Throw on dupe keys

json_serializable/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.2.5
+
+* Throw an exception if a duplicate JSON key is detected.
+
 ## 0.2.4+1
 
 * Throw a more helpful error when a constructor is missing.

json_serializable/lib/src/json_serializable_generator.dart

@@ -98,7 +98,7 @@ class JsonSerializableGenerator
     // Explicitly using `LinkedHashMap` – we want these ordered.
     var fields = new LinkedHashMap<String, FieldElement>.fromIterable(
         fieldsList,
-        key: (FieldElement f) => f.name);
+        key: (f) => (f as FieldElement).name);
 
     // Get the constructor to use for the factory
 
@@ -116,6 +116,20 @@ class JsonSerializableGenerator
       }
     }
 
+    // Now we check for duplicate JSON keys due to colliding annotations.
+    // We do this now, since we have a final field list after any pruning done
+    // by `createFactory`.
+
+    fields.values.fold(new Set<String>(), (Set<String> set, fe) {
+      var jsonKey = _jsonKeyFor(fe).name ?? fe.name;
+      if (!set.add(jsonKey)) {
+        throw new InvalidGenerationSourceError(
+            'More than one field has the JSON key `$jsonKey`.',
+            todo: 'Check the `JsonKey` annotations on fields.');
+      }
+      return set;
+    });
+
     if (annotation.read('createToJson').boolValue) {
       //
       // Generate the mixin class

json_serializable/test/json_serializable_test.dart

@@ -188,11 +188,29 @@ abstract class _$OrderSerializerMixin {
     });
   });
 
-  test('reads JsonKey annotations', () async {
-    var output = await _runForElementNamed('Person');
+  group('JsonKey', () {
+    test('works to change the name of a field', () async {
+      var output = await _runForElementNamed('Person');
+
+      expect(output, contains("'h': height,"));
+      expect(output, contains("..height = json['h']"));
+    });
 
-    expect(output, contains("'h': height,"));
-    expect(output, contains("..height = json['h']"));
+    test('works to change the name of a field', () async {
+      expect(
+          () => _runForElementNamed('KeyDupesField'),
+          throwsInvalidGenerationSourceError(
+              'More than one field has the JSON key `str`.',
+              'Check the `JsonKey` annotations on fields.'));
+    });
+
+    test('works to change the name of a field', () async {
+      expect(
+          () => _runForElementNamed('DupeKeys'),
+          throwsInvalidGenerationSourceError(
+              'More than one field has the JSON key `a`.',
+              'Check the `JsonKey` annotations on fields.'));
+    });
   });
 
   group('includeIfNull', () {
@@ -366,4 +384,21 @@ class NoCtorClass {
 
   factory TestDoneEvent.fromJson(Map<String, dynamic> json) => null;
 }
+
+@JsonSerializable(createFactory: false)
+class KeyDupesField {
+  @JsonKey(name: 'str')
+  int number;
+
+  String str;
+}
+
+@JsonSerializable(createFactory: false)
+class DupeKeys {
+  @JsonKey(name: 'a')
+  int number;
+
+  @JsonKey(name: 'a')
+  String str;
+}
 ''';