SERVER-28985 Change IDL serialization contract for objects

2 files changed, 22 insertions, 8 deletions

diff --git a/buildscripts/idl/idl/cpp_types.py b/buildscripts/idl/idl/cpp_types.py
index f1ef9ec2f9e..0673ef5e683 100644
--- a/buildscripts/idl/idl/cpp_types.py
+++ b/buildscripts/idl/idl/cpp_types.py
@@ -497,11 +497,14 @@ class _ObjectBsonCppTypeBase(BsonCppTypeBase):
 
     def has_serializer(self):
         # type: () -> bool
-        return False
+        return self._field.serializer is not None
 
     def gen_serializer_expression(self, indented_writer, expression):
         # type: (writer.IndentedTextWriter, unicode) -> unicode
-        raise NotImplementedError()
+        indented_writer.write_line(
+            common.template_args(
+                'const BSONObj localObject = ${expression}.serialize();', expression=expression))
+        return "localObject"
 
 
 # For some fields, we want to support custom serialization but defer most of the serialization to
diff --git a/buildscripts/idl/idl/generator.py b/buildscripts/idl/idl/generator.py
index 19f3b5f783b..bd4a7d30594 100644
--- a/buildscripts/idl/idl/generator.py
+++ b/buildscripts/idl/idl/generator.py
@@ -576,6 +576,23 @@ class _CppSourceFileWriter(_CppFileWriterBase):
                     template_params['expression'] = expression
                     self._writer.write_template('builder->append("${field_name}", ${expression});')
 
+            elif field.bson_serialization_type[0] == 'any':
+                # Any types are special
+                # Array variants - we pass an array builder
+                # Non-array variants - we pass the field name they should use, and a BSONObjBuilder.
+                method_name = writer.get_method_name(field.serializer)
+                template_params['method_name'] = method_name
+
+                if field.array:
+                    self._writer.write_template(
+                        'BSONArrayBuilder arrayBuilder(builder->subarrayStart("${field_name}"));')
+                    with self._block('for (const auto& item : ${access_member}) {', '}'):
+                        # Call a method like class::method(BSONArrayBuilder*)
+                        self._writer.write_template('item.${method_name}(&arrayBuilder);')
+                else:
+                    # Call a method like class::method(StringData, BSONObjBuilder*)
+                    self._writer.write_template(
+                        '${access_member}.${method_name}("${field_name}", builder);')
             else:
                 method_name = writer.get_method_name(field.serializer)
                 template_params['method_name'] = method_name
@@ -643,12 +660,6 @@ class _CppSourceFileWriter(_CppFileWriterBase):
                 with self._block(optional_block_start, '}'):
 
                     if not field.struct_type:
-                        # Is this a scalar bson C++ type?
-                        bson_cpp_type = cpp_types.get_bson_cpp_type(field)
-
-                        needs_custom_serializer = field.serializer or (
-                            bson_cpp_type and bson_cpp_type.has_serializer())
-
                         if needs_custom_serializer:
                             self._gen_serializer_method_custom(field)
                         else: