Generate tear-off closures dynamically.

dart/sdk/lib/_internal/lib/js_helper.dart

Index: dart/sdk/lib/_internal/lib/js_helper.dart
diff --git a/dart/sdk/lib/_internal/lib/js_helper.dart b/dart/sdk/lib/_internal/lib/js_helper.dart
index e346734f1b13f6f0b4f5e06622b5d618d70c3138..21789e2a792dd3a1e8514be2429ce07d9befc3da 100644
--- a/dart/sdk/lib/_internal/lib/js_helper.dart
+++ b/dart/sdk/lib/_internal/lib/js_helper.dart
@@ -1553,9 +1553,70 @@ convertDartClosureToJS(closure, int arity) {
  * Super class for Dart closures.
  */
 class Closure implements Function {
+  // TODO(ahe): These constants must be in sync with
+  // reflection_data_parser.dart.
+  static const FUNCTION_INDEX = 0;
+  static const NAME_INDEX = 1;
+  static const CALL_NAME_INDEX = 2;
+  static const REQUIRED_PARAMETER_INDEX = 3;
+  static const OPTIONAL_PARAMETER_INDEX = 4;
+  static const DEFAULT_ARGUMENTS_INDEX = 5;
+
+  Closure();
+
+  /**
+   * Creates a closure for use by implicit getters associated with a method.
+   *
+   * In other words, creates a tear-off closure.
+   *
+   * Called from [closureFromTearOff] as well as from reflection when tearing
+   * of a method via [:getField:].
+   *
+   * This method assumes that [array] was created by
+   * [dart2js.js_emitter.ContainerBuilder.addMemberMethod].
+   */
+  factory Closure.fromTearOff(receiver, List array, bool isStatic) {
+    var function = array[FUNCTION_INDEX];
+    String name = array[NAME_INDEX];
+    String callName = array[CALL_NAME_INDEX];
+    int requiredParameterCount = array[REQUIRED_PARAMETER_INDEX] - 1;
+    bool isReflectable = requiredParameterCount != -1;
+    int optionalParameterCount = array[OPTIONAL_PARAMETER_INDEX];
+    int index = DEFAULT_ARGUMENTS_INDEX + optionalParameterCount;
+
+    // Create a closure and "monkey" patch it with call stubs.
+    Closure closure = new Closure();
+    JS('', '#[#] = #', closure, callName,
+       isStatic ? function : forwardTo(receiver, function));
+    while (index < array.length) {
+      if (!JS('bool', 'typeof # == "function"', array[index])) break;
+      var stub = array[index++];
+      var stubName = array[index++];
+      var stubCallName = array[index++];
+      JS('', '#[#] = #', closure, stubCallName,
+         isStatic ? stub : forwardTo(receiver, stub));
+    }
+
+    return closure;
+  }
+
+  static forwardTo(receiver, function) {
+    return JS(
+        '',
+        'function(r,f){return function(){return f.apply(r,arguments)}}(#,#)',
+        receiver, function);
+  }
+
   String toString() => "Closure";
 }
 
+/// Called from implicit method getter (aka tear-off).
+Closure closureFromTearOff(receiver, jsArray, isStatic) {
+  return new Closure.fromTearOff(
+      receiver, JS('JSExtendableArray', '#', jsArray),
+      JS('bool', '!!#', isStatic));
+}
+
 /// Represents a 'tear-off' closure, that is an instance method bound
 /// to a specific receiver (instance).
 class BoundClosure extends Closure {