[tests] Fix cast_test and migrate to nnbd.

Also splits up cast_test to test collections separately and
updates corelib_2 version with the same changes, including
fixes in relevant pending CL:
https://dart-review.googlesource.com/c/sdk/+/126320

Fixes #39517

Bug: http://dartbug.com/39517
Change-Id: I8df1fde1d48ed23561ce9d0d8b87d7fc2ba52eb1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/144469
Commit-Queue: Riley Porter <rileyporter@google.com>
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>

tests/corelib/cast_errors_test.dart

@@ -0,0 +1,36 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import 'cast_helper.dart';
+
+void main() {
+  testSetDowncast();
+  testMapDowncast();
+}
+
+void testSetDowncast() {
+  var setEls = new Set<C?>.from(elements);
+  var dSet = Set.castFrom<C?, D?>(setEls);
+
+  var newC = new C();
+  dSet.add(newC);
+  //       ^^^^
+  // [analyzer] STATIC_WARNING.ARGUMENT_TYPE_NOT_ASSIGNABLE
+  // [cfe] The argument type 'C' can't be assigned to the parameter type 'D?'.
+}
+
+void testMapDowncast() {
+  var map = new Map.fromIterables(elements, elements);
+  var dMap = Map.castFrom<C?, C?, D?, D?>(map);
+
+  dMap[c] = d;
+  //   ^
+  // [analyzer] STATIC_WARNING.ARGUMENT_TYPE_NOT_ASSIGNABLE
+  // [cfe] A value of type 'C' can't be assigned to a variable of type 'D?'.
+  dMap[d] = c;
+  //        ^
+  // [analyzer] STATIC_TYPE_WARNING.INVALID_ASSIGNMENT
+  // [cfe] A value of type 'C' can't be assigned to a variable of type 'D?'.
+}

tests/corelib/cast_helper.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+final elements = <C?>[c, d, e, f, null];
+
+class C {}
+
+class D extends C {}
+
+class E extends C {}
+
+class F implements D, E {}
+
+final c = C();
+final d = D();
+final e = E();
+final f = F();

tests/corelib/cast_iterable_test.dart

@@ -0,0 +1,68 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testDowncastDirectAccess();
+  testDowncastNoDirectAccess();
+  testDowncastUntouchableElements();
+  testUpcast();
+}
+
+void testDowncastDirectAccess() {
+  var iterable = new Iterable<C?>.generate(elements.length, (n) => elements[n]);
+
+  // An iterable that (likely) can do direct access.
+  var dIterable = Iterable.castFrom<C?, D?>(iterable);
+
+  Expect.throws(() => dIterable.first);
+  Expect.equals(d, dIterable.elementAt(1));
+  Expect.throws(() => dIterable.elementAt(2)); // E is not D?
+  Expect.equals(f, dIterable.skip(3).first); // Skip does not access element.
+  Expect.equals(null, dIterable.skip(3).elementAt(1));
+
+  Expect.throws(() => dIterable.toList());
+}
+
+void testDowncastNoDirectAccess() {
+  var iterable = new Iterable<C?>.generate(elements.length, (n) => elements[n]);
+
+  // An iterable that cannot do direct access.
+  var dIterable = Iterable.castFrom<C?, D?>(iterable.where((_) => true));
+
+  Expect.throws(() => dIterable.first);
+  Expect.equals(d, dIterable.elementAt(1));
+  // E is not D?.
+  Expect.throws(() => dIterable.elementAt(2));
+  Expect.equals(f, dIterable.skip(3).first); // Skip does not access element.
+  Expect.equals(null, dIterable.skip(3).elementAt(1));
+
+  Expect.throws(() => dIterable.toList());
+}
+
+void testDowncastUntouchableElements() {
+  // Iterable that definitely won't survive accessing element 3.
+  var iterable = new Iterable<C?>.generate(
+      elements.length, (n) => n == 3 ? throw "untouchable" : elements[n]);
+  var dIterable = Iterable.castFrom<C?, D?>(iterable);
+
+  Expect.throws(() => dIterable.first);
+  Expect.equals(d, dIterable.elementAt(1));
+  Expect.throws(() => dIterable.elementAt(3));
+  // Skip does not access element.
+  Expect.equals(null, dIterable.skip(4).first);
+  Expect.equals(null, dIterable.skip(3).elementAt(1));
+
+  Expect.throws(() => dIterable.toList());
+}
+
+void testUpcast() {
+  var iterable = new Iterable<C?>.generate(elements.length, (n) => elements[n]);
+
+  var objectIterable = Iterable.castFrom<C?, Object?>(iterable);
+  Expect.listEquals(elements, objectIterable.toList());
+}

