JsonKey.fromJson/toJson now support functions with optional arguments.

Author: kevmoo

json_serializable/CHANGELOG.md

@@ -8,9 +8,11 @@
    `_myHelper(json['key'] as Map)` instead of
    `_myHelper(json['key'] as Map<dynamic, dynamic>)`.  
 
+* `JsonKey.fromJson`/`.toJson` now support functions with optional arguments.
+
 ## 0.5.2
 
-* If `fromJson`/`toJson` are set in `JsonKey`, apply them before any custom
+* If `JsonKey.fromJson`/`toJson` are set, apply them before any custom
   or default `TypeHelper` instances. This allows custom `DateTime` parsing,
   by preempting the existing `DateTime` `TypeHelper`.
 

json_serializable/lib/src/json_key_helpers.dart

@@ -96,17 +96,16 @@ ConvertData _getFunctionName(
   }
   var functionElement = type.element as FunctionElement;
 
-  var positionalParams = functionElement.parameters
-      .where((pe) => pe.isPositional)
-      .toList();
-
-  if (positionalParams.length != 1) {
+  if (functionElement.parameters.isEmpty ||
+      functionElement.parameters.first.isNamed ||
+      functionElement.parameters.where((pe) => !pe.isOptional).length > 1) {
     _throwUnsupported(
         element,
         'The `$paramName` function `${functionElement.name}` must have one '
         'positional paramater.');
   }
 
+  var argType = functionElement.parameters.first.type;
   if (isFrom) {
     var returnType = functionElement.returnType;
     if (!returnType.isAssignableTo(element.type)) {
@@ -116,7 +115,6 @@ ConvertData _getFunctionName(
           '`$returnType` is not compatible with field type `${element.type}`.');
     }
   } else {
-    var argType = positionalParams.single.type;
     if (!element.type.isAssignableTo(argType)) {
       _throwUnsupported(
           element,
@@ -125,5 +123,5 @@ ConvertData _getFunctionName(
           ' `${element.type}`.');
     }
   }
-  return new ConvertData._(functionElement.name, positionalParams.single.type);
+  return new ConvertData._(functionElement.name, argType);
 }

json_serializable/test/json_serializable_test.dart

@@ -332,6 +332,18 @@ abstract class _$OrderSerializerMixin {
             'The function provided for `fromJson` must be top-level. '
             'Static class methods (`_staticFunc`) are not supported.');
       });
+      test('BadNoArgs', () {
+        expectThrows('BadNoArgs',
+            'Error with `@JsonKey` on `field`. The `fromJson` function `_noArgs` must have one positional paramater.');
+      });
+      test('BadTwoRequiredPositional', () {
+        expectThrows('BadTwoRequiredPositional',
+            'Error with `@JsonKey` on `field`. The `fromJson` function `_twoArgs` must have one positional paramater.');
+      });
+      test('BadOneNamed', () {
+        expectThrows('BadOneNamed',
+            'Error with `@JsonKey` on `field`. The `fromJson` function `_oneNamed` must have one positional paramater.');
+      });
     });
 
     group('toJsonFunction', () {
@@ -386,6 +398,19 @@ FromDynamicCollection _$FromDynamicCollectionFromJson(
           : _fromDynamicIterable(json['iterableField'] as List);
 ''');
       });
+      test('OkayOneNormalOptionalPositional', () async {
+        var output =
+            await runForElementNamed('OkayOneNormalOptionalPositional');
+        expect(output, contains("_oneNormalOnePositional(json['field'])"));
+      });
+      test('OkayOneNormalOptionalNamed', () async {
+        var output = await runForElementNamed('OkayOneNormalOptionalNamed');
+        expect(output, contains("_oneNormalOptionalNamed(json['field'])"));
+      });
+      test('OkayOnlyOptionalPositional', () async {
+        var output = await runForElementNamed('OkayOnlyOptionalPositional');
+        expect(output, contains("_onlyOptionalPositional(json['field'])"));
+      });
     }
   });
 

json_serializable/test/src/json_serializable_test_input.dart

@@ -296,3 +296,51 @@ class FromDynamicCollection {
   @JsonKey(fromJson: _fromDynamicIterable)
   String iterableField;
 }
+
+String _noArgs() => null;
+
+@JsonSerializable(createToJson: false)
+class BadNoArgs {
+  @JsonKey(fromJson: _noArgs)
+  String field;
+}
+
+String _twoArgs(a, b) => null;
+
+@JsonSerializable(createToJson: false)
+class BadTwoRequiredPositional {
+  @JsonKey(fromJson: _twoArgs)
+  String field;
+}
+
+String _oneNamed({a}) => null;
+
+@JsonSerializable(createToJson: false)
+class BadOneNamed {
+  @JsonKey(fromJson: _oneNamed)
+  String field;
+}
+
+String _oneNormalOnePositional(a, [b]) => null;
+
+@JsonSerializable(createToJson: false)
+class OkayOneNormalOptionalPositional {
+  @JsonKey(fromJson: _oneNormalOnePositional)
+  String field;
+}
+
+String _oneNormalOptionalNamed(a, {b}) => null;
+
+@JsonSerializable(createToJson: false)
+class OkayOneNormalOptionalNamed {
+  @JsonKey(fromJson: _oneNormalOptionalNamed)
+  String field;
+}
+
+String _onlyOptionalPositional([a, b]) => null;
+
+@JsonSerializable(createToJson: false)
+class OkayOnlyOptionalPositional {
+  @JsonKey(fromJson: _onlyOptionalPositional)
+  String field;
+}