Improve toJson generation with some no-write null fields

CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.2.3
+
+* Write out `toJson` methods more efficiently when the first fields written are
+  not intercepted by the null-checking method.
+
 ## 0.2.2+1
 
 * Simplify the serialization of `Map` instances when no conversion is required

lib/src/json_serializable_generator.dart

@@ -151,15 +151,13 @@ class JsonSerializableGenerator
       Map<String, FieldElement> fields, bool includeIfNull) {
     buffer.writeln('{');
 
-    // TODO(kevmoo) We could write all values up to the null-excluded value
-    //   directly in this literal.
-    buffer.writeln('var $toJsonMapVarName = <String, dynamic>{};');
+    buffer.writeln('var $toJsonMapVarName = <String, dynamic>{');
 
-    buffer.writeln('''void $toJsonMapHelperName(String key, dynamic value) {
-    if (value != null) {
-      $toJsonMapVarName[key] = value;
-    }
-    }''');
+    // Note that the map literal is left open above. As long as target fields
+    // don't need to be intercepted by the `only if null` logic, write them
+    // to the map literal directly. In theory, should allow more efficient
+    // serialization.
+    var directWrite = true;
 
     fields.forEach((fieldName, field) {
       try {
@@ -173,9 +171,29 @@ class JsonSerializableGenerator
         }
 
         if (_includeIfNull(field, includeIfNull)) {
-          buffer.writeln('$toJsonMapVarName[$safeJsonKeyString] = '
-              '${_serialize(field.type, fieldName,  _nullable(field))};');
+          if (directWrite) {
+            buffer.writeln('$safeJsonKeyString : '
+                '${_serialize(field.type, fieldName, _nullable(field))},');
+          } else {
+            buffer.writeln('$toJsonMapVarName[$safeJsonKeyString] = '
+                '${_serialize(field.type, fieldName, _nullable(field))};');
+          }
         } else {
+          if (directWrite) {
+            // close the still-open map literal
+            buffer.writeln('};');
+            buffer.writeln();
+
+            // write the helper to be used by all following null-excluding
+            // fields
+            buffer.writeln('''
+void $toJsonMapHelperName(String key, dynamic value) {
+  if (value != null) {
+    $toJsonMapVarName[key] = value;
+  }
+}''');
+            directWrite = false;
+          }
           buffer.writeln('$toJsonMapHelperName($safeJsonKeyString, '
               '${_serialize(field.type, fieldName, _nullable(field))});');
         }
@@ -187,7 +205,7 @@ class JsonSerializableGenerator
       }
     });
 
-    buffer.writeln(r'return $map;');
+    buffer.writeln('return $toJsonMapVarName;');
 
     buffer.writeln('}');
   }

lib/src/utils.dart

@@ -44,5 +44,5 @@ void log(object) {
   stderr.writeln(['***', object, '***'].join('\n'));
 }
 
-final toJsonMapVarName = r'$map';
-final toJsonMapHelperName = r'$writeNotNull';
+final toJsonMapVarName = 'val';
+final toJsonMapHelperName = 'writeNotNull';

pubspec.yaml

@@ -1,5 +1,5 @@
 name: json_serializable
-version: 0.2.2+1
+version: 0.2.3-dev
 author: Dart Team <misc@dartlang.org>
 description: Generates utilities to aid in serializing to/from JSON.
 homepage: https://github.com/dart-lang/json_serializable
@@ -15,4 +15,5 @@ dev_dependencies:
   build_runner: ^0.4.0
   build_test: ^0.6.0
   collection: ^1.14.0
+  dart_style: ^1.0.0
   test: ^0.12.3

test/json_serializable_test.dart

@@ -9,6 +9,7 @@ import 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/src/string_source.dart';
+import 'package:dart_style/dart_style.dart' as dart_style;
 import 'package:json_serializable/generators.dart';
 import 'package:json_serializable/src/utils.dart';
 import 'package:path/path.dart' as p;
@@ -99,21 +100,65 @@ void main() {
   });
 
