[camera_web] Fixed crashing bug on camera_web 0.3.5 for Safari (#10595)

On certain browsers (Safari), getting `facingMode` on video track capabilities is not supported. The code first checks if `facingMode` is available on `MediaTrackSettings` using `facingModeNullable` but when the code checks for facingMode on `MediaTrackCapabilities`, it uses the non nullable `facingMode` getter instead of `facingModeNullable`. This causes a crash and the camera isn't initialized correctly.

This is a blocker for reliably deploying camera_web 0.3.5 which enables people to use WASM with camera functionality.

Fixes flutter/flutter#155210

## Testing

Tested on Safari on Mac and iPhone with camera initialization - camera now successfully initializes where it previously failed.

## Pre-Review Checklist

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Author: jalen-videotape

packages/camera/camera_web/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.3.5+3
+
+* Fixes camera initialization failure on Safari by fixing a null check operator error using
+  a nullable getter and null safe practices.
+
 ## 0.3.5+2
 
 * Fixes camera initialization failure on Firefox Android by using `{video: true}` instead

packages/camera/camera_web/example/integration_test/camera_service_test.dart

@@ -708,6 +708,29 @@ void main() {
 
           expect(facingMode, isNull);
         });
+
+        testWidgets('returns null '
+            'when the facing mode setting is empty and '
+            'the facingMode capability is null', (WidgetTester tester) async {
+          mockVideoTrack.getSettings = () {
+            return createJSInteropWrapper(FakeMediaTrackSettings())
+                as web.MediaTrackSettings;
+          }.toJS;
+          mockVideoTrack.getCapabilities = () {
+            return createJSInteropWrapper(FakeMediaTrackCapabilities())
+                as web.MediaTrackCapabilities;
+          }.toJS;
+
+          when(
+            jsUtil.hasProperty(videoTrack, 