Warnings for instantiating an abstract type.

frog/type.dart

Index: frog/type.dart
diff --git a/frog/type.dart b/frog/type.dart
index 8399dcc398ffa2b41839ccff3b2970df7ab090f4..237d6c54c681ef8be1544eec9d12871e6758b019 100644
--- a/frog/type.dart
+++ b/frog/type.dart
@@ -91,7 +91,10 @@ class Type implements Named, Hashable {
 
   set jsname(String name) => _jsname = name;
 
+  /** The members directly on this type. */
+  // TODO(jmesserly): should this be directMembers?
   Map<String, Member> get members() => null;
+
   Definition get definition() => null;
   FactoryMap get factories() => null;
 
@@ -108,6 +111,47 @@ class Type implements Named, Hashable {
 
   int hashCode() => name.hashCode();
 
+  bool _isAbstract;
+  bool get isAbstract() {
+    if (_isAbstract == null) {
+      if (isClass) {
+        _isAbstract = inheritedMembers.getValues().some((m) => m.isAbstract);
+      } else {
+        _isAbstract = true;
+      }
+    }
+    return _isAbstract;
+  }
+
+  Map<String, Member> _inheritedMembers;
+  /**
+   * Gets all members in the class with the corresponding most-derived
+   * member.
+   */
+  // TODO(jmesserly): use this for getMember and do _checkOverride here?
+  Map<String, Member> get inheritedMembers() {
+    if (_inheritedMembers == null) {
+      _inheritedMembers = _getInheritedMembers(<String, Member>{});
+    }
+    return _inheritedMembers;
+  }
+
+  _getInheritedMembers(Map<String, Member> flattened) {
+    if (interfaces != null) {
+      for (var i in interfaces) {
+        i._getInheritedMembers(flattened);
+      }
+    }
+    if (parent != null) {
+      parent._getInheritedMembers(flattened);
+    }
+    // Add my members last so they take precedence
+    for (var m in getAllMembers().getValues()) {
+      flattened[m.name] = m;
+    }
+    return flattened;
+  }
+
   void _checkOverride(Member member) {
     // always look in parents to check that any overloads are legal
     var parentMember = _getMemberInParents(member.name);