implement null aware ops, fixes #249

test/codegen/language/if_null_assignment_static_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 the static type of a ??= b is the least upper bound of the
+// static types of a and b.
+
+import "package:expect/expect.dart";
+
+// Determine whether the VM is running in checked mode.
+// TODO(jmesserly): changed this to the DDC-friendly pattern.
+bool get checkedMode {
+  bool checked = false;
+  assert((checked = true));
+  return checked;
+}
+
+noMethod(e) => e is NoSuchMethodError;
+
+bad() {
+  Expect.fail('Should not be executed');
+}
+
+class A {
+  String a;
+}
+
+class B extends A {
+  String b;
+}
+
+class C extends A {
+  String c;
+}
+
+A get a => null;
+
+void set a(A value) {}
+
+B get b => null;
+
+void set b(B value) {}
+
+class ClassWithStaticGetters {
+  static A get a => null;
+
+  static void set a(A value) {}
+
+  static B get b => null;
+
+  static void set b(B value) {}
+}
+
+class ClassWithInstanceGetters {
+  A get a => null;
+
+  void set a(A value) {}
+
+  B get b => null;
+
+  void set b(B value) {}
+}
+
+class DerivedClass extends ClassWithInstanceGetters {
+  A get a => bad();
+
+  void set a(A value) { bad(); }
+
+  B get b => bad();
+
+  void set b(B value) { bad(); }
+
+  void derivedTest() {
+    // The static type of super.v ??= e is the LUB of the static types of
+    // super.v and e.
+    (super.a ??= new A()).a; /// 01: ok
+    Expect.throws(() => (super.a ??= new A()).b, noMethod); /// 02: static type warning
+    (super.a ??= new B()).a; /// 03: ok
+    (super.a ??= new B()).b; /// 04: static type warning
+    if (!checkedMode) {
+      (super.b ??= new A()).a; /// 05: ok
+      Expect.throws(() => (super.b ??= new A()).b, noMethod); /// 06: static type warning
+
+      // Exactly the same static warnings that would be caused by super.v = e
+      // are also generated in the case of super.v ??= e.
+      super.b ??= new C(); /// 07: static type warning
+    }
+  }
+}
+
+main() {
+  // Make sure the "none" test fails if "??=" is not implemented.  This makes
+  // status files easier to maintain.
+  var _; _ ??= null;
+
+  new DerivedClass().derivedTest();
+
+  // The static type of v ??= e is the LUB of the static types of v and e.
+  (a ??= new A()).a; /// 08: ok
+  Expect.throws(() => (a ??= new A()).b, noMethod); /// 09: static type warning
+  (a ??= new B()).a; /// 10: ok
+  (a ??= new B()).b; /// 11: static type warning
+  if (!checkedMode) {
+    (b ??= new A()).a; /// 12: ok
+    Expect.throws(() => (b ??= new A()).b, noMethod); /// 13: static type warning
+
+    // Exactly the same static warnings that would be caused by v = e are also
+    // generated in the case of v ??= e.
+    b ??= new C(); /// 14: static type warning
+  }
+
+  // The static type of C.v ??= e is the LUB of the static types of C.v and e.
+  (ClassWithStaticGetters.a ??= new A()).a; /// 15: ok
+  Expect.throws(() => (ClassWithStaticGetters.a ??= new A()).b, noMethod); /// 16: static type warning
+  (ClassWithStaticGetters.a ??= new B()).a; /// 17: ok
+  (ClassWithStaticGetters.a ??= new B()).b; /// 18: static type warning
+  if (!checkedMode) {
+    (ClassWithStaticGetters.b ??= new A()).a; /// 19: ok
+    Expect.throws(() => (ClassWithStaticGetters.b ??= new A()).b, noMethod); /// 20: static type warning
+
+    // Exactly the same static warnings that would be caused by C.v = e are
+    // also generated in the case of C.v ??= e.
+    ClassWithStaticGetters.b ??= new C(); /// 21: static type warning
+  }
+
+  // The static type of e1.v ??= e2 is the LUB of the static types of e1.v and
+  // e2.
+  (new ClassWithInstanceGetters().a ??= new A()).a; /// 22: ok
+  Expect.throws(() => (new ClassWithInstanceGetters().a ??= new A()).b, noMethod); /// 23: static type warning
+  (new ClassWithInstanceGetters().a ??= new B()).a; /// 24: ok
+  (new ClassWithInstanceGetters().a ??= new B()).b; /// 25: static type warning
+  if (!checkedMode) {
+    (new ClassWithInstanceGetters().b ??= new A()).a; /// 26: ok
+    Expect.throws(() => (new ClassWithInstanceGetters().b ??= new A()).b, noMethod); /// 27: static type warning
+
+    // Exactly the same static warnings that would be caused by e1.v = e2 are
+    // also generated in the case of e1.v ??= e2.
+    new ClassWithInstanceGetters().b ??= new C(); /// 28: static type warning
+  }
+
+  // The static type of e1[e2] ??= e3 is the LUB of the static types of e1[e2]
+  // and e3.
+  ((<A>[null])[0] ??= new A()).a; /// 29: ok
+  Expect.throws(() => ((<A>[null])[0] ??= new A()).b, noMethod); /// 30: static type warning
+  ((<A>[null])[0] ??= new B()).a; /// 31: ok
+  ((<A>[null])[0] ??= new B()).b; /// 32: static type warning
+  if (!checkedMode) {
+    ((<B>[null])[0] ??= new A()).a; /// 33: ok
+    Expect.throws(() => ((<B>[null])[0] ??= new A()).b, noMethod); /// 34: static type warning
+
+    // Exactly the same static warnings that would be caused by e1[e2] = e3 are
+    // also generated in the case of e1[e2] ??= e3.
+    (<B>[null])[0] ??= new C(); /// 35: static type warning
+  }
+
+  // The static type of e1?.v op= e2 is the static type of e1.v op e2,
+  // therefore the static type of e1?.v ??= e2 is the static type of
+  // e1.v ?? e2, which is the LUB of the static types of e1?.v and e2.
+  (new ClassWithInstanceGetters()?.a ??= new A()).a; /// 36: ok
+  Expect.throws(() => (new ClassWithInstanceGetters()?.a ??= new A()).b, noMethod); /// 37: static type warning
+  (new ClassWithInstanceGetters()?.a ??= new B()).a; /// 38: ok
+  (new ClassWithInstanceGetters()?.a ??= new B()).b; /// 39: static type warning
+  if (!checkedMode) {
+    (new ClassWithInstanceGetters()?.b ??= new A()).a; /// 40: ok
+    Expect.throws(() => (new ClassWithInstanceGetters()?.b ??= new A()).b, noMethod); /// 41: static type warning
+
+    // Exactly the same static warnings that would be caused by e1.v ??= e2 are
+    // also generated in the case of e1?.v ??= e2.
+    new ClassWithInstanceGetters()?.b ??= new C(); /// 42: static type warning
+  }
+}