Fix issues with protobuf equality comparisons

lib/src/protobuf/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;
 
 final _emptyList = new List.unmodifiable([]);
 
 /// All the data in a GeneratedMessage.
 ///
@@ skipping 289 matching lines @@
           _eventPlugin.beforeClearField(fi);
         }
       }
     }
     if (_values.isNotEmpty) _values.fillRange(0, _values.length, null);
     if (_hasExtensions) _extensions._clearValues();
   }
 
   bool _equals(_FieldSet o) {
     if (_meta != o._meta) return false;
-    if (!_areListsEqual(_values, o._values)) return false;
+    for (var i = 0; i < _values.length; i++) {
+      if (!_equalFieldValues(_values[i], o._values[i])) return false;
+    }
 
     if (!_hasExtensions || !_extensions._hasValues) {
       // Check if other extensions are logically empty.
       // (Don't create them unnecessarily.)
       if (o._hasExtensions && o._extensions._hasValues) {
         return false;
       }
     } else {
       if (!_extensions._equalValues(o._extensions)) return false;
     }
 
     if (_unknownFields == null || _unknownFields.isEmpty) {
       // Check if other unknown fields is logically empty.
       // (Don't create them unnecessarily.)
       if (o._unknownFields != null && o._unknownFields.isNotEmpty) return false;
     } else {
       // Check if the other unknown fields has the same fields.
       if (_unknownFields != o._unknownFields) return false;
     }
 
     return true;
   }
 
+  bool _equalFieldValues(left, right) {
+    if (left != null && right != null) return _deepEquals(left, right);
+
+    var val = left ?? right;
+
+    // Two uninitialized fields are equal.
+    if (val == null) return true;
+
+    // One field is null. We are comparing an initialized field
+    // with its default value.
+
+    // An empty repeated field is the same as uninitialized.
+    // This is because accessing a repeated field automatically creates it.
+    // We don't want reading a field to change equality comparisons.
+    if (val is List && val.isEmpty) return true;
+
+    // For now, initialized and uninitialized fields are different.
+    // TODO(skybrian) consider other cases; should we compare with the
+    // default value or not?
+    return false;
+  }
+
   /// Calculates a hash code based on the contents of the protobuf.
   ///
   /// The hash may change when any field changes (recursively).
   /// Therefore, protobufs used as map keys shouldn't be changed.
   int get _hashCode {
     int hash;
 
     void hashEnumList(PbList enums) {
       enums.forEach((ProtobufEnum enm) {
         hash = (31 * hash + enm.value) & 0x3fffffff;
@@ skipping 167 matching lines @@
   void _appendInvalidFields(List<String> problems, String prefix) {
     if (!_hasRequiredFields) return;
     for (var fi in _infos) {
       var value = _values[fi.index];
       fi._appendInvalidFields(problems, value, prefix);
     }
     // TODO(skybrian): search extensions as well
     // https://github.com/dart-lang/dart-protobuf/issues/46
   }
 }