Add generic types for strong mode

lib/src/protobuf/extension_field_set.dart

 // Copyright (c) 2015, 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.
 
 part of protobuf;
 
 class _ExtensionFieldSet {
   final _FieldSet _parent;
   final Map<int, Extension> _info = <int, Extension>{};
   final Map<int, dynamic> _values = <int, dynamic>{};
@@ skipping 20 matching lines @@
     var value = _values[tagNumber];
     if (value == null) return false;
     if (value is List) return value.isNotEmpty;
     return true;
   }
 
   /// Ensures that the list exists and an extension is present.
   ///
   /// If it doesn't exist, creates the list and saves the extension.
   /// Suitable for public API and decoders.
-  List _ensureRepeatedField(Extension fi) {
+  List/*<T>*/ _ensureRepeatedField/*<T>*/(Extension/*<T>*/ fi) {
     assert(fi.isRepeated);
     assert(fi.extendee == _parent._messageName);
 
     var list = _values[fi.tagNumber];
-    if (list != null) return list;
+    if (list != null) return list as List/*<T>*/;

[Leaf, 2016/04/01 17:09:56]

Is this going to have the right dynamic type (and hence work in DDC), or is it
going to be List<dynamic>?

[skybrian, 2016/04/01 18:01:40]

It's not statically checkable but the intent is that it always has the right
type. (The list should always be created by fi._createRepeatedField, below, and
the FieldInfo object should have been created with the right dynamic type.)

I'd be happier if I had a way to test this, though.

[skybrian, 2016/04/01 18:04:35]

On second thought, maybe this doesn't work? I'm returning a PbList<T> in place
of a List<T>. Will the "as" check succeed?

[Leaf, 2016/04/01 18:15:59]

If PbList<T> implements or extends List<T>, then yes.

 
     // Add info and create list.
     _validateInfo(fi);
-    list = _parent._message.createRepeatedField(fi.tagNumber, fi);
+    var newList = fi._createRepeatedField(_parent._message);
     _addInfoUnchecked(fi);
-    _setFieldUnchecked(fi, list);
-    return list;
+    _setFieldUnchecked(fi, newList);
+    return newList;
   }
 
   _getFieldOrNull(Extension extension) => _values[extension.tagNumber];
 
   void _clearFieldAndInfo(Extension fi) {
     _clearField(fi);
     _info.remove(fi.tagNumber);
   }
 
   void _clearField(Extension fi) {
@@ skipping 55 matching lines @@
   Iterable<int> get _tagNumbers => _values.keys;
   Iterable<Extension> get _infos => _info.values;
 
   get _hasValues => _values.isNotEmpty;
 
   bool _equalValues(_ExtensionFieldSet other) =>
       _areMapsEqual(_values, other._values);
 
   void _clearValues() => _values.clear();
 }