Add explicit result type to some non-private methods

Add explicit result type to methods where Scala 2 and Scala 3 disagree
with the inferred type. The aim is to have the same type in the Scala 2
pickles and the Scala 3 TASTy.

Follow up of scala/scala#10435

These where identified in and tested in
  * #18032
  * #18029
  * #17975 (BitSet)

Author: nicolasstucki

library/src/scala/collection/concurrent/TrieMap.scala

@@ -438,7 +438,7 @@ private[concurrent] object INode {
 private[concurrent] final class FailedNode[K, V](p: MainNode[K, V]) extends MainNode[K, V] {
   WRITE_PREV(p)
 
-  def string(lev: Int) = throw new UnsupportedOperationException
+  def string(lev: Int): Nothing = throw new UnsupportedOperationException
 
   def cachedSize(ct: AnyRef): Int = throw new UnsupportedOperationException
 

library/src/scala/collection/immutable/ArraySeq.scala

@@ -325,7 +325,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofRef[T <: AnyRef](val unsafeArray: Array[T]) extends ArraySeq[T] {
-    def elemTag = ClassTag[T](unsafeArray.getClass.getComponentType)
+    def elemTag: ClassTag[T] = ClassTag[T](unsafeArray.getClass.getComponentType)
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): T = unsafeArray(i)

library/src/scala/collection/immutable/BitSet.scala

@@ -41,7 +41,7 @@ sealed abstract class BitSet
   override protected def newSpecificBuilder: Builder[Int, BitSet] = bitSetFactory.newBuilder
   override def empty: BitSet = bitSetFactory.empty
 
-  def bitSetFactory = BitSet
+  def bitSetFactory: BitSet.type = BitSet
 
   protected[collection] def fromBitMaskNoCopy(elems: Array[Long]): BitSet = BitSet.fromBitMaskNoCopy(elems)
 

library/src/scala/collection/mutable/ArraySeq.scala

@@ -139,7 +139,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofRef[T <: AnyRef](val array: Array[T]) extends ArraySeq[T] {
-    def elemTag = ClassTag[T](array.getClass.getComponentType)
+    def elemTag: ClassTag[T] = ClassTag[T](array.getClass.getComponentType)
     def length: Int = array.length
     def apply(index: Int): T = array(index)
     def update(index: Int, elem: T): Unit = { array(index) = elem }
@@ -161,7 +161,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofByte(val array: Array[Byte]) extends ArraySeq[Byte] {
-    def elemTag = ClassTag.Byte
+    def elemTag: ClassTag.Byte.type = ClassTag.Byte
     def length: Int = array.length
     def apply(index: Int): Byte = array(index)
     def update(index: Int, elem: Byte): Unit = { array(index) = elem }
@@ -180,7 +180,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofShort(val array: Array[Short]) extends ArraySeq[Short] {
-    def elemTag = ClassTag.Short
+    def elemTag: ClassTag.Short.type = ClassTag.Short
     def length: Int = array.length
     def apply(index: Int): Short = array(index)
     def update(index: Int, elem: Short): Unit = { array(index) = elem }
@@ -199,7 +199,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofChar(val array: Array[Char]) extends ArraySeq[Char] {
-    def elemTag = ClassTag.Char
+    def elemTag: ClassTag.Char.type = ClassTag.Char
     def length: Int = array.length
     def apply(index: Int): Char = array(index)
     def update(index: Int, elem: Char): Unit = { array(index) = elem }
@@ -239,7 +239,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofInt(val array: Array[Int]) extends ArraySeq[Int] {
-    def elemTag = ClassTag.Int
+    def elemTag: ClassTag.Int.type = ClassTag.Int
     def length: Int = array.length
     def apply(index: Int): Int = array(index)
     def update(index: Int, elem: Int): Unit = { array(index) = elem }
@@ -258,7 +258,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofLong(val array: Array[Long]) extends ArraySeq[Long] {
-    def elemTag = ClassTag.Long
+    def elemTag: ClassTag.Long.type = ClassTag.Long
     def length: Int = array.length
     def apply(index: Int): Long = array(index)
     def update(index: Int, elem: Long): Unit = { array(index) = elem }
@@ -277,7 +277,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofFloat(val array: Array[Float]) extends ArraySeq[Float] {
-    def elemTag = ClassTag.Float
+    def elemTag: ClassTag.Float.type = ClassTag.Float
     def length: Int = array.length
     def apply(index: Int): Float = array(index)
     def update(index: Int, elem: Float): Unit = { array(index) = elem }
@@ -296,7 +296,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofDouble(val array: Array[Double]) extends ArraySeq[Double] {
-    def elemTag = ClassTag.Double
+    def elemTag: ClassTag.Double.type = ClassTag.Double
     def length: Int = array.length
     def apply(index: Int): Double = array(index)
     def update(index: Int, elem: Double): Unit = { array(index) = elem }
@@ -315,7 +315,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofBoolean(val array: Array[Boolean]) extends ArraySeq[Boolean] {
-    def elemTag = ClassTag.Boolean
+    def elemTag: ClassTag.Boolean.type = ClassTag.Boolean
     def length: Int = array.length
     def apply(index: Int): Boolean = array(index)
     def update(index: Int, elem: Boolean): Unit = { array(index) = elem }
@@ -331,7 +331,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
 