   group('valid inputs', () {
-    test('class with no fields', () async {
+    test('class with no ctor params', () async {
       var output = await _runForElementNamed('Person');
-
-      expect(output, isNotNull);
-
-      // TODO: test the actual output
-      // print(output);
+      expect(output,
+          r'''Person _$PersonFromJson(Map<String, dynamic> json) => new Person()
+  ..firstName = json['firstName'] as String
+  ..lastName = json['lastName'] as String
+  ..height = json['h'] as int
+  ..dateOfBirth = json['dateOfBirth'] == null
+      ? null
+      : DateTime.parse(json['dateOfBirth'] as String)
+  ..dynamicType = json['dynamicType']
+  ..varType = json['varType']
+  ..listOfInts = (json['listOfInts'] as List)?.map((e) => e as int)?.toList();
+
+abstract class _$PersonSerializerMixin {
+  String get firstName;
+  String get lastName;
+  int get height;
+  DateTime get dateOfBirth;
+  dynamic get dynamicType;
+  dynamic get varType;
+  List<int> get listOfInts;
+  Map<String, dynamic> toJson() => <String, dynamic>{
+        'firstName': firstName,
+        'lastName': lastName,
+        'h': height,
+        'dateOfBirth': dateOfBirth?.toIso8601String(),
+        'dynamicType': dynamicType,
+        'varType': varType,
+        'listOfInts': listOfInts
+      };
+}
+''');
     });
 
     test('class with ctor params', () async {
       var output = await _runForElementNamed('Order');
-      expect(output, isNotNull);
-
-      // TODO: test the actual output
-      // print(output);
+      expect(output,
+          r'''Order _$OrderFromJson(Map<String, dynamic> json) => new Order(
+    json['height'] as int,
+    json['firstName'] as String,
+    json['lastName'] as String)
+  ..dateOfBirth = json['dateOfBirth'] == null
+      ? null
+      : DateTime.parse(json['dateOfBirth'] as String);
+
+abstract class _$OrderSerializerMixin {
+  String get firstName;
+  String get lastName;
+  int get height;
+  DateTime get dateOfBirth;
+  Map<String, dynamic> toJson() => <String, dynamic>{
+        'firstName': firstName,
+        'lastName': lastName,
+        'height': height,
+        'dateOfBirth': dateOfBirth?.toIso8601String()
+      };
+}
+''');
     });
 
     test('class with child json-able object', () async {
@@ -159,20 +204,24 @@ void main() {
 
     test('all', () async {
       var output = await _runForElementNamed('IncludeIfNullOverride');
-      expect(output, contains("$toJsonMapVarName[\'number\'] = number;"));
+      expect(output, contains("'number': number,"));
       expect(output, contains("$toJsonMapHelperName('str', str);"));
     });
   });
 }
 
 const _generator = const JsonSerializableGenerator();
 
+final _formatter = new dart_style.DartFormatter();
+
 Future<String> _runForElementNamed(String name) async {
   var library = new LibraryReader(_compUnit.element.library);
   var element = library.allElements.singleWhere((e) => e.name == name);
   var annotation = _generator.typeChecker.firstAnnotationOf(element);
-  return _generator.generateForAnnotatedElement(
+  var generated = await _generator.generateForAnnotatedElement(
       element, new ConstantReader(annotation), null);
+
+  return _formatter.format(generated);
 }
 
 Future<CompilationUnit> _getCompilationUnitForString(String projectPath) async {

test/kitchen_sink_test.dart

@@ -157,7 +157,7 @@ void _sharedTests(
       ..dateTime = new DateTime.now()
       ..dateTimeList = []
       ..crazyComplex = []
-      ..$map = {};
+      ..val = {};
 
     var json = item.toJson();
     expect(json.keys, orderedEquals(_expectedOrder));

test/test_files/bathtub.dart

@@ -83,9 +83,9 @@ class Bathtub extends Object
 
   // Handle fields with names that collide with helper names
   @JsonKey(nullable: false, includeIfNull: false)
-  Map<String, bool> $map = {};
+  Map<String, bool> val = {};
   @JsonKey(nullable: false)
-  bool $writeNotNull;
+  bool writeNotNull;
   @JsonKey(nullable: false, name: r'$string')
   String string;
 

test/test_files/kitchen_sink.dart

@@ -73,8 +73,8 @@ class KitchenSink extends Object with _$KitchenSinkSerializerMixin {
 
   // Handle fields with names that collide with helper names
   @JsonKey(includeIfNull: false)
-  Map<String, bool> $map;
-  bool $writeNotNull;
+  Map<String, bool> val;
+  bool writeNotNull;
   @JsonKey(name: r'$string')
   String string;