Merge pull request swiftlang#34445 from lorentey/array-cannot-append-5.3

[5.3][stdlib] Fix Array.append(contentsOf:) for arguments of type NSArray

Author: lorentey

stdlib/public/core/Array.swift

@@ -1227,7 +1227,7 @@ extension Array: RangeReplaceableCollection {
       // elements. It reduces code size, because the following code
       // can be removed by the optimizer by constant folding this check in a
       // generic specialization.
-      if newElements is [Element] {
+      if S.self == [Element].self {
         _internalInvariant(remainder.next() == nil)
         return
       }

validation-test/stdlib/ArrayNew.swift.gyb

@@ -1110,6 +1110,15 @@ ArrayTestSuite.test("BridgedToObjC.Nonverbatim.RoundtripThroughSwiftArray") {
   }
 }
 
+ArrayTestSuite.test("append(contentsOf: NSArray)") {
+  // A stray runtime `is` test caused this particular operation to fail in 5.3.
+  // rdar://70448247
+  let nsarray: NSArray = [2, 3, 4]
+  var array: [Any] = [1]
+  array.append(contentsOf: nsarray)
+  expectEqual(array as? [Int], [1, 2, 3, 4])
+}
+
 ArrayTestSuite.setUp {
   resetLeaksOfDictionaryKeysValues()
   resetLeaksOfObjCDictionaryKeysValues()