tests/corelib/cast_list_test.dart

@@ -0,0 +1,46 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testDowncast();
+  testUpcast();
+  testRegression();
+}
+
+void testDowncast() {
+  var list = new List<C?>.from(elements);
+  var dList = List.castFrom<C?, D?>(list);
+
+  Expect.throws(() => dList.first); // C is not D?.
+  Expect.equals(d, dList[1]);
+  Expect.throws(() => dList[2]); // E is not D?.
+  Expect.equals(f, dList[3]);
+  Expect.equals(null, dList.last);
+
+  Expect.throws(() => dList.toList());
+
+  // Setting works.
+  dList[2] = d;
+  Expect.equals(d, dList[2]);
+}
+
+void testUpcast() {
+  var list = new List<C?>.from(elements);
+  var objectList = List.castFrom<C?, Object?>(list);
+  Expect.listEquals(elements, objectList);
+  Expect.throws(() => objectList[2] = new Object()); // Cannot set non-C.
+  Expect.listEquals(elements, objectList);
+}
+
+void testRegression() {
+  var numList = <num>[4, 3, 2, 1];
+  var intList = numList.cast<int>();
+  intList.sort(null);
+  Expect.listEquals([1, 2, 3, 4], numList);
+  Expect.listEquals([1, 2, 3, 4], intList);
+}

tests/corelib/cast_map_test.dart

@@ -0,0 +1,57 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testDowncast();
+  testUpcast();
+}
+
+void testDowncast() {
+  var map = new Map.fromIterables(elements, elements);
+  var dMap = Map.castFrom<C?, C?, D?, D?>(map);
+
+  Expect.isTrue(dMap is Map<D?, D?>);
+
+  Expect.equals(null, dMap[new C()]);
+  Expect.throws(() => dMap[c]); // C is not D?.
+  Expect.isTrue(dMap.containsKey(c)); // containsKey should not be typed.
+  Expect.equals(d, dMap[d]);
+  Expect.throws(() => dMap[e]); // E is not D?.
+  Expect.isTrue(dMap.containsKey(null));
+  Expect.equals(null, dMap[null]);
+
+  Expect.equals(5, dMap.length);
+  Expect.throws(() => dMap.remove(c)); // Removes key but fails to return value.
+  Expect.equals(4, dMap.length);
+  Expect.equals(null, dMap[c]);
+
+  // Test keys and values.
+  Expect.isTrue(dMap.keys is Iterable<D?>);
+  Expect.isTrue(dMap.values is Iterable<D?>);
+  Expect.throws(() => dMap.keys.toList());
+  Expect.throws(() => dMap.values.toList());
+}
+
+void testUpcast() {
+  var map = new Map.fromIterables(elements, elements);
+  var objectMap = Map.castFrom<C?, C?, Object?, Object?>(map);
+
+  Expect.equals(5, objectMap.length);
+  Expect.equals(c, objectMap[c]);
+  Expect.isTrue(objectMap.containsKey(c));
+  Expect.equals(c, objectMap.remove(c));
+  Expect.equals(4, objectMap.length);
+
+  // Test keys and values.
+  Expect.isTrue(objectMap.keys is Iterable<Object?>);
+  Expect.isTrue(objectMap.values is Iterable<Object?>);
+  var expected = new List<Object?>.from(elements);
+  expected.remove(c);
+  Expect.listEquals(expected, objectMap.keys.toList());
+  Expect.listEquals(expected, objectMap.values.toList());
+}

tests/corelib/cast_set_test.dart

@@ -0,0 +1,71 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testOrder();
+  testDowncast();
+  testUpcast();
+  testNewSet();
+}
+
+void testOrder() {
+  var setEls = new Set<C?>.from(elements); // Linked HashSet.
+  Expect.listEquals(elements, setEls.toList()); // Preserves order.
+}
+
+void testDowncast() {
+  var setEls = new Set<C?>.from(elements);
+  var dSet = Set.castFrom<C?, D?>(setEls);
+
+  // Preserves order.
+  Expect.throws(() => dSet.first); // C is not D?.
+  Expect.equals(d, dSet.elementAt(1));
+  Expect.throws(() => dSet.elementAt(2)); // E is not D?.
+  Expect.equals(f, dSet.elementAt(3));
+  Expect.equals(null, dSet.elementAt(4));
+
+  Expect.throws(() => dSet.toList());
+
+  // Contains should not be typed.
+  var newC = new C();
+  Expect.isFalse(dSet.contains(newC));
+  Expect.isTrue(dSet.contains(c));
+
+  // Remove and length should not be typed.
+  Expect.equals(5, dSet.length);
+  dSet.remove(c); // Success, no type checks.
+  Expect.equals(4, dSet.length);
+}
+
+void testUpcast() {
+  var setEls = new Set<C?>.from(elements);
+  var objectSet = Set.castFrom<C?, Object?>(setEls);
+
+  Expect.listEquals(elements, objectSet.toList());
+
+  var newObject = new Object();
+  Expect.throws(() => objectSet.add(newObject));
+  Expect.isFalse(objectSet.contains(newObject));
+
+  var toSet = objectSet.toSet();
+  Expect.isTrue(toSet is LinkedHashSet<Object?>);
+  Expect.isFalse(toSet is LinkedHashSet<C?>);
+}
+
+void testNewSet() {
+  // Specified custom newSet as empty HashSet.
+  var setEls = new Set<C?>.from(elements);
+  var customNewSet;
+  var objectSet2 = Set.castFrom<C?, Object?>(setEls,
+      newSet: <T>() => customNewSet = new HashSet<T>());
+
+  var customToSet = objectSet2.toSet();
+  Expect.isTrue(customToSet is HashSet<Object?>);
+  Expect.isFalse(customToSet is HashSet<C?>);
+  Expect.identical(customToSet, customNewSet);
+}

