implement null aware ops, fixes #249

test/codegen/language/if_null_assignment_behavior_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 semantics of the ??= operator, including order of operations, by
+// keeping track of the operations performed.
+
+import "package:expect/expect.dart";
+import "if_null_assignment_helper.dart" as h;
+
+bad() {
+  Expect.fail('Should not be executed');
+}
+
+var xGetValue = null;
+
+get x {
+  h.operations.add('x');
+  var tmp = xGetValue;
+  xGetValue = null;
+  return tmp;
+}
+
+void set x(value) {
+  h.operations.add('x=$value');
+}
+
+var yGetValue = null;
+
+get y {
+  h.operations.add('y');
+  var tmp = yGetValue;
+  yGetValue = null;
+  return tmp;
+}
+
+void set y(value) {
+  h.operations.add('y=$value');
+}
+
+var zGetValue = null;
+
+get z {
+  h.operations.add('z');
+  var tmp = zGetValue;
+  zGetValue = null;
+  return tmp;
+}
+
+void set z(value) {
+  h.operations.add('z=$value');
+}
+
+var fValue = null;
+
+f() {
+  h.operations.add('f()');
+  var tmp = fValue;
+  fValue = null;
+  return tmp;
+}
+
+void check(expectedValue, f(), expectedOperations) {
+  Expect.equals(expectedValue, f());
+  Expect.listEquals(expectedOperations, h.operations);
+  h.operations = [];
+}
+
+void checkThrows(expectedException, f(), expectedOperations) {
+  Expect.throws(f, expectedException);
+  Expect.listEquals(expectedOperations, h.operations);
+  h.operations = [];
+}
+
+noMethod(e) => e is NoSuchMethodError;
+
+class C {
+  final String s;
+
+  C(this.s);
+
+  @override
+  String toString() => s;
+
+  static var xGetValue = null;
+
+  static get x {
+    h.operations.add('C.x');
+    var tmp = xGetValue;
+    xGetValue = null;
+    return tmp;
+  }
+
+  static void set x(value) {
+    h.operations.add('C.x=$value');
+  }
+
+  var vGetValue = null;
+
+  get v {
+    h.operations.add('$s.v');
+    var tmp = vGetValue;
+    vGetValue = null;
+    return tmp;
+  }
+
+  void set v(value) {
+    h.operations.add('$s.v=$value');
+  }
+
+  var indexGetValue = null;
+
+  operator[](index) {
+    h.operations.add('$s[$index]');
+    var tmp = indexGetValue;
+    indexGetValue = null;
+    return tmp;
+  }
+
+  void operator[]=(index, value) {
+    h.operations.add('$s[$index]=$value');
+  }
+
+  final finalOne = 1;
+  final finalNull = null;
+
+  void instanceTest() {
+    // v ??= e is equivalent to ((x) => x == null ? v = e : x)(v)
+    vGetValue = 1; check(1, () => v ??= bad(), ['$s.v']); /// 01: ok
+    yGetValue = 1; check(1, () => v ??= y, ['$s.v', 'y', '$s.v=1']); /// 02: ok
+    check(1, () => finalOne ??= bad(), []); /// 03: static type warning
+    yGetValue = 1; checkThrows(noMethod, () => finalNull ??= y, ['y']); /// 04: static type warning
+  }
+}
+
+class D extends C {
+  D(String s) : super(s);
+
+  get v => bad();
+
+  void set v(value) {
+    bad();
+  }
+
+  void derivedInstanceTest() {
+    // super.v ??= e is equivalent to
+    // ((x) => x == null ? super.v = e : x)(super.v)
+    vGetValue = 1; check(1, () => super.v ??= bad(), ['$s.v']); /// 05: ok
+    yGetValue = 1; check(1, () => super.v ??= y, ['$s.v', 'y', '$s.v=1']); /// 06: ok
+  }
+}
+
+main() {
+  // Make sure the "none" test fails if "??=" is not implemented.  This makes
+  // status files easier to maintain.
