From 4cfb637932e6f9e02adacf24d058b4574d654d12 Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Tue, 25 May 2021 16:00:51 +0200
Subject: [PATCH] IArray.toArray: Deprecate broken method

The cast in the original method is unsound. Any attempt at fixing
this would break source-compatibility, so this commit only deprecates
it, to be revisited for 3.1.
---
 library/src/scala/IArray.scala                 | 8 +++++---
 tests/neg-custom-args/deprecation/i12597.scala | 5 +++++
 tests/run/i12597.scala                         | 5 +++++
 3 files changed, 15 insertions(+), 3 deletions(-)
 create mode 100644 tests/neg-custom-args/deprecation/i12597.scala
 create mode 100644 tests/run/i12597.scala

diff --git a/library/src/scala/IArray.scala b/library/src/scala/IArray.scala
index 50d40b6f2f19..c5679ae7aaf9 100644
--- a/library/src/scala/IArray.scala
+++ b/library/src/scala/IArray.scala
@@ -249,9 +249,11 @@ 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]]
+  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 `IArray.genericWrapArray(myIArray).toArray` instead.", "3.0.1")
+    def toArray: Array[T] =
+      arr.clone.asInstanceOf[Array[T]]
 
   extension [T](arr: IArray[T])
     def ++[U >: T: ClassTag](suffix: IArray[U]): IArray[U] = genericArrayOps(arr) ++ suffix.toSeq
diff --git a/tests/neg-custom-args/deprecation/i12597.scala b/tests/neg-custom-args/deprecation/i12597.scala
new file mode 100644
index 000000000000..7927dded0cbc
--- /dev/null
+++ b/tests/neg-custom-args/deprecation/i12597.scala
@@ -0,0 +1,5 @@
+@main def Test =
+  val a: IArray[Int] = IArray(2)
+  val b: IArray[Any] = a
+  val c = b.toArray // error: deprecated
+  c(0) = ""
diff --git a/tests/run/i12597.scala b/tests/run/i12597.scala
new file mode 100644
index 000000000000..73cc4185d74e
--- /dev/null
+++ b/tests/run/i12597.scala
@@ -0,0 +1,5 @@
+@main def Test =
+  val a: IArray[Int] = IArray(2)
+  val b: IArray[Any] = a
+  val c = IArray.genericWrapArray(b).toArray
+  c(0) = ""