tests/corelib/cast_strong_test.dart

@@ -0,0 +1,106 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Requirements=nnbd-strong
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testIterable();
+  testList();
+  testMap();
+  testSet();
+}
+
+testIterable() {
+  var iterable = new Iterable<C?>.generate(elements.length, (n) => elements[n]);
+  var iterableNonNull = Iterable.castFrom<C?, C>(iterable);
+  // Downcast non-nullable.
+
+  // An iterable that (likely) can do direct access.
+  var dIterableDirect = Iterable.castFrom<C, D>(iterableNonNull);
+  Expect.equals(d, dIterableDirect.elementAt(1));
+  // null is not D.
+  Expect.throws(() => dIterableDirect.skip(3).elementAt(1));
+
+  // An iterable that cannot do direct access.
+  var dIterableNonDirect =
+      Iterable.castFrom<C, D>(iterableNonNull.where((_) => true));
+  Expect.equals(d, dIterableNonDirect.elementAt(1));
+  // null is not D.
+  Expect.throws(() => dIterableNonDirect.skip(3).elementAt(1));
+
+  // Iterable that definitely won't survive accessing element 3.
+  var iterableLimited = new Iterable<C?>.generate(
+      elements.length, (n) => n == 3 ? throw "untouchable" : elements[n]);
+  var iterableLimitedNonNull = Iterable.castFrom<C?, C>(iterableLimited);
+  var dIterableLimited = Iterable.castFrom<C, D>(iterableLimitedNonNull);
+  Expect.equals(d, dIterableLimited.elementAt(1));
+  // null is not D.
+  Expect.throws(() => dIterableLimited.skip(3).elementAt(1));
+
+  // Upcast non-nullable.
+  var objectIterable = Iterable.castFrom<C, Object>(iterableNonNull);
+  // null is not Object.
+  Expect.throws(() => objectIterable.skip(3).elementAt(1));
+}
+
+testList() {
+  var list = new List<C?>.from(elements);
+  var listNonNull = List.castFrom<C?, C>(list);
+
+  // Downcast non-nullable.
+  var dList = List.castFrom<C, D>(listNonNull);
+  Expect.equals(d, dList[1]);
+  Expect.throws(() => dList.last); // null is not D.
+
+  // Upcast non-nullable.
+  var objectList = List.castFrom<C, Object>(listNonNull);
+  Expect.throws(() => objectList.last); // null is not Object.
+}
+
+testMap() {
+  var map = new Map.fromIterables(elements, elements);
+  var mapNonNull = Map.castFrom<C?, C?, C, C>(map);
+
+  // Downcast non-nullable.
+  var dMap = Map.castFrom<C, C, D, D>(mapNonNull);
+  Expect.equals(d, dMap[d]);
+  Expect.isTrue(dMap.containsKey(null));
+  Expect.equals(null, dMap[null]);
+
+  // Test keys and values
+  Expect.isTrue(dMap.keys is Iterable<D>);
+  Expect.isTrue(dMap.values is Iterable<D>);
+  Expect.throws(() => dMap.keys.toList());
+  Expect.throws(() => dMap.values.toList());
+
+  // Upcast non-nullable.
+  var objectMap = Map.castFrom<C, C, Object, Object>(mapNonNull);
+  Expect.isTrue(objectMap.containsKey(null));
+  Expect.equals(null, objectMap[null]);
+
+  // Test keys and values
+  Expect.isTrue(objectMap.keys is Iterable<Object>);
+  Expect.isTrue(objectMap.values is Iterable<Object>);
+  // null is not Object.
+  Expect.throws(() => objectMap.keys.toList());
+  Expect.throws(() => objectMap.values.toList());
+}
+
+testSet() {
+  var setEls = new Set<C?>.from(elements);
+  var setNonNull = Set.castFrom<C?, C>(setEls);
+
+  // Downcast non-nullable.
+  var dSet = Set.castFrom<C, D>(setNonNull);
+  Expect.equals(d, dSet.elementAt(1));
+  Expect.throws(() => dSet.last); // null is not D.
+
+  // Upcast non-nullable.
+  var objectSet = Set.castFrom<C, Object>(setNonNull);
+  Expect.throws(() => objectSet.last); // null is not Object.
+}

