Add support for binding 'this'

pkg/kernel/lib/interpreter/interpreter.dart

 // Copyright (c) 2017, 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.
 library kernel.interpreter;
 
 import '../ast.dart';
 import '../ast.dart' as ast show Class;
 
 import '../log.dart';
 export '../log.dart';
@@ skipping 35 matching lines @@
   final VariableDeclaration variable;
   final Location location;
 
   Binding(this.variable, this.location);
 }
 
 class Environment {
   final List<Binding> bindings = <Binding>[];
   final Environment parent;
 
+  Value get thisInstance {
+    return containsThis()
+        ? lookupThis().value
+        : throw "Invalid reference to 'this' expression";
+  }
+
   Environment.empty() : parent = null;
   Environment(this.parent);
 
   bool contains(VariableDeclaration variable) {
     for (Binding b in bindings.reversed) {
       if (identical(b.variable, variable)) return true;
     }
     return parent?.contains(variable) ?? false;
   }
 
+  bool containsThis() {
+    for (Binding b in bindings.reversed) {

[Dmitry Stefantsov, 2017/07/14 00:43:08]

Is it important that [bindings] is reversed?

[zhivkag, 2017/07/14 07:02:31]

Done.

+      if (identical(b.variable.name, 'this')) return true;
+    }
+    return parent?.containsThis() ?? false;
+  }
+
   Binding lookupBinding(VariableDeclaration variable) {
     assert(contains(variable));
     for (Binding b in bindings) {
       if (identical(b.variable, variable)) return b;
     }
     return parent.lookupBinding(variable);
   }
 
+  Location lookupThis() {
+    assert(containsThis());

[Dmitry Stefantsov, 2017/07/14 00:43:07]

If we pass this `assert`, then at some iteration of the following loop we'll
return some location, and `parent.lookupThis()` will never be executed.

[zhivkag, 2017/07/14 07:02:31]

The intent of this assert is similar to "contains" for normal variables
declarations: check if `this` is bound in the current environment or any of its
parents.
When the assert passes, a location will eventually be returned, but not
necessarily from the loop below, it could also be with `parent.lookupThis()`.

[Dmitry Stefantsov, 2017/07/18 10:45:15]

Yep.  I misinterpreted [containsThis] above.  Thanks for the clarification!

+    for (Binding b in bindings) {
+      if (identical(b.variable.name, 'this')) return b.location;
+    }
+    return parent.lookupThis();
+  }
+
   Value lookup(VariableDeclaration variable) {
     return lookupBinding(variable).location.value;
   }
 
   void assign(VariableDeclaration variable, Value value) {
     assert(contains(variable));
     lookupBinding(variable).location.value = value;
   }
 
   Environment extend(VariableDeclaration variable, Value value) {
     assert(!contains(variable));
     return new Environment(this)
       ..bindings.add(new Binding(variable, new Location(value)));
   }
+
+  Environment extendWithThis(ObjectValue v) {
+    assert(!containsThis());
+    return extend(new VariableDeclaration('this'), v);
+  }
 }
 
 /// Evaluate expressions.
 class Evaluator extends ExpressionVisitor1<Configuration, EvalConfiguration> {
   Configuration eval(Expression expr, EvalConfiguration config) =>
       expr.accept1(this, config);
 
   Configuration evalList(List<InterpreterExpression> list, Environment env,
       ApplicationContinuation cont) {
     if (list.isNotEmpty) {
@@ skipping 1184 matching lines @@
 void _initializeNullFields(Class class_, ObjectValue newObject) {
   int superClassSize = class_.superclass?.instanceSize ?? 0;
   for (int i = superClassSize; i < class_.instanceSize; i++) {
     Field field = class_.instanceFields[i];
     if (class_.getProperty(newObject, field) == null) {
       assert(field.initializer == null);
       class_.setProperty(newObject, field, Value.nullInstance);
     }
   }
 }