IArray.toArray: Deprecate broken method, add experimental overload

The cast in the original method is unsound. We can't change this method
to return `Array[? <: T]` without breaking source-compatibility and even
then the resulting method wouldn't be very useful, so deprecate it and
introduces an overload that takes a ClassTag instead. This happens to be
source-compatible because while these overloads are ambiguous, there
exists an implicit conversion from IArray to ArraySeq which also
provides `toArray`.

Author: smarter

library/src/scala/IArray.scala

@@ -1,6 +1,7 @@
 package scala
 import reflect.ClassTag
 
+import scala.annotation.experimental
 import scala.collection.{LazyZip2, SeqView, Searching, Stepper, StepperShape}
 import scala.collection.immutable.ArraySeq
 import scala.collection.mutable.{ArrayBuilder, Builder}
@@ -249,9 +250,18 @@ object IArray:
   extension [T](arr: IArray[T]) def takeWhile(p: T => Boolean): IArray[T] =
     genericArrayOps(arr).takeWhile(p)
 
-  /** Returns a mutable copy of this immutable array. */
-  extension [T](arr: IArray[T]) def toArray: Array[T] =
-    arr.clone.asInstanceOf[Array[T]]
+  // NOTE: these two overloads are never selected when calling toArray on an
+  // IArray because they're considered ambiguous, but such calls still typecheck
+  // because of the implicit conversion `genericWrapArray`.
+  extension [T](arr: IArray[T])
+    /** Returns a mutable copy of this immutable array. */
+    @deprecated("This method implementation is incorrect and calling it can crash your program, please use the other overload.", "3.0.1")
+    def toArray: Array[T] =
+      arr.clone.asInstanceOf[Array[T]]
+    /** Returns a mutable copy of this immutable array. */
+    @experimental
+    def toArray[U >: T: ClassTag]: Array[U] =
+      Array.copyAs(arr, arr.length)
 
   extension [T](arr: IArray[T])
     def ++[U >: T: ClassTag](suffix: IArray[U]): IArray[U] = genericArrayOps(arr) ++ suffix.toSeq

project/MiMaFilters.scala

@@ -15,6 +15,7 @@ object MiMaFilters {
     exclude[DirectMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SymbolMethods.typeMembers"),
     exclude[DirectMissingMethodProblem]("scala.quoted.Quotes#reflectModule#TermParamClauseMethods.isErased"),
     exclude[DirectMissingMethodProblem]("scala.quoted.Type.valueOfTuple"),
+    exclude[DirectMissingMethodProblem]("scala.IArray#package#IArray.toArray"),
     exclude[MissingClassProblem]("scala.annotation.experimental"),
     exclude[MissingClassProblem]("scala.annotation.internal.ErasedParam"),
     exclude[MissingClassProblem]("scala.annotation.internal.ErasedParam"),

tests/run/i12597.scala

@@ -0,0 +1,5 @@
+@main def Test =
+  val a: IArray[Int] = IArray(2)
+  val b: IArray[Any] = a
+  val c = b.toArray
+  c(0) = ""