tests/corelib/cast_test.dart

@@ -1,189 +0,0 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import "dart:collection";
-import "dart:typed_data";
-import "package:expect/expect.dart";
-
-// TODO(rnystrom): Not migrated to NNBD yet.
-// See https://github.com/dart-lang/sdk/issues/39517.
-
-void main() {
-  testIterable();
-  testList();
-}
-
-final elements = <C>[c, d, e, f, null];
-
-void testIterable() {
-  var iterable = new Iterable<C>.generate(elements.length, (n) => elements[n]);
-  // Down-cast
-  {
-    // An iterable that (likely) can do direct access.
-    var dIterable = Iterable.castFrom<C, D>(iterable);
-
-    Expect.throws(() => dIterable.first, null, "1.first");
-    Expect.equals(d, dIterable.elementAt(1));
-    Expect.throws(() => dIterable.elementAt(2), null, "1.2"); // E is not D.
-    Expect.equals(f, dIterable.skip(3).first); // Skip does not access element.
-    Expect.equals(null, dIterable.skip(3).elementAt(1));
-
-    Expect.throws(() => dIterable.toList(), null, "1.toList");
-  }
-
-  {
-    // An iterable that cannot do direct access.
-    var dIterable2 = Iterable.castFrom<C, D>(iterable.where((_) => true));
-
-    Expect.throws(() => dIterable2.first, null, "2.first");
-    Expect.equals(d, dIterable2.elementAt(1));
-    Expect.throws(() => dIterable2.elementAt(2), null, "2.2"); // E is not D.
-    Expect.equals(f, dIterable2.skip(3).first); // Skip does not access element.
-    Expect.equals(null, dIterable2.skip(3).elementAt(1));
-
-    Expect.throws(() => dIterable2.toList(), null, "2.toList");
-  }
-
-  {
-    // Iterable that definitely won't survive accessing element 2.
-    var iterable3 = new Iterable<C>.generate(
-        elements.length, (n) => n == 3 ? throw "untouchable" : elements[n]);
-    var dIterable3 = Iterable.castFrom<C, D>(iterable3);
-
-    Expect.throws(() => dIterable3.first, null, "3.first");
-    Expect.equals(d, dIterable3.elementAt(1));
-    Expect.throws(() => dIterable3.elementAt(3), null, "3.3");
-    // Skip does not access element.
-    Expect.equals(null, dIterable3.skip(4).first);
-    Expect.equals(null, dIterable3.skip(3).elementAt(1));
-
-    Expect.throws(() => dIterable3.toList(), null, "3.toList");
-  }
-
-  // Up-cast.
-  {
-    var oIterable4 = Iterable.castFrom<C, Object>(iterable);
-    Expect.listEquals(elements, oIterable4.toList());
-  }
-}
-
-void testList() {
-  // Down-cast.
-  var list = new List<C>.from(elements);
-  var dList = List.castFrom<C, D>(list);
-
-  Expect.throws(() => dList.first); // C is not D.
-  Expect.equals(d, dList[1]);
-  Expect.throws(() => dList[2]); // E is not D.
-  Expect.equals(f, dList[3]);
-  Expect.equals(null, dList.last);
-
-  Expect.throws(() => dList.toList());
-
-  dList[2] = d;
-  Expect.equals(d, dList[2]); // Setting works.
-
-  // Up-cast.
-  var list2 = new List<C>.from(elements);
-  var dList2 = List.castFrom<C, Object>(list2);
-  Expect.listEquals(elements, dList2);
-  Expect.throws(() => dList2[2] = new Object()); // Cannot set non-C.
-  Expect.listEquals(elements, dList2);
-
-  // Regression test.
-  var list3 = <num>[4, 3, 2, 1];
-  var dList3 = list3.cast<int>();
-  dList3.sort(null);
-  Expect.listEquals([1, 2, 3, 4], list3);
-}
-
-void testSet() {
-  var set = new Set<C>.from(elements); // Linked HashSet.
-  Expect.listEquals(elements, set.toList()); // Preserves order.
-
-  var dSet = Set.castFrom<C, D>(set);
-
-  // Preserves order.
-  Expect.throws(() => dSet.first); // C is not D.
-  Expect.equals(d, dSet.elementAt(1));
-  Expect.throws(() => dSet.elementAt(2)); // E is not D.
-
-  Expect.throws(() => dSet.toList());
-
-  // Contains is not typed.
-  var newC = new C();
-  Expect.isFalse(dSet.contains(newC));
-  dSet.add(newC);
-  Expect.isTrue(dSet.contains(newC));
-
-  Expect.equals(5, dSet.length);
-  dSet.remove(newC);
-  Expect.equals(5, dSet.length);
-  dSet.remove(c); // Success, no type checks.
-  Expect.equals(4, dSet.length);
-
-  // Up-cast
-  var set2 = new Set<C>.from(elements);
-  var dSet2 = Set.castFrom<C, Object>(set2);
-
-  var newObject = new Object();
-  Expect.throws(() => dSet2.add(newObject));
-  Expect.isFalse(dSet.contains(newObject));
-
-  var toSet2 = dSet2.toSet();
-  Expect.isTrue(toSet2 is LinkedHashSet<Object>);
-  Expect.isTrue(toSet2 is! LinkedHashSet<C>);
-
-  // Custom emptySet.
-
-  var set3 = new Set<C>.from(elements);
-  var dSet3 = Set.castFrom<C, Object>(set3, newSet: <T>() => new HashSet<T>());
-
-  var toSet3 = dSet3.toSet();
-  Expect.isTrue(toSet3 is HashSet<Object>);
-  Expect.isTrue(toSet3 is HashSet<C>);
-  Expect.isTrue(toSet3 is! LinkedHashSet<Object>);
-}
-
-void testMap() {
-  var map = new Map.fromIterables(elements, elements);
-
-  var dMap = Map.castFrom<C, C, D, D>(map);
-
-  Expect.isTrue(dMap is Map<D, D>);
-
-  Expect.equals(null, dMap[new C()]);
-  Expect.throws(() => dMap[c]);
-  Expect.isTrue(dMap.containsKey(c));
-  Expect.equals(d, dMap[d]);
-  Expect.throws(() => dMap[e]);
-  Expect.equals(null, dMap[null]);
-
-  Expect.equals(5, dMap.length);
-  dMap.remove(c); // Success, no type checks along the way.
-  Expect.equals(4, dMap.length);
-  Expect.equals(null, dMap[c]);
-
-  Expect.throws(() => dMap[c] = d);
-  Expect.throws(() => dMap[d] = c);
-  Expect.equals(4, dMap.length);
-
-  Expect.isTrue(dMap.keys is Iterable<D>);
-  Expect.isTrue(dMap.values is Iterable<D>);
-  Expect.throws(() => dMap.keys.toList());
-  Expect.throws(() => dMap.values.toList());
-}
-
-class C {}
-
-class D extends C {}
-
-class E extends C {}
-
-class F implements D, E {}
-
-final c = new C();
-final d = new D();
-final e = new E();
-final f = new F();