   @SerialVersionUID(3L)
   final class ofUnit(val array: Array[Unit]) extends ArraySeq[Unit] {
-    def elemTag = ClassTag.Unit
+    def elemTag: ClassTag.Unit.type = ClassTag.Unit
     def length: Int = array.length
     def apply(index: Int): Unit = array(index)
     def update(index: Int, elem: Unit): Unit = { array(index) = elem }

library/src/scala/collection/mutable/BitSet.scala

@@ -51,7 +51,7 @@ class BitSet(protected[collection] final var elems: Array[Long])
   override protected def newSpecificBuilder: Builder[Int, BitSet] = bitSetFactory.newBuilder
   override def empty: BitSet = bitSetFactory.empty
 
-  def bitSetFactory = BitSet
+  def bitSetFactory: BitSet.type = BitSet
 
   override def unsorted: Set[Int] = this
 

library/src/scala/collection/mutable/UnrolledBuffer.scala

@@ -89,7 +89,7 @@ sealed class UnrolledBuffer[T](implicit val tag: ClassTag[T])
   // def setLengthPolicy(nextLength: Int => Int): Unit = { myLengthPolicy = nextLength }
   private[collection] def calcNextLength(sz: Int) = sz // myLengthPolicy(sz)
 
-  def classTagCompanion = UnrolledBuffer
+  def classTagCompanion: UnrolledBuffer.type = UnrolledBuffer
 
