Add size to Map class

ruby/ext/google/protobuf_c/map.c

@@ -680,6 +680,7 @@ void Map_register(VALUE module) {
   rb_define_method(klass, "delete", Map_delete, 1);
   rb_define_method(klass, "clear", Map_clear, 0);
   rb_define_method(klass, "length", Map_length, 0);
+  rb_define_method(klass, "size", Map_length, 0);
   rb_define_method(klass, "dup", Map_dup, 0);
   rb_define_method(klass, "==", Map_eq, 1);
   rb_define_method(klass, "freeze", Map_freeze, 0);

ruby/src/main/java/com/google/protobuf/jruby/RubyMap.java

@@ -332,7 +332,7 @@ public IRubyObject hasKey(ThreadContext context, IRubyObject key) {
      *
      * Returns the number of entries (key-value pairs) in the map.
      */
-    @JRubyMethod
+    @JRubyMethod(name = {"length", "size"})
     public IRubyObject length(ThreadContext context) {
         return context.runtime.newFixnum(this.table.size());
     }

ruby/tests/basic.rb

@@ -620,5 +620,21 @@ def test_map_freeze
       assert_raise(FrozenErrorType) { m.map_string_int32.delete('a') }
       assert_raise(FrozenErrorType) { m.map_string_int32.clear }
     end
+
+    def test_map_length
+      m = proto_module::MapMessage.new
+      assert_equal 0, m.map_string_int32.length
+      assert_equal 0, m.map_string_msg.length
+      assert_equal 0, m.map_string_int32.size
+      assert_equal 0, m.map_string_msg.size
+
+      m.map_string_int32['a'] = 1
+      m.map_string_int32['b'] = 2
+      m.map_string_msg['a'] = proto_module::TestMessage2.new
+      assert_equal 2, m.map_string_int32.length
+      assert_equal 1, m.map_string_msg.length
+      assert_equal 2, m.map_string_int32.size
+      assert_equal 1, m.map_string_msg.size
+    end
   end
 end