tests/corelib/cast_weak_test.dart

@@ -0,0 +1,101 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Requirements=nnbd-weak
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testIterable();
+  testList();
+  testMap();
+  testSet();
+}
+
+testIterable() {
+  var iterable = new Iterable<C?>.generate(elements.length, (n) => elements[n]);
+  var iterableNonNull = Iterable.castFrom<C?, C>(iterable);
+  // Downcast non-nullable.
+
+  // An iterable that (likely) can do direct access.
+  var dIterableDirect = Iterable.castFrom<C, D>(iterableNonNull);
+  Expect.equals(d, dIterableDirect.elementAt(1));
+  Expect.equals(null, dIterableDirect.skip(3).elementAt(1));
+
+  // An iterable that cannot do direct access.
+  var dIterableNonDirect =
+      Iterable.castFrom<C, D>(iterableNonNull.where((_) => true));
+  Expect.equals(d, dIterableNonDirect.elementAt(1));
+  Expect.equals(null, dIterableNonDirect.skip(3).elementAt(1));
+
+  // Iterable that definitely won't survive accessing element 3.
+  var iterableLimited = new Iterable<C?>.generate(
+      elements.length, (n) => n == 3 ? throw "untouchable" : elements[n]);
+  var iterableLimitedNonNull = Iterable.castFrom<C?, C>(iterableLimited);
+  var dIterableLimited = Iterable.castFrom<C, D>(iterableLimitedNonNull);
+  Expect.equals(d, dIterableLimited.elementAt(1));
+  Expect.equals(null, dIterableLimited.skip(3).elementAt(1));
+
+  // Upcast non-nullable.
+  var objectIterable = Iterable.castFrom<C, Object>(iterableNonNull);
+  Expect.equals(null, objectIterable.skip(3).elementAt(1));
+}
+
+testList() {
+  var list = new List<C?>.from(elements);
+  var listNonNull = List.castFrom<C?, C>(list);
+
+  // Downcast non-nullable.
+  var dList = List.castFrom<C, D>(listNonNull);
+  Expect.equals(d, dList[1]);
+  Expect.equals(null, dList.last);
+
+  // Upcast non-nullable.
+  var objectList = List.castFrom<C, Object>(listNonNull);
+  Expect.equals(null, objectList.last);
+}
+
+testMap() {
+  var map = new Map.fromIterables(elements, elements);
+  var mapNonNull = Map.castFrom<C?, C?, C, C>(map);
+
+  // Downcast non-nullable.
+  var dMap = Map.castFrom<C, C, D, D>(mapNonNull);
+  Expect.equals(d, dMap[d]);
+  Expect.isTrue(dMap.containsKey(null));
+  Expect.equals(null, dMap[null]);
+
+  // Test keys and values
+  Expect.isTrue(dMap.keys is Iterable<D>);
+  Expect.isTrue(dMap.values is Iterable<D>);
+  Expect.throws(() => dMap.keys.toList());
+  Expect.throws(() => dMap.values.toList());
+
+  // Upcast non-nullable.
+  var objectMap = Map.castFrom<C, C, Object, Object>(mapNonNull);
+  Expect.isTrue(objectMap.containsKey(null));
+  Expect.equals(null, objectMap[null]);
+
+  // Test keys and values
+  Expect.isTrue(objectMap.keys is Iterable<Object>);
+  Expect.isTrue(objectMap.values is Iterable<Object>);
+  var expectedValues = new List<Object>.from(elements);
+  Expect.listEquals(expectedValues, objectMap.values.toList());
+}
+
+testSet() {
+  var setEls = new Set<C?>.from(elements);
+  var setNonNull = Set.castFrom<C?, C>(setEls);
+
+  // Downcast non-nullable.
+  var dSet = Set.castFrom<C, D>(setNonNull);
+  Expect.equals(d, dSet.elementAt(1));
+  Expect.equals(null, dSet.last);
+
+  // Upcast non-nullable.
+  var objectSet = Set.castFrom<C, Object>(setNonNull);
+  Expect.equals(null, objectSet.last);
+}

tests/corelib_2/cast_helper.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+final elements = <C>[c, d, e, f, null];
+
+class C {}
+
+class D extends C {}
+
+class E extends C {}
+
+class F implements D, E {}
+
+final c = C();
+final d = D();
+final e = E();
+final f = F();

