add conversion of non-string keys for maps

json_serializable_e2e_test/lib/src/model/ilist_model.dart

@@ -9,7 +9,8 @@ class IListWrapper {
 
   IListWrapper(this.iList);
 
-  factory IListWrapper.fromJson(Map<String, dynamic> json) => _$IListWrapperFromJson(json);
+  factory IListWrapper.fromJson(Map<String, dynamic> json) =>
+      _$IListWrapperFromJson(json);
 
   Map<String, dynamic> toJson() => _$IListWrapperToJson(this);
 }
@@ -20,18 +21,32 @@ class IMapWrapper {
 
   IMapWrapper(this.iMap);
 
-  factory IMapWrapper.fromJson(Map<String, dynamic> json) => _$IMapWrapperFromJson(json);
+  factory IMapWrapper.fromJson(Map<String, dynamic> json) =>
+      _$IMapWrapperFromJson(json);
 
   Map<String, dynamic> toJson() => _$IMapWrapperToJson(this);
 }
 
+@JsonSerializable()
+class IMapWrapper2 {
+  final IMap<int, String> iMap;
+
+  IMapWrapper2(this.iMap);
+
+  factory IMapWrapper2.fromJson(Map<String, dynamic> json) =>
+      _$IMapWrapper2FromJson(json);
+
+  Map<String, dynamic> toJson() => _$IMapWrapper2ToJson(this);
+}
+
 @JsonSerializable()
 class ISetWrapper {
   final ISet<String> iSet;
 
   ISetWrapper(this.iSet);
 
-  factory ISetWrapper.fromJson(Map<String, dynamic> json) => _$ISetWrapperFromJson(json);
+  factory ISetWrapper.fromJson(Map<String, dynamic> json) =>
+      _$ISetWrapperFromJson(json);
 
   Map<String, dynamic> toJson() => _$ISetWrapperToJson(this);
 }

json_serializable_e2e_test/test/ilist_test.dart

@@ -1,3 +1,5 @@
+import 'dart:convert';
+
 import 'package:fast_immutable_collections/fast_immutable_collections.dart';
 import 'package:json_serializable_e2e_test/src/model/ilist_model.dart';
 import 'package:test/test.dart';
@@ -54,6 +56,13 @@ void main() {
               'c': 'd',
             }
           });
+      expect(
+          jsonEncode(IMapWrapper2({
+            1: 'b',
+            2: 'd',
+          }.lock)
+              .toJson()),
+          '''{"iMap":{"1":"b","2":"d"}}''');
     });
 
     test('can deserialize IMap', () {
@@ -68,6 +77,14 @@ void main() {
             'a': 'b',
             'c': 'd',
           }));
+          expect(
+          IMapWrapper2.fromJson(jsonDecode(
+            '''{"iMap":{"1":"b","2":"d"}}'''
+          )).iMap,
+          IMap({
+            1: 'b',
+            2: 'd',
+          }));
     });
   });
 }

lib/src/imap/imap.dart

@@ -413,12 +413,13 @@ abstract class IMap<K, V> // ignore: must_be_immutable
     K Function(Object?) fromJsonK,
     V Function(Object?) fromJsonV,
   ) =>
-      json.map<K, V>((key, value) => MapEntry(fromJsonK(key), fromJsonV(value))).lock;
+      json.map<K, V>((key, value) => MapEntry(fromJsonK(_safeKeyFromJson<K>(key)), fromJsonV(value))).lock;
 
   /// Converts to JSon. Json serialization support for json_serializable with @JsonSerializable.
-  Object toJson(Object? Function(K) toJsonK, Object? Function(V) toJsonV) =>
-      unlock.map((key, value) => MapEntry(toJsonK(key), toJsonV(value)));
+  Object toJson<NewK extends Object?>(NewK Function(K) toJsonK, Object? Function(V) toJsonV) =>
+      unlock.map((key, value) => MapEntry(_safeKeyToJson(toJsonK(key)), toJsonV(value)));
 
+
   /// See also: [ImmutableCollection], [ImmutableCollection.lockConfig],
   /// [ImmutableCollection.isConfigLocked],[flushFactor], [defaultConfig]
   static void resetAllConfigurations() {
@@ -1382,3 +1383,52 @@ class InternalsForTestingPurposesIMap {
 }
 
 // /////////////////////////////////////////////////////////////////////////////
+
+Object _safeKeyToJson<NewK extends Object?>(NewK key) {
+  if (key == null){
+    return '$key';
+  }
+  if (key is String) {
+    return key;
+  }
+  if (key is num || key is bool || key is DateTime || key is BigInt || key is Uri){
+    return '$key';
+  }
+  throw Exception('IMap key $key of type ${key.runtimeType} not serializable to/from json');
+}
+
+
+NewK _safeKeyFromJson<NewK extends Object?>(String key) {
+  if (key == 'null'){
+    return null as NewK;
+  }
+  if (_dummyBool is NewK){
+    return (key == 'true') as NewK;
+  }
+  if (_dummyDouble is NewK){
+    return double.parse(key) as NewK;
+  }
+  if (_dummyInt is NewK){
+    return int.parse(key) as NewK;
+  }
+  if (_dummyBigInt is NewK){
+    return BigInt.parse(key) as NewK;
+  }
+  if (_dummyDate is NewK){
+    return DateTime.parse(key) as NewK;
+  }
+  if (_dummyUri is NewK){
+    return Uri.parse(key) as NewK;
+  }
+  if (_dummyString is NewK){
+    return key as NewK;
+  }
+  return key as NewK;
+}
+const _dummyInt = 1;
+const _dummyDouble = 1.0;
+const _dummyString = '';
+const _dummyBool = true;
+final _dummyUri = Uri.parse('http://www.google.com');
+final _dummyDate = DateTime.now();
+final _dummyBigInt = BigInt.from(1);