Better casting of for-in loops.

pkg/analyzer/lib/src/generated/error_verifier.dart

 // Copyright (c) 2014, 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 analyzer.src.generated.error_verifier;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 5676 matching lines @@
 
     // Use an explicit string instead of [loopType] to remove the "<E>".
     String loopTypeName = node.awaitKeyword != null ? "Stream" : "Iterable";
 
     // The object being iterated has to implement Iterable<T> for some T that
     // is assignable to the variable's type.
     // TODO(rnystrom): Move this into mostSpecificTypeArgument()?
     iterableType = iterableType.resolveToBound(_typeProvider.objectType);
     DartType bestIterableType =
         _typeSystem.mostSpecificTypeArgument(iterableType, loopType);
+
+    // Allow it to be a supertype of Iterable<T> (basically just Object) and do
+    // an implicit downcast to Iterable<dynamic>.
+    if (bestIterableType == null) {
+      if (_typeSystem.isSubtypeOf(loopType, iterableType)) {
+        bestIterableType = DynamicTypeImpl.instance;
+      }
+    }
+
     if (bestIterableType == null) {
       _errorReporter.reportTypeErrorForNode(
           StaticTypeWarningCode.FOR_IN_OF_INVALID_TYPE,
           node.iterable,
           [iterableType, loopTypeName]);
     } else if (!_typeSystem.isAssignableTo(bestIterableType, variableType)) {
       _errorReporter.reportTypeErrorForNode(
           StaticTypeWarningCode.FOR_IN_OF_INVALID_ELEMENT_TYPE,
           node.iterable,
           [iterableType, loopTypeName, variableType]);
@@ skipping 607 matching lines @@
 class _InvocationCollector extends RecursiveAstVisitor {
   final List<String> superCalls = <String>[];
 
   @override
   visitMethodInvocation(MethodInvocation node) {
     if (node.target is SuperExpression) {
       superCalls.add(node.methodName.name);
     }
   }
 }