tests/corelib_2/cast_iterable_test.dart

@@ -0,0 +1,68 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testDowncastDirectAccess();
+  testDowncastNoDirectAccess();
+  testDowncastUntouchableElements();
+  testUpcast();
+}
+
+void testDowncastDirectAccess() {
+  var iterable = new Iterable<C>.generate(elements.length, (n) => elements[n]);
+
+  // An iterable that (likely) can do direct access.
+  var dIterable = Iterable.castFrom<C, D>(iterable);
+
+  Expect.throws(() => dIterable.first, null, "direct.first");
+  Expect.equals(d, dIterable.elementAt(1));
+  Expect.throws(() => dIterable.elementAt(2), null, "direct.2"); // E is not D.
+  Expect.equals(f, dIterable.skip(3).first); // Skip does not access element.
+  Expect.equals(null, dIterable.skip(3).elementAt(1));
+
+  Expect.throws(() => dIterable.toList(), null, "direct.toList");
+}
+
+void testDowncastNoDirectAccess() {
+  var iterable = new Iterable<C>.generate(elements.length, (n) => elements[n]);
+
+  // An iterable that cannot do direct access.
+  var dIterable = Iterable.castFrom<C, D>(iterable.where((_) => true));
+
+  Expect.throws(() => dIterable.first, null, "nonDirect.first");
+  Expect.equals(d, dIterable.elementAt(1));
+  // E is not D.
+  Expect.throws(() => dIterable.elementAt(2), null, "nonDirect.2");
+  Expect.equals(f, dIterable.skip(3).first); // Skip does not access element.
+  Expect.equals(null, dIterable.skip(3).elementAt(1));
+
+  Expect.throws(() => dIterable.toList(), null, "nonDirect.toList");
+}
+
+void testDowncastUntouchableElements() {
+  // Iterable that definitely won't survive accessing element 3.
+  var iterable = new Iterable<C>.generate(
+      elements.length, (n) => n == 3 ? throw "untouchable" : elements[n]);
+  var dIterable = Iterable.castFrom<C, D>(iterable);
+
+  Expect.throws(() => dIterable.first, null, "untouchable.first");
+  Expect.equals(d, dIterable.elementAt(1));
+  Expect.throws(() => dIterable.elementAt(3), null, "untouchable.3");
+  // Skip does not access element.
+  Expect.equals(null, dIterable.skip(4).first);
+  Expect.equals(null, dIterable.skip(3).elementAt(1));
+
+  Expect.throws(() => dIterable.toList(), null, "untouchable.toList");
+}
+
+void testUpcast() {
+  var iterable = new Iterable<C>.generate(elements.length, (n) => elements[n]);
+
+  var objectIterable = Iterable.castFrom<C, Object>(iterable);
+  Expect.listEquals(elements, objectIterable.toList());
+}

tests/corelib_2/cast_list_test.dart

@@ -0,0 +1,46 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testDowncast();
+  testUpcast();
+  testRegression();
+}
+
+void testDowncast() {
+  var list = new List<C>.from(elements);
+  var dList = List.castFrom<C, D>(list);
+
+  Expect.throws(() => dList.first); // C is not D.
+  Expect.equals(d, dList[1]);
+  Expect.throws(() => dList[2]); // E is not D.
+  Expect.equals(f, dList[3]);
+  Expect.equals(null, dList.last);
+
+  Expect.throws(() => dList.toList());
+
+  // Setting works.
+  dList[2] = d;
+  Expect.equals(d, dList[2]);
+}
+
+void testUpcast() {
+  var list2 = new List<C>.from(elements);
+  var dList2 = List.castFrom<C, Object>(list2);
+  Expect.listEquals(elements, dList2);
+  Expect.throws(() => dList2[2] = new Object()); // Cannot set non-C.
+  Expect.listEquals(elements, dList2);
+}
+
+void testRegression() {
+  var numList = <num>[4, 3, 2, 1];
+  var intList = numList.cast<int>();
+  intList.sort(null);
+  Expect.listEquals([1, 2, 3, 4], numList);
+  Expect.listEquals([1, 2, 3, 4], intList);
+}

tests/corelib_2/cast_map_test.dart

@@ -0,0 +1,62 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testDowncast();
+  testUpcast();
+}
+
+void testDowncast() {
+  var map = new Map.fromIterables(elements, elements);
+  var dMap = Map.castFrom<C, C, D, D>(map);
+
+  Expect.isTrue(dMap is Map<D, D>);
+
+  Expect.equals(null, dMap[new C()]);
+  Expect.throws(() => dMap[c]); // C is not D.
+  Expect.isTrue(dMap.containsKey(c)); // containsKey should not be typed.
+  Expect.equals(d, dMap[d]);
+  Expect.throws(() => dMap[e]); // E is not D.
+  Expect.isTrue(dMap.containsKey(null));
+  Expect.equals(null, dMap[null]);
+
+  Expect.equals(5, dMap.length);
+  Expect.throws(() => dMap.remove(c)); // Removes key but fails to return value.
+  Expect.equals(4, dMap.length);
+  Expect.equals(null, dMap[c]);
+
+  // Runtime errors when assigning or accessing a C.
+  Expect.throws(() => dMap[c] = d);
+  Expect.throws(() => dMap[d] = c);
+  Expect.equals(4, dMap.length);
+
+  // Test keys and values.
+  Expect.isTrue(dMap.keys is Iterable<D>);
+  Expect.isTrue(dMap.values is Iterable<D>);
+  Expect.throws(() => dMap.keys.toList());
+  Expect.throws(() => dMap.values.toList());
+}
+
+void testUpcast() {
+  var map = new Map.fromIterables(elements, elements);
+  var objectMap = Map.castFrom<C, C, Object, Object>(map);
+
+  Expect.equals(5, objectMap.length);
+  Expect.equals(c, objectMap[c]);
+  Expect.isTrue(objectMap.containsKey(c));
+  Expect.equals(c, objectMap.remove(c));
+  Expect.equals(4, objectMap.length);
+
+  // Test keys and values.
+  Expect.isTrue(objectMap.keys is Iterable<Object>);
+  Expect.isTrue(objectMap.values is Iterable<Object>);
+  var expected = new List<Object>.from(elements);
+  expected.remove(c);
+  Expect.listEquals(expected, objectMap.keys.toList());
+  Expect.listEquals(expected, objectMap.values.toList());
+}

