Fix the zIndex-related issue in the copyWith method. (#9396)

This assertion fails when using the `copyWith` method.

https://github.com/flutter/packages/blob/007e2f1e468b8e870544c16ce21ad39f97299241/packages/google_maps_flutter/google_maps_flutter_platform_interface/lib/src/types/marker.dart#L165

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: yiiim

packages/google_maps_flutter/google_maps_flutter_platform_interface/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.12.1
+
+* Fixes the `zIndex` issue in the `copyWith` method.
+
 ## 2.12.0
 
 * Deprecates `zIndex` parameter in `Marker` in favor of `zIndexInt`.

packages/google_maps_flutter/google_maps_flutter_platform_interface/lib/src/types/marker.dart

@@ -280,6 +280,8 @@ class Marker implements MapsObject<Marker> {
     ValueChanged<LatLng>? onDragEndParam,
     ClusterManagerId? clusterManagerIdParam,
   }) {
+    assert(zIndexParam == null || zIndexIntParam == null,
+        'Only one of zIndexParam and zIndexIntParam can be provided');
     return Marker(
       markerId: markerId,
       alpha: alphaParam ?? alpha,
@@ -292,8 +294,7 @@ class Marker implements MapsObject<Marker> {
       position: positionParam ?? position,
       rotation: rotationParam ?? rotation,
       visible: visibleParam ?? visible,
-      zIndex: zIndexParam ?? zIndex,
-      zIndexInt: zIndexIntParam ?? zIndexInt,
+      zIndex: zIndexIntParam?.toDouble() ?? zIndexParam ?? zIndex,
       onTap: onTapParam ?? onTap,
       onDragStart: onDragStartParam ?? onDragStart,
       onDrag: onDragParam ?? onDrag,

packages/google_maps_flutter/google_maps_flutter_platform_interface/pubspec.yaml

@@ -4,7 +4,7 @@ repository: https://github.com/flutter/packages/tree/main/packages/google_maps_f
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+maps%22
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 2.12.0
+version: 2.12.1
 
 environment:
   sdk: ^3.6.0

packages/google_maps_flutter/google_maps_flutter_platform_interface/test/types/marker_test.dart

@@ -201,5 +201,25 @@ void main() {
       expect(marker.zIndexInt, 5);
       expect(marker.zIndex, 5.00);
     });
+
+    test('zIndexInt param copyWith', () {
+      const Marker marker = Marker(
+        markerId: MarkerId('ABC123'),
+        zIndexInt: 5,
+      );
+      final Marker copy = marker.copyWith(zIndexIntParam: 10);
+      expect(copy.zIndexInt, 10);
+      expect(copy.zIndex, 10.0);
+    });
+
+    test('zIndex param copyWith', () {
+      const Marker marker = Marker(
+        markerId: MarkerId('ABC123'),
+        zIndexInt: 5,
+      );
+      final Marker copy = marker.copyWith(zIndexParam: 10.0);
+      expect(copy.zIndexInt, 10);
+      expect(copy.zIndex, 10.0);
+    });
   });
 }