Warnings for instantiating an abstract type.

frog/member.dart

 // Copyright (c) 2011, 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.
 
 /** A formal parameter to a [Method]. */
 class Parameter {
   FormalNode definition;
 
   String name;
   Type type;
@@ skipping 987 matching lines @@
       Value target, Arguments args, argsString) {
     declaringType.markUsed();
 
     if (!target.isType) {
       // initializer call to another constructor
       var code = (constructorName != '')
           ? '${declaringType.jsname}.${constructorName}\$ctor.call($argsString)'
           : '${declaringType.jsname}.call($argsString)';
       return new Value(target.type, code, node.span);
     } else {
+      if (declaringType.isAbstract) {
+        // Warn at the constructor location
+        world.warning('Cannot instantiate abstract class ${declaringType.name}',
+            node.span);
+
+        // Now make a message explaining why the type is abstract.
+
+        // Get abstract members grouped by type
+        var members = groupBy(declaringType.inheritedMembers.getValues().filter(
+            (m) => m.isAbstract), (m) => m.declaringType);
+
+        var msg = new StringBuffer('Type ${declaringType.name} is abstract '
+            + 'because it does not implement the following members');
+
+        var types = members.getKeys();
+        types.sort((x, y) => x.name.compareTo(y.name));
+        for (var type in types) {
+          if (type != types[0]) msg.add(';');
+          msg.add(' from type ${type.name}: ');
+          msg.add(Strings.join(map(members[type], (m) => m.name), ', '));
+        }
+
+        // Warn at the type's location
+        world.warning(msg.toString(), declaringType.span);
+      }
+
       var code = (constructorName != '')
           ? 'new ${declaringType.jsname}.${constructorName}\$ctor($argsString)'
           : 'new ${declaringType.jsname}($argsString)';
       // TODO(jmesserly): using the "node" here feels really hacky
       if (isConst && node is NewExpression && node.dynamic.isConst) {
         return _invokeConstConstructor(node, code, target, args);
       } else {
         return new Value(target.type, code, node.span);
       }
     }
@@ skipping 676 matching lines @@
   }
 
   void forEach(void f(Member member)) {
     factories.forEach((_, Map constructors) {
       constructors.forEach((_, Member member) {
         f(member);
       });
     });
   }
 }