1 files changed, 21 insertions, 10 deletions

diff --git a/js/map.js b/js/map.js
index d423499f..2fb14837 100644
--- a/js/map.js
+++ b/js/map.js
@@ -48,9 +48,9 @@ goog.forwardDeclare('jspb.BinaryWriter');
  *
  * @template K, V
  *
- * @param {!Array<!Array<!Object>>} arr
+ * @param {!Array<!Array<?>>} arr
  *
- * @param {?function(new:V)|function(new:V,?)=} opt_valueCtor
+ * @param {?function(new:V, ?=)=} opt_valueCtor
  *    The constructor for type V, if type V is a message type.
  *
  * @constructor
@@ -118,7 +118,7 @@ jspb.Map.prototype.toArray = function() {
     strKeys.sort();
     for (var i = 0; i < strKeys.length; i++) {
       var entry = this.map_[strKeys[i]];
-      var valueWrapper = /** @type {!Object} */ (entry.valueWrapper);
+      var valueWrapper = /** @type {?jspb.Message} */ (entry.valueWrapper);
       if (valueWrapper) {
         valueWrapper.toArray();
       }
@@ -165,7 +165,7 @@ jspb.Map.prototype.toObject = function(includeInstance, valueToObject) {
  *
  * @template K, V
  * @param {!Array<!Array<!Object>>} entries
- * @param {!function(new:V)|function(new:V,?)} valueCtor
+ * @param {!function(new:V,?=)} valueCtor
  *    The constructor for type V.
  * @param {!function(!Object):V} valueFromObject
  *    The fromObject function for type V.
@@ -432,7 +432,8 @@ jspb.Map.prototype.serializeBinary = function(
       valueWriterFn.call(writer, 2, this.wrapEntry_(entry),
                          opt_valueWriterCallback);
     } else {
-      valueWriterFn.call(writer, 2, entry.value);
+      /** @type {function(this:jspb.BinaryWriter,number,?)} */ (valueWriterFn)
+          .call(writer, 2, entry.value);
     }
     writer.endSubMessage();
   }
@@ -442,7 +443,8 @@ jspb.Map.prototype.serializeBinary = function(
 /**
  * Read one key/value message from the given BinaryReader. Compatible as the
  * `reader` callback parameter to jspb.BinaryReader.readMessage, to be called
- * when a key/value pair submessage is encountered.
+ * when a key/value pair submessage is encountered. If the Key is undefined,
+ * we should default it to 0.
  * @template K, V
  * @param {!jspb.Map} map
  * @param {!jspb.BinaryReader} reader
@@ -456,12 +458,17 @@ jspb.Map.prototype.serializeBinary = function(
  *    readMessage, in which case the second callback arg form is used.
  *
  * @param {?function(V,!jspb.BinaryReader)=} opt_valueReaderCallback
- *    The BinaryReader parsing callback for type V, if V is a message type.
+ *    The BinaryReader parsing callback for type V, if V is a message type
+ *
+ * @param {K=} opt_defaultKey
+ *    The default value for the type of map keys. Accepting map
+ *    entries with unset keys is required for maps to be backwards compatible
+ *    with the repeated message representation described here: goo.gl/zuoLAC
  *
  */
 jspb.Map.deserializeBinary = function(map, reader, keyReaderFn, valueReaderFn,
-                                      opt_valueReaderCallback) {
-  var key = undefined;
+                                      opt_valueReaderCallback, opt_defaultKey) {
+  var key = opt_defaultKey;
   var value = undefined;
 
   while (reader.nextField()) {
@@ -469,16 +476,20 @@ jspb.Map.deserializeBinary = function(map, reader, keyReaderFn, valueReaderFn,
       break;
     }
     var field = reader.getFieldNumber();
+
     if (field == 1) {
       // Key.
       key = keyReaderFn.call(reader);
     } else if (field == 2) {
       // Value.
       if (map.valueCtor_) {
+        goog.asserts.assert(opt_valueReaderCallback);
         value = new map.valueCtor_();
         valueReaderFn.call(reader, value, opt_valueReaderCallback);
       } else {
-        value = valueReaderFn.call(reader);
+        value =
+            (/** @type {function(this:jspb.BinaryReader):?} */ (valueReaderFn))
+                .call(reader);
       }
     }
   }