+  var _; _ ??= null;
+
+  new C('c').instanceTest();
+  new D('d').derivedInstanceTest();
+
+  // v ??= e is equivalent to ((x) => x == null ? v = e : x)(v)
+  xGetValue = 1; check(1, () => x ??= bad(), ['x']); /// 07: ok
+  yGetValue = 1; check(1, () => x ??= y, ['x', 'y', 'x=1']); /// 08: ok
+  h.xGetValue = 1; check(1, () => h.x ??= bad(), ['h.x']); /// 09: ok
+  yGetValue = 1; check(1, () => h.x ??= y, ['h.x', 'y', 'h.x=1']); /// 10: ok
+  { var l = 1; check(1, () => l ??= bad(), []); } /// 11: ok
+  { var l; yGetValue = 1; check(1, () => l ??= y, ['y']); Expect.equals(1, l); } /// 12: ok
+  { final l = 1; check(1, () => l ??= bad(), []); } /// 13: static type warning
+  { final l = null; yGetValue = 1; checkThrows(noMethod, () => l ??= y, ['y']); } /// 14: static type warning
+  check(C, () => C ??= bad(), []); /// 15: static type warning
+  h ??= null; /// 29: compile-time error
+  h[0] ??= null; /// 30: compile-time error
+
+  // C.v ??= e is equivalent to ((x) => x == null ? C.v = e : x)(C.v)
+  C.xGetValue = 1; check(1, () => C.x ??= bad(), ['C.x']); /// 16: ok
+  yGetValue = 1; check(1, () => C.x ??= y, ['C.x', 'y', 'C.x=1']); /// 17: ok
+  h.C.xGetValue = 1; check(1, () => h.C.x ??= bad(), ['h.C.x']); /// 18: ok
+  yGetValue = 1; check(1, () => h.C.x ??= y, ['h.C.x', 'y', 'h.C.x=1']); /// 19: ok
+
+  // e1.v ??= e2 is equivalent to
+  // ((x) => ((y) => y == null ? x.v = e2 : y)(x.v))(e1)
+  xGetValue = new C('x'); xGetValue.vGetValue = 1; /// 20: ok
+  check(1, () => x.v ??= bad(), ['x', 'x.v']);     /// 20: continued
+  xGetValue = new C('x'); yGetValue = 1;                /// 21: ok
+  check(1, () => x.v ??= y, ['x', 'x.v', 'y', 'x.v=1']); /// 21: continued
+  fValue = new C('f()'); fValue.vGetValue = 1;       /// 22: ok
+  check(1, () => f().v ??= bad(), ['f()', 'f().v']); /// 22: continued
+  fValue = new C('f()'); yGetValue = 1;                          /// 23: ok
+  check(1, () => f().v ??= y, ['f()', 'f().v', 'y', 'f().v=1']); /// 23: continued
+
+  // e1[e2] ??= e3 is equivalent to
+  // ((a, i) => ((x) => x == null ? a[i] = e3 : x)(a[i]))(e1, e2)
+  xGetValue = new C('x'); yGetValue = 1; xGetValue.indexGetValue = 2; /// 24: ok
+  check(2, () => x[y] ??= bad(), ['x', 'y', 'x[1]']);                 /// 24: continued
+  xGetValue = new C('x'); yGetValue = 1; zGetValue = 2;          /// 25: ok
+  check(2, () => x[y] ??= z, ['x', 'y', 'x[1]', 'z', 'x[1]=2']); /// 25: continued
+
+  // e1?.v ??= e2 is equivalent to ((x) => x == null ? null : x.v ??= e2)(e1).
+  check(null, () => x?.v ??= bad(), ['x']); /// 26: ok
+  xGetValue = new C('x'); xGetValue.vGetValue = 1; /// 27: ok
+  check(1, () => x?.v ??= bad(), ['x', 'x.v']);     /// 27: continued
+  xGetValue = new C('x'); yGetValue = 1;                 /// 28: ok
+  check(1, () => x?.v ??= y, ['x', 'x.v', 'y', 'x.v=1']); /// 28: continued
+
+  // C?.v ??= e2 is equivalent to C.v ??= e2.
+  C.xGetValue = 1;                         /// 29: ok
+  check(1, () => C?.x ??= bad(), ['C.x']); /// 29: continued
+  h.C.xgetValue = 1;                           /// 30: ok
+  check(1, () => h.c?.x ??= bad(), ['h.C.x']); /// 30: continued
+  yGetValue = 1;                                     /// 31: ok
+  check(1, () => C?.x ??= y, ['C.x', 'y', 'C.x=1']); /// 31: continued
+  yGetValue = 1;                                           /// 32: ok
+  check(1, () => h.C?.x ??= y, ['h.C.x', 'y', 'h.C.x=1']); /// 32: continued
+}