Explicitly null check the stdlib

library/src/scala/Enumeration.scala

@@ -107,7 +107,7 @@ abstract class Enumeration (initial: Int) extends Serializable {
   private val vmap: mutable.Map[Int, Value] = new mutable.HashMap
 
   /** The cache listing all values of this enumeration. */
-  @transient private var vset: ValueSet = null
+  @transient @annotation.stableNull private var vset: ValueSet | Null = null
   @transient @volatile private var vsetDefined = false
 
   /** The mapping from the integer used to identify values to their
@@ -121,7 +121,7 @@ abstract class Enumeration (initial: Int) extends Serializable {
       vset = (ValueSet.newBuilder ++= vmap.values).result()
       vsetDefined = true
     }
-    vset
+    vset.nn
   }
 
   /** The integer to use to identify the next created value. */
@@ -130,7 +130,7 @@ abstract class Enumeration (initial: Int) extends Serializable {
   /** The string to use to name the next created value. */
   protected var nextName: Iterator[String] = _
 
-  private def nextNameOrNull =
+  private def nextNameOrNull: String | Null =
     if (nextName != null && nextName.hasNext) nextName.next() else null
 
   /** The highest integer amongst those used to identify values in this
@@ -177,7 +177,7 @@ abstract class Enumeration (initial: Int) extends Serializable {
    *  @param name A human-readable name for that value.
    *  @return  Fresh value called `name`.
    */
-  protected final def Value(name: String): Value = Value(nextId, name)
+  protected final def Value(name: String | Null): Value = Value(nextId, name)
 
   /** Creates a fresh value, part of this enumeration, called `name`
    *  and identified by the integer `i`.
@@ -187,7 +187,7 @@ abstract class Enumeration (initial: Int) extends Serializable {
    * @param name A human-readable name for that value.
    * @return     Fresh value with the provided identifier `i` and name `name`.
    */
-  protected final def Value(i: Int, name: String): Value = new Val(i, name)
+  protected final def Value(i: Int, name: String | Null): Value = new Val(i, name)
 
   private def populateNameMap(): Unit = {
     @tailrec def getFields(clazz: Class[_], acc: Array[JField]): Array[JField] = {
@@ -248,7 +248,7 @@ abstract class Enumeration (initial: Int) extends Serializable {
    *  identification behaviour.
    */
   @SerialVersionUID(0 - 3501153230598116017L)
-  protected class Val(i: Int, name: String) extends Value with Serializable {
+  protected class Val(i: Int, name: String | Null) extends Value with Serializable {
     def this(i: Int)       = this(i, nextNameOrNull)
     def this(name: String) = this(nextId, name)
     def this()             = this(nextId)

library/src/scala/Predef.scala

@@ -122,7 +122,7 @@ object Predef extends LowPriorityImplicits {
    * @return The runtime [[Class]] representation of type `T`.
    * @group utilities
    */
-  def classOf[T]: Class[T] = null // This is a stub method. The actual implementation is filled in by the compiler.
+  def classOf[T]: Class[T] = null.asInstanceOf[Class[T]] // This is a stub method. The actual implementation is filled in by the compiler.
 
   /**
    * Retrieve the single value of a type with a unique inhabitant.
@@ -286,12 +286,12 @@ object Predef extends LowPriorityImplicits {
      to be available at runtime.
      To achieve this, we keep the Scala 3 signature publicly available.
      We rely on the fact that it is `inline` and will not be visible in the bytecode.
-     To add the required Scala 2 ones, we define the `scala2Assert`, we use: 
-      - `@targetName` to swap the name in the generated code to `assert` 
+     To add the required Scala 2 ones, we define the `scala2Assert`, we use:
+      - `@targetName` to swap the name in the generated code to `assert`
       - `@publicInBinary` to make it available during runtime.
      As such, we would successfully hijack the definitions of `assert` such as:
       - At compile time, we would have the definitions of `assert`
-      - At runtime, the definitions of `scala2Assert` as `assert`  
+      - At runtime, the definitions of `scala2Assert` as `assert`
     NOTE: Tasty-Reader in Scala 2 will have to learn about this swapping if we are to
     allow loading the full Scala 3 library by it.
     */
@@ -426,7 +426,7 @@ object Predef extends LowPriorityImplicits {
     @inline def formatted(fmtstr: String): String = fmtstr format self
   }
 
