Migrate block 116.

tests/language_2/if_null_precedence_test.dart

 // Copyright (c) 2015, 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.
 
 // Verify that '??' binds tighter than '?:' and less tightly than '||'.
 
 import "package:expect/expect.dart";
 
-assertionError(e) => e is AssertionError;
-
-// Determine whether the VM is running in checked mode.
-bool get checkedMode {
-  try {
-    var x = 'foo';
-    int y = x;
-    return false;
-  } catch (_) {
-    return true;
-  }
-}
-
 main() {
   // Make sure the "none" test fails if "??" is not implemented.  This makes
   // status files easier to maintain.
   var _ = null ?? null;
 
   // "a ?? b ?? c" should be legal, and should evaluate to the first non-null
   // value (or null if there are no non-null values).
-  Expect.equals(1, 1 ?? 2 ?? 3); //# 01: ok
-  Expect.equals(2, null ?? 2 ?? 3); //# 02: ok
-  Expect.equals(3, null ?? null ?? 3); //# 03: ok
-  Expect.equals(null, null ?? null ?? null); //# 04: ok
+  Expect.equals(1, 1 ?? 2 ?? 3);
+  Expect.equals(2, null ?? 2 ?? 3);
+  Expect.equals(3, null ?? null ?? 3);
+  Expect.equals(null, null ?? null ?? null);
 
   // "a ?? b ? c : d" should parse as "(a ?? b) ? c : d", therefore provided
   // that a is true, b need not be a bool.  An incorrect parse of
   // "a ?? (b ? c : d)" would require b to be a bool to avoid a static type
   // warning.
-  Expect.equals(2, true ?? 1 ? 2 : 3); //# 05: ok
+  Expect.equals(2, true ?? 1 ? 2 : 3);

[Lasse Reichstein Nielsen, 2017/08/29 07:43:40]

Should this be a type problem in Dart 2? 
Or is it an implicit downcast from Object to bool of (true ?? 1)?

[Bob Nystrom, 2017/08/30 18:21:23]

Yes, I believe that's right. You get Object as the LUB of true and 1, then
downcast in the Boolean conversion for ?:.

 
   // "a ?? b || c" should parse as "a ?? (b || c)", therefore it's a static
   // type warning if b doesn't have type bool.  An incorrect parse of
   // "(a ?? b) || c" would allow b to have any type provided that a is bool.
-  Expect.equals(false, false ?? 1 || true); //# 06: static type warning
+  false ?? 1 || true; //# 06: compile-time error
 
   // "a || b ?? c" should parse as "(a || b) ?? c", therefore it is a static
   // type warning if b doesn't have type bool.  An incorrect parse of
   // "a || (b ?? c)" would allow b to have any type provided that c is bool.
-  if (checkedMode) {
-    Expect.throws(() => false || 1 ?? true, assertionError); //# 07: static type warning
-  } else {
-    Expect.equals(false, false || 1 ?? true); //               //# 07: continued
-  }
+  false || 1 ?? true; //# 07: compile-time error
 
-  if (checkedMode) {
-    // An incorrect parse of "a || (b ?? c)" would result in no checked-mode
-    // error.
-    Expect.throws(() => false || null ?? true, assertionError); //# 08: ok
-  } else {
-    // An incorrect parse of "a || (b ?? c)" would result in c being evaluated.
-    int i = 0; //                                                 //# 08: continued
-    Expect.equals(false, false || null ?? i++ == 0); //           //# 08: continued
-    Expect.equals(0, i); //                                       //# 08: continued
-  }
+  // An incorrect parse of "a || (b ?? c)" would result in no checked-mode
+  // error.
+  Expect.throwsAssertionError(() => false || null ?? true);
 }