   /** Concatenates the target unrolled buffer to this unrolled buffer.
     *

library/src/scala/reflect/Manifest.scala

@@ -173,7 +173,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class ByteManifest extends AnyValManifest[scala.Byte]("Byte") {
-    def runtimeClass = java.lang.Byte.TYPE
+    def runtimeClass: Class[java.lang.Byte] = java.lang.Byte.TYPE
     @inline override def newArray(len: Int): Array[Byte] = new Array[Byte](len)
     override def newWrappedArray(len: Int): ArraySeq[Byte] = new ArraySeq.ofByte(new Array[Byte](len))
     override def newArrayBuilder(): ArrayBuilder[Byte] = new ArrayBuilder.ofByte()
@@ -189,7 +189,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class ShortManifest extends AnyValManifest[scala.Short]("Short") {
-    def runtimeClass = java.lang.Short.TYPE
+    def runtimeClass: Class[java.lang.Short] = java.lang.Short.TYPE
     @inline override def newArray(len: Int): Array[Short] = new Array[Short](len)
     override def newWrappedArray(len: Int): ArraySeq[Short] = new ArraySeq.ofShort(new Array[Short](len))
     override def newArrayBuilder(): ArrayBuilder[Short] = new ArrayBuilder.ofShort()
@@ -205,7 +205,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class CharManifest extends AnyValManifest[scala.Char]("Char") {
-    def runtimeClass = java.lang.Character.TYPE
+    def runtimeClass: Class[java.lang.Character] = java.lang.Character.TYPE
     @inline override def newArray(len: Int): Array[Char] = new Array[Char](len)
     override def newWrappedArray(len: Int): ArraySeq[Char] = new ArraySeq.ofChar(new Array[Char](len))
     override def newArrayBuilder(): ArrayBuilder[Char] = new ArrayBuilder.ofChar()
@@ -221,7 +221,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class IntManifest extends AnyValManifest[scala.Int]("Int") {
-    def runtimeClass = java.lang.Integer.TYPE
+    def runtimeClass: Class[java.lang.Integer] = java.lang.Integer.TYPE
     @inline override def newArray(len: Int): Array[Int] = new Array[Int](len)
     override def newWrappedArray(len: Int): ArraySeq[Int] = new ArraySeq.ofInt(new Array[Int](len))
     override def newArrayBuilder(): ArrayBuilder[Int] = new ArrayBuilder.ofInt()
@@ -237,7 +237,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class LongManifest extends AnyValManifest[scala.Long]("Long") {
-    def runtimeClass = java.lang.Long.TYPE
+    def runtimeClass: Class[java.lang.Long] = java.lang.Long.TYPE
     @inline override def newArray(len: Int): Array[Long] = new Array[Long](len)
     override def newWrappedArray(len: Int): ArraySeq[Long] = new ArraySeq.ofLong(new Array[Long](len))
     override def newArrayBuilder(): ArrayBuilder[Long] = new ArrayBuilder.ofLong()
@@ -253,7 +253,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class FloatManifest extends AnyValManifest[scala.Float]("Float") {
-    def runtimeClass = java.lang.Float.TYPE
+    def runtimeClass: Class[java.lang.Float] = java.lang.Float.TYPE
     @inline override def newArray(len: Int): Array[Float] = new Array[Float](len)
     override def newWrappedArray(len: Int): ArraySeq[Float] = new ArraySeq.ofFloat(new Array[Float](len))
     override def newArrayBuilder(): ArrayBuilder[Float] = new ArrayBuilder.ofFloat()
@@ -269,7 +269,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class DoubleManifest extends AnyValManifest[scala.Double]("Double") {
-    def runtimeClass = java.lang.Double.TYPE
+    def runtimeClass: Class[java.lang.Double] = java.lang.Double.TYPE
     @inline override def newArray(len: Int): Array[Double] = new Array[Double](len)
     override def newWrappedArray(len: Int): ArraySeq[Double] = new ArraySeq.ofDouble(new Array[Double](len))
     override def newArrayBuilder(): ArrayBuilder[Double] = new ArrayBuilder.ofDouble()
@@ -286,7 +286,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class BooleanManifest extends AnyValManifest[scala.Boolean]("Boolean") {
-    def runtimeClass = java.lang.Boolean.TYPE
+    def runtimeClass: Class[java.lang.Boolean] = java.lang.Boolean.TYPE
     @inline override def newArray(len: Int): Array[Boolean] = new Array[Boolean](len)
     override def newWrappedArray(len: Int): ArraySeq[Boolean] = new ArraySeq.ofBoolean(new Array[Boolean](len))
     override def newArrayBuilder(): ArrayBuilder[Boolean] = new ArrayBuilder.ofBoolean()
@@ -302,7 +302,7 @@ object ManifestFactory {
 
   @SerialVersionUID(1L)
   final private[reflect] class UnitManifest extends AnyValManifest[scala.Unit]("Unit") {
-    def runtimeClass = java.lang.Void.TYPE
+    def runtimeClass: Class[java.lang.Void] = java.lang.Void.TYPE
     @inline override def newArray(len: Int): Array[Unit] = new Array[Unit](len)
     override def newWrappedArray(len: Int): ArraySeq[Unit] = new ArraySeq.ofUnit(new Array[Unit](len))
     override def newArrayBuilder(): ArrayBuilder[Unit] = new ArrayBuilder.ofUnit()