-  /** Injects String concatenation operator `+` to any classes. 
+  /** Injects String concatenation operator `+` to any classes.
    * @group implicit-classes-any
    */
   @(deprecated @companionMethod)("Implicit injection of + is deprecated. Convert to String to call +", "2.13.0")
@@ -658,46 +658,46 @@ private[scala] abstract class LowPriorityImplicits extends LowPriorityImplicits2
   @inline implicit def booleanWrapper(x: Boolean): runtime.RichBoolean = new runtime.RichBoolean(x)
 
   /** @group conversions-array-to-wrapped-array */
-  implicit def genericWrapArray[T](xs: Array[T]): ArraySeq[T] =
+  implicit def genericWrapArray[T](xs: Array[T] | Null): ArraySeq[T] | Null =
     if (xs eq null) null
     else ArraySeq.make(xs)
 
   // Since the JVM thinks arrays are covariant, one 0-length Array[AnyRef]
   // is as good as another for all T <: AnyRef.  Instead of creating 100,000,000
   // unique ones by way of this implicit, let's share one.
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapRefArray[T <: AnyRef](xs: Array[T]): ArraySeq.ofRef[T] = {
+  implicit def wrapRefArray[T <: AnyRef](xs: Array[T] | Null): ArraySeq.ofRef[T] | Null = {
     if (xs eq null) null
     else if (xs.length == 0) ArraySeq.empty[AnyRef].asInstanceOf[ArraySeq.ofRef[T]]
     else new ArraySeq.ofRef[T](xs)
   }
 
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapIntArray(xs: Array[Int]): ArraySeq.ofInt = if (xs ne null) new ArraySeq.ofInt(xs) else null
+  implicit def wrapIntArray(xs: Array[Int] | Null): ArraySeq.ofInt | Null = if (xs ne null) new ArraySeq.ofInt(xs) else null
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapDoubleArray(xs: Array[Double]): ArraySeq.ofDouble = if (xs ne null) new ArraySeq.ofDouble(xs) else null
+  implicit def wrapDoubleArray(xs: Array[Double] | Null): ArraySeq.ofDouble | Null = if (xs ne null) new ArraySeq.ofDouble(xs) else null
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapLongArray(xs: Array[Long]): ArraySeq.ofLong = if (xs ne null) new ArraySeq.ofLong(xs) else null
+  implicit def wrapLongArray(xs: Array[Long] | Null): ArraySeq.ofLong | Null = if (xs ne null) new ArraySeq.ofLong(xs) else null
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapFloatArray(xs: Array[Float]): ArraySeq.ofFloat = if (xs ne null) new ArraySeq.ofFloat(xs) else null
+  implicit def wrapFloatArray(xs: Array[Float] | Null): ArraySeq.ofFloat | Null = if (xs ne null) new ArraySeq.ofFloat(xs) else null
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapCharArray(xs: Array[Char]): ArraySeq.ofChar = if (xs ne null) new ArraySeq.ofChar(xs) else null
+  implicit def wrapCharArray(xs: Array[Char] | Null): ArraySeq.ofChar | Null = if (xs ne null) new ArraySeq.ofChar(xs) else null
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapByteArray(xs: Array[Byte]): ArraySeq.ofByte = if (xs ne null) new ArraySeq.ofByte(xs) else null
+  implicit def wrapByteArray(xs: Array[Byte] | Null): ArraySeq.ofByte | Null = if (xs ne null) new ArraySeq.ofByte(xs) else null
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapShortArray(xs: Array[Short]): ArraySeq.ofShort = if (xs ne null) new ArraySeq.ofShort(xs) else null
+  implicit def wrapShortArray(xs: Array[Short] | Null): ArraySeq.ofShort | Null = if (xs ne null) new ArraySeq.ofShort(xs) else null
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapBooleanArray(xs: Array[Boolean]): ArraySeq.ofBoolean = if (xs ne null) new ArraySeq.ofBoolean(xs) else null
+  implicit def wrapBooleanArray(xs: Array[Boolean] | Null): ArraySeq.ofBoolean | Null = if (xs ne null) new ArraySeq.ofBoolean(xs) else null
   /** @group conversions-array-to-wrapped-array */
-  implicit def wrapUnitArray(xs: Array[Unit]): ArraySeq.ofUnit = if (xs ne null) new ArraySeq.ofUnit(xs) else null
+  implicit def wrapUnitArray(xs: Array[Unit] | Null): ArraySeq.ofUnit | Null = if (xs ne null) new ArraySeq.ofUnit(xs) else null
 