tests/corelib_2/cast_set_test.dart

@@ -0,0 +1,73 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import "package:expect/expect.dart";
+import 'cast_helper.dart';
+
+void main() {
+  testOrder();
+  testDowncast();
+  testUpcast();
+  testNewSet();
+}
+
+void testOrder() {
+  var setEls = new Set<C>.from(elements); // Linked HashSet.
+  Expect.listEquals(elements, setEls.toList()); // Preserves order.
+}
+
+void testDowncast() {
+  var setEls = new Set<C>.from(elements);
+  var dSet = Set.castFrom<C, D>(setEls);
+
+  // Preserves order.
+  Expect.throws(() => dSet.first); // C is not D.
+  Expect.equals(d, dSet.elementAt(1));
+  Expect.throws(() => dSet.elementAt(2)); // E is not D.
+  Expect.equals(f, dSet.elementAt(3));
+  Expect.equals(null, dSet.elementAt(4));
+
+  Expect.throws(() => dSet.toList());
+
+  // Contains should not be typed.
+  var newC = new C();
+  Expect.isFalse(dSet.contains(newC));
+  Expect.throws(() => dSet.add(newC));
+  Expect.isFalse(dSet.contains(newC));
+  Expect.isTrue(dSet.contains(c));
+
+  // Remove and length should not be typed.
+  Expect.equals(5, dSet.length);
+  dSet.remove(c); // Success, no type checks.
+  Expect.equals(4, dSet.length);
+}
+
+void testUpcast() {
+  var setEls = new Set<C>.from(elements);
+  var objectSet = Set.castFrom<C, Object>(setEls);
+
+  Expect.listEquals(elements, objectSet.toList());
+
+  var newObject = new Object();
+  Expect.throws(() => objectSet.add(newObject));
+  Expect.isFalse(objectSet.contains(newObject));
+
+  var toSet = objectSet.toSet();
+  Expect.isTrue(toSet is LinkedHashSet<Object>);
+  Expect.isFalse(toSet is LinkedHashSet<C>);
+}
+
+void testNewSet() {
+  // Specified custom newSet as empty HashSet.
+  var setEls = new Set<C>.from(elements);
+  var customNewSet;
+  var objectSet2 = Set.castFrom<C, Object>(setEls,
+      newSet: <T>() => customNewSet = new HashSet<T>());
+
+  var customToSet = objectSet2.toSet();
+  Expect.isTrue(customToSet is HashSet<Object>);
+  Expect.isFalse(customToSet is HashSet<C>);
+  Expect.identical(customToSet, customNewSet);
+}

