Use map syntax to clean up null handling in toJson functions (google#1443)

Author: kevmoo

_test_yaml/test/src/build_config.g.dart

@@ -10,8 +10,12 @@ import 'package:test/test.dart';
 
 void main() {
   test('JsonSerializable', () {
-    final person = Person('Inigo', 'Montoya', DateTime(1560, 5, 5))
-      ..orders = [Order(DateTime.now())..item = (Item()..count = 42)];
+    final person = Person(
+      'Inigo',
+      'Montoya',
+      DateTime(1560, 5, 5),
+      middleName: 'Bob',
+    )..orders = [Order(DateTime.now())..item = (Item()..count = 42)];
 
     final personJson = loudEncode(person);
 

example/lib/example.g.dart

@@ -1,5 +1,6 @@
-## 6.8.1-wip
+## 6.9.0-wip
 
+- Use conditional map syntax to clean up `null` handling in `toJson` functions.
 - Require Dart 3.5
 
 ## 6.8.0

example/test/example_test.dart

@@ -5,8 +5,7 @@
 /// Name used for closure argument when generating calls to `map`.
 const closureArg = 'e';
 
-const generatedLocalVarName = 'val';
-const toJsonMapHelperName = 'writeNotNull';
+const generatedLocalVarName = 'value';
 
 const converterOrKeyInstructions = r'''
 * Use `JsonConverter`

json_serializable/CHANGELOG.md

@@ -97,18 +97,22 @@ mixin EncodeHelper implements HelperCore {
 
     if (config.genericArgumentFactories) _writeGenericArgumentFactories(buffer);
 
-    buffer.write(') ');
+    buffer
+      ..write(') ')
+      ..writeln('=> <String, dynamic>{')
+      ..writeAll(accessibleFields.map((field) {
+        final access = _fieldAccess(field);
 
-    final canWriteAllJsonValuesWithoutNullCheck =
-        accessibleFields.every(_canWriteJsonWithoutNullCheck);
+        final keyExpression = safeNameAccess(field);
+        final valueExpression = _serializeField(field, access);
 
-    if (canWriteAllJsonValuesWithoutNullCheck) {
-      // write simple `toJson` method that includes all keys...
-      _writeToJsonSimple(buffer, accessibleFields);
-    } else {
-      // At least one field should be excluded if null
-      _writeToJsonWithNullChecks(buffer, accessibleFields);
-    }
+        final keyValuePair = _canWriteJsonWithoutNullCheck(field)
+            ? '$keyExpression: $valueExpression'
+            : 'if ($valueExpression case final $generatedLocalVarName?) '
+                '$keyExpression: $generatedLocalVarName';
+        return '        $keyValuePair,\n';
+      }))
+      ..writeln('};');
 
     yield buffer.toString();
   }
@@ -125,81 +129,8 @@ mixin EncodeHelper implements HelperCore {
     }
   }
 
-  void _writeToJsonSimple(StringBuffer buffer, Iterable<FieldElement> fields) {
-    buffer
-      ..writeln('=> <String, dynamic>{')
-      ..writeAll(fields.map((field) {
-        final access = _fieldAccess(field);
-        final value =
-            '${safeNameAccess(field)}: ${_serializeField(field, access)}';
-        return '        $value,\n';
-      }))
-      ..writeln('};');
-  }
-
   static const _toJsonParamName = 'instance';
 
-  void _writeToJsonWithNullChecks(
-    StringBuffer buffer,
-    Iterable<FieldElement> fields,
-  ) {
-    buffer
-      ..writeln('{')
-      ..writeln('    final $generatedLocalVarName = <String, dynamic>{');
-
-    // Note that the map literal is left open above. As long as target fields
-    // don't need to be intercepted by the `only if null` logic, write them
-    // to the map literal directly. In theory, should allow more efficient
-    // serialization.
-    var directWrite = true;
-
-    for (final field in fields) {
-      var safeFieldAccess = _fieldAccess(field);
-      final safeJsonKeyString = safeNameAccess(field);
-
-      // If `fieldName` collides with one of the local helpers, prefix
-      // access with `this.`.
-      if (safeFieldAccess == generatedLocalVarName ||
-          safeFieldAccess == toJsonMapHelperName) {
-        safeFieldAccess = 'this.$safeFieldAccess';
-      }
-
-      final expression = _serializeField(field, safeFieldAccess);
-      if (_canWriteJsonWithoutNullCheck(field)) {
-        if (directWrite) {
-          buffer.writeln('      $safeJsonKeyString: $expression,');
-        } else {
-          buffer.writeln(
-              '    $generatedLocalVarName[$safeJsonKeyString] = $expression;');
-        }
-      } else {
-        if (directWrite) {
-          // close the still-open map literal
-          buffer
-            ..writeln('    };')
-            ..writeln()
-
-            // write the helper to be used by all following null-excluding
-            // fields
-            ..writeln('''
-    void $toJsonMapHelperName(String key, dynamic value) {
-      if (value != null) {
-        $generatedLocalVarName[key] = value;
-      }
-    }
-''');
-          directWrite = false;
-        }
-        buffer.writeln(
-            '    $toJsonMapHelperName($safeJsonKeyString, $expression);');
-      }
-    }
-
-    buffer
-      ..writeln('    return $generatedLocalVarName;')
-      ..writeln('  }');
-  }
-
   String _serializeField(FieldElement field, String accessExpression) {
     try {
       return getHelperContext(field)

json_serializable/lib/src/constants.dart

@@ -1,5 +1,5 @@
 name: json_serializable
-version: 6.8.1-wip
+version: 6.9.0-wip
 description: >-
   Automatically generate code for converting to and from JSON by annotating
   Dart classes.

json_serializable/lib/src/encoder_helper.dart

@@ -214,7 +214,6 @@ Map<String, dynamic> _$TrivialNestedNonNullableToJson(
     test('some', () async {
       final output = await runForElementNamed('IncludeIfNullAll');
       expect(output, isNot(contains(generatedLocalVarName)));
-      expect(output, isNot(contains(toJsonMapHelperName)));
     });
   });
 }