   /** @group conversions-string */
-  implicit def wrapString(s: String): WrappedString = if (s ne null) new WrappedString(s) else null
+  implicit def wrapString(s: String | Null): WrappedString | Null = if (s ne null) new WrappedString(s) else null
 }
 
 private[scala] abstract class LowPriorityImplicits2 {
   @deprecated("implicit conversions from Array to immutable.IndexedSeq are implemented by copying; use `toIndexedSeq` explicitly if you want to copy, or use the more efficient non-copying ArraySeq.unsafeWrapArray", since="2.13.0")
-  implicit def copyArrayToImmutableIndexedSeq[T](xs: Array[T]): IndexedSeq[T] =
+  implicit def copyArrayToImmutableIndexedSeq[T](xs: Array[T] | Null): IndexedSeq[T] | Null =
     if (xs eq null) null
     else new ArrayOps(xs).toIndexedSeq
 }

library/src/scala/Specializable.scala

@@ -24,17 +24,17 @@ object Specializable {
   trait SpecializedGroup
 
   // Smuggle a list of types by way of a tuple upon which Group is parameterized.
-  class Group[T >: Null](value: T) extends SpecializedGroup
+  class Group[T](value: T) extends SpecializedGroup
 
-  final val Primitives:  Group[(Byte, Short, Int, Long, Char, Float, Double, Boolean, Unit)] = null
-  final val Everything:  Group[(Byte, Short, Int, Long, Char, Float, Double, Boolean, Unit, AnyRef)] = null
-  final val Bits32AndUp: Group[(Int, Long, Float, Double)] = null
-  final val Integral:    Group[(Byte, Short, Int, Long, Char)] = null
-  final val AllNumeric:  Group[(Byte, Short, Int, Long, Char, Float, Double)] = null
-  final val BestOfBreed: Group[(Int, Double, Boolean, Unit, AnyRef)] = null
-  final val Unit:        Group[Tuple1[Unit]] = null
+  final val Primitives:  Group[(Byte, Short, Int, Long, Char, Float, Double, Boolean, Unit)] = null.asInstanceOf
+  final val Everything:  Group[(Byte, Short, Int, Long, Char, Float, Double, Boolean, Unit, AnyRef)] = null.asInstanceOf
+  final val Bits32AndUp: Group[(Int, Long, Float, Double)] = null.asInstanceOf
+  final val Integral:    Group[(Byte, Short, Int, Long, Char)] = null.asInstanceOf
+  final val AllNumeric:  Group[(Byte, Short, Int, Long, Char, Float, Double)] = null.asInstanceOf
+  final val BestOfBreed: Group[(Int, Double, Boolean, Unit, AnyRef)] = null.asInstanceOf
+  final val Unit:        Group[Tuple1[Unit]] = null.asInstanceOf
 
-  final val Arg:         Group[(Int, Long, Float, Double)] = null
-  final val Args:        Group[(Int, Long, Double)] = null
-  final val Return:      Group[(Int, Long, Float, Double, Boolean, Unit)] = null
+  final val Arg:         Group[(Int, Long, Float, Double)] = null.asInstanceOf
+  final val Args:        Group[(Int, Long, Double)] = null.asInstanceOf
+  final val Return:      Group[(Int, Long, Float, Double, Boolean, Unit)] = null.asInstanceOf
 }