterableEvidence: ClassTag[A @uncheckedVariance] = elemTag.asInstanceOf[ClassTag[A]]
 
   def stepper[S <: Stepper[_]](implicit shape: StepperShape[A, S]): S with EfficientSplit
 
@@ -109,17 +108,17 @@ sealed abstract class ArraySeq[+A]
         null
       else if (thisIsObj) {
         // A and B are objects
-        val ax = this.unsafeArray.asInstanceOf[Array[A @uncheckedCaptures]]
-        val ay = that.unsafeArray.asInstanceOf[Array[B @uncheckedCaptures]]
+        val ax = this.unsafeArray.asInstanceOf[Array[A]]
+        val ay = that.unsafeArray.asInstanceOf[Array[B]]
         val len = ax.length + ay.length
         val a = new Array[AnyRef](len)
         System.arraycopy(ax, 0, a, 0, ax.length)
         System.arraycopy(ay, 0, a, ax.length, ay.length)
         ArraySeq.unsafeWrapArray(a).asInstanceOf[ArraySeq[B]]
       } else {
         // A is a primative and B = A. Use this instance's protected ClassTag.
-        val ax = this.unsafeArray.asInstanceOf[Array[A @uncheckedCaptures]]
-        val ay = that.unsafeArray.asInstanceOf[Array[A @uncheckedCaptures]]
+        val ax = this.unsafeArray.asInstanceOf[Array[A]]
+        val ay = that.unsafeArray.asInstanceOf[Array[A]]
         val len = ax.length + ay.length
         val a = iterableEvidence.newArray(len)
         System.arraycopy(ax, 0, a, 0, ax.length)
@@ -186,7 +185,7 @@ sealed abstract class ArraySeq[+A]
         strictOptimizedZip[B, ArraySeq[(A, B)]](that, iterableFactory.newBuilder)
     }
 
-  private inline def ops[A](xs: Array[A @uncheckedCaptures]): ArrayOps[A] = new ArrayOps[A @uncheckedCaptures](xs)
+  private inline def ops[A](xs: Array[A]): ArrayOps[A] = new ArrayOps[A](xs)
 
   override def take(n: Int): ArraySeq[A] =
     if (unsafeArray.length <= n)
@@ -290,12 +289,12 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
   }
 
   def newBuilder[A : ClassTag]: Builder[A, ArraySeq[A]] =
-    ArrayBuffer.newBuilder[A @uncheckedCaptures].mapResult(b => unsafeWrapArray[A](b.toArray))
+    ArrayBuffer.newBuilder[A].mapResult(b => unsafeWrapArray[A](b.toArray))
 
   override def fill[A : ClassTag](n: Int)(elem: => A): ArraySeq[A] = tabulate(n)(_ => elem)
 
   override def tabulate[A : ClassTag](n: Int)(f: Int => A): ArraySeq[A] = {
-    val elements = Array.ofDim[A @uncheckedCaptures](scala.math.max(n, 0))
+    val elements = Array.ofDim[A](scala.math.max(n, 0))
     var i = 0
     while (i < n) {
       ScalaRunTime.array_update(elements, i, f(i))
@@ -316,7 +315,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
    * `ArraySeq.unsafeWrapArray(a.asInstanceOf[Array[Int]])` does not work, it throws a
    * `ClassCastException` at runtime.
    */
-  def unsafeWrapArray[T](x: Array[T @uncheckedCaptures]): ArraySeq[T] = ((x: @unchecked) match {
+  def unsafeWrapArray[T](x: Array[T]): ArraySeq[T] = ((x: @unchecked) match {
     case null              => null
     case x: Array[AnyRef]  => new ofRef[AnyRef](x)
     case x: Array[Int]     => new ofInt(x)

tests/pos-special/stdlib/collection/immutable/HashMap.scala

@@ -26,7 +26,6 @@ import scala.runtime.AbstractFunction2
 import scala.runtime.Statics.releaseFence
 import scala.util.hashing.MurmurHash3
 import language.experimental.captureChecking
-import scala.annotation.unchecked.uncheckedCaptures
 
 /** This class implements immutable maps using a Compressed Hash-Array Mapped Prefix-tree.
   * See paper https://michael.steindorfer.name/publications/oopsla15.pdf for more details.
@@ -1768,7 +1767,7 @@ private final class BitmapIndexedMapNode[K, +V](
             } else {
               mapOfNewNodes |= bitpos
               if (newNodes eq null) {
-                newNodes = mutable.Queue.empty[MapNode[K, V] @uncheckedCaptures]
+                newNodes = mutable.Queue.empty[MapNode[K, V]]
               }
               newNodes += newSubNode
             }
@@ -1853,7 +1852,7 @@ private final class BitmapIndexedMapNode[K, +V](
 private final class HashCollisionMapNode[K, +V ](
   val originalHash: Int,
   val hash: Int,
-  var content: Vector[(K, V @uV) @uncheckedCaptures]
+  var content: Vector[(K, V @uV)]
   ) extends MapNode[K, V] {
 
   import Node._
@@ -2157,7 +2156,7 @@ private final class MapKeyValueTupleReverseIterator[K, V](rootNode: MapNode[K, V
 private final class MapKeyValueTupleHashIterator[K, V](rootNode: MapNode[K, V])
   extends ChampBaseReverseIterator[MapNode[K, V]](rootNode) with Iterator[Any] {
   private[this] var hash = 0
-  private[this] var value: V @uncheckedCaptures = _
+  private[this] var value: V = _
   override def hashCode(): Int = MurmurHash3.tuple2Hash(hash, value.##, MurmurHash3.productSeed)
   def next() = {
     if (!hasNext)
@@ -2229,12 +2228,12 @@ private[immutable] final class HashMapBuilder[K, V] extends ReusableBuilder[(K,
   /** The last given out HashMap as a return value of `result()`, if any, otherwise null.
     * Indicates that on next add, the elements should be copied to an identical structure, before continuing
     * mutations. */
-  private var aliased: HashMap[K, V] @uncheckedCaptures = _
+  private var aliased: HashMap[K, V] = _
 
   private def isAliased: Boolean = aliased != null
 
   /** The root node of the partially build hashmap */
-  private var rootNode: BitmapIndexedMapNode[K, V] @uncheckedCaptures = newEmptyRootNode
+  private var rootNode: BitmapIndexedMapNode[K, V] = newEmptyRootNode
 
   private[immutable] def getOrElse[V0 >: V](key: K, value: V0): V0 =
     if (rootNode.size == 0) value