Sdk: DDC: Abstract getter or setter overrides declared in class clobber inherited concrete implementations

Created on 16 Jun 2017 · 9Comments · Source: dart-lang/sdk

Declaring abstract getters that override implementations from mixins or superclasses results in the getter being undefined when compiled in the dev compiler.

This issue is also present in the reverse, for setters: declaring abstract setters results in the setter being undefined, which actually throws.

Declaring both abstract getters and setters avoids the issue.

Example:

main() {
  // Abstract getter declared after concrete impl from mixin
  var instance1 = new Class1()..foo = 'bar';
  print(instance1.foo); // null

  // Abstract getter declared after concrete impl from superclass
  // Subclasses of this also fail
  var instance2 = new Class2()..foo = 'bar';
  print(instance2.foo); // null

  // Abstract getter declared in mixin after concrete impl from superclass
  var instance3 = new Class3()..foo = 'bar';
  print(instance3.foo); // bar

  // Abstract getter declared in interface after concrete impl from superclass
  var instance4 = new Class4()..foo = 'bar';
  print(instance4.foo); // bar

  // Mixin overriding abstract getter declared in superclass, which is declared after concrete impl from mixin
  var instance5 = new Class5()..foo = 'bar';
  print(instance5.foo); // bar
}

abstract class GetterAbstract {
  get foo;
}

class GetterConcrete {
  var _foo;

  get foo => _foo;
  set foo(value) => _foo = value;
}

class Class1 extends Object with GetterConcrete {
  get foo;
}

class Class2 extends GetterConcrete {
  get foo;
}

class Class3 extends GetterConcrete with GetterAbstract {}

class Class4 extends GetterConcrete implements GetterAbstract {}

abstract class _Helper_Class5 extends GetterConcrete {
  get foo;
}
class Class5 extends _Helper_Class5 with GetterConcrete {}

This is caused by the setter being redefined for these classes, but not the getter:

  list__main.Class2 = class Class2 extends list__main.GetterConcrete {
    set foo(value) {
      super.foo = value;
    }
  };
  (list__main.Class2.new = function() {
    list__main.Class2.__proto__.new.call(this);
  }).prototype = list__main.Class2.prototype;

You can see this issue in this ES6 reduced test case:

class A {
  get foo() {
    return 'foo'
  }
  set foo(value) {}
}

class B extends A {}

class C extends A {
  set foo(value) {}
}

var b = new B();
console.log(b.foo); // 'foo'

var c = new C();
console.log(c.foo); // undefined

We frequently use this pattern of overriding getters in order to update doc comments for subclasses, so it's unfortunate that this is a problem.

This issue is present in Dart 1.24.0 and 1.25.0-dev.1.0

P1 type-bug web-dev-compiler

Source