tests/corelib_2/cast_test.dart

@@ -1,186 +0,0 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import "dart:collection";
-import "dart:typed_data";
-import "package:expect/expect.dart";
-
-void main() {
-  testIterable();
-  testList();
-}
-
-final elements = <C>[c, d, e, f, null];
-
-void testIterable() {
-  var iterable = new Iterable<C>.generate(elements.length, (n) => elements[n]);
-  // Down-cast
-  {
-    // An iterable that (likely) can do direct access.
-    var dIterable = Iterable.castFrom<C, D>(iterable);
-
-    Expect.throws(() => dIterable.first, null, "1.first");
-    Expect.equals(d, dIterable.elementAt(1));
-    Expect.throws(() => dIterable.elementAt(2), null, "1.2"); // E is not D.
-    Expect.equals(f, dIterable.skip(3).first); // Skip does not access element.
-    Expect.equals(null, dIterable.skip(3).elementAt(1));
-
-    Expect.throws(() => dIterable.toList(), null, "1.toList");
-  }
-
-  {
-    // An iterable that cannot do direct access.
-    var dIterable2 = Iterable.castFrom<C, D>(iterable.where((_) => true));
-
-    Expect.throws(() => dIterable2.first, null, "2.first");
-    Expect.equals(d, dIterable2.elementAt(1));
-    Expect.throws(() => dIterable2.elementAt(2), null, "2.2"); // E is not D.
-    Expect.equals(f, dIterable2.skip(3).first); // Skip does not access element.
-    Expect.equals(null, dIterable2.skip(3).elementAt(1));
-
-    Expect.throws(() => dIterable2.toList(), null, "2.toList");
-  }
-
-  {
-    // Iterable that definitely won't survive accessing element 2.
-    var iterable3 = new Iterable<C>.generate(
-        elements.length, (n) => n == 3 ? throw "untouchable" : elements[n]);
-    var dIterable3 = Iterable.castFrom<C, D>(iterable3);
-
-    Expect.throws(() => dIterable3.first, null, "3.first");
-    Expect.equals(d, dIterable3.elementAt(1));
-    Expect.throws(() => dIterable3.elementAt(3), null, "3.3");
-    // Skip does not access element.
-    Expect.equals(null, dIterable3.skip(4).first);
-    Expect.equals(null, dIterable3.skip(3).elementAt(1));
-
-    Expect.throws(() => dIterable3.toList(), null, "3.toList");
-  }
-
-  // Up-cast.
-  {
-    var oIterable4 = Iterable.castFrom<C, Object>(iterable);
-    Expect.listEquals(elements, oIterable4.toList());
-  }
-}
-
-void testList() {
-  // Down-cast.
-  var list = new List<C>.from(elements);
-  var dList = List.castFrom<C, D>(list);
-
-  Expect.throws(() => dList.first); // C is not D.
-  Expect.equals(d, dList[1]);
-  Expect.throws(() => dList[2]); // E is not D.
-  Expect.equals(f, dList[3]);
-  Expect.equals(null, dList.last);
-
-  Expect.throws(() => dList.toList());
-
-  dList[2] = d;
-  Expect.equals(d, dList[2]); // Setting works.
-
-  // Up-cast.
-  var list2 = new List<C>.from(elements);
-  var dList2 = List.castFrom<C, Object>(list2);
-  Expect.listEquals(elements, dList2);
-  Expect.throws(() => dList2[2] = new Object()); // Cannot set non-C.
-  Expect.listEquals(elements, dList2);
-
-  // Regression test.
-  var list3 = <num>[4, 3, 2, 1];
-  var dList3 = list3.cast<int>();
-  dList3.sort(null);
-  Expect.listEquals([1, 2, 3, 4], list3);
-}
-
-void testSet() {
-  var set = new Set<C>.from(elements); // Linked HashSet.
-  Expect.listEquals(elements, set.toList()); // Preserves order.
-
-  var dSet = Set.castFrom<C, D>(set);
-
-  // Preserves order.
-  Expect.throws(() => dSet.first); // C is not D.
-  Expect.equals(d, dSet.elementAt(1));
-  Expect.throws(() => dSet.elementAt(2)); // E is not D.
-
-  Expect.throws(() => dSet.toList());
-
-  // Contains is not typed.
-  var newC = new C();
-  Expect.isFalse(dSet.contains(newC));
-  dSet.add(newC);
-  Expect.isTrue(dSet.contains(newC));
-
-  Expect.equals(5, dSet.length);
-  dSet.remove(newC);
-  Expect.equals(5, dSet.length);
-  dSet.remove(c); // Success, no type checks.
-  Expect.equals(4, dSet.length);
-
-  // Up-cast
-  var set2 = new Set<C>.from(elements);
-  var dSet2 = Set.castFrom<C, Object>(set2);
-
-  var newObject = new Object();
-  Expect.throws(() => dSet2.add(newObject));
-  Expect.isFalse(dSet.contains(newObject));
-
-  var toSet2 = dSet2.toSet();
-  Expect.isTrue(toSet2 is LinkedHashSet<Object>);
-  Expect.isTrue(toSet2 is! LinkedHashSet<C>);
-
-  // Custom emptySet.
-
-  var set3 = new Set<C>.from(elements);
-  var dSet3 = Set.castFrom<C, Object>(set3, newSet: <T>() => new HashSet<T>());
-
-  var toSet3 = dSet3.toSet();
-  Expect.isTrue(toSet3 is HashSet<Object>);
-  Expect.isTrue(toSet3 is HashSet<C>);
-  Expect.isTrue(toSet3 is! LinkedHashSet<Object>);
-}
-
-void testMap() {
-  var map = new Map.fromIterables(elements, elements);
-
-  var dMap = Map.castFrom<C, C, D, D>(map);
-
-  Expect.isTrue(dMap is Map<D, D>);
-
-  Expect.equals(null, dMap[new C()]);
-  Expect.throws(() => dMap[c]);
-  Expect.isTrue(dMap.containsKey(c));
-  Expect.equals(d, dMap[d]);
-  Expect.throws(() => dMap[e]);
-  Expect.equals(null, dMap[null]);
-
-  Expect.equals(5, dMap.length);
-  dMap.remove(c); // Success, no type checks along the way.
-  Expect.equals(4, dMap.length);
-  Expect.equals(null, dMap[c]);
-
-  Expect.throws(() => dMap[c] = d);
-  Expect.throws(() => dMap[d] = c);
-  Expect.equals(4, dMap.length);
-
-  Expect.isTrue(dMap.keys is Iterable<D>);
-  Expect.isTrue(dMap.values is Iterable<D>);
-  Expect.throws(() => dMap.keys.toList());
-  Expect.throws(() => dMap.values.toList());
-}
-
-class C {}
-
-class D extends C {}
-
-class E extends C {}
-
-class F implements D, E {}
-
-final c = new C();
-final d = new D();
-final e = new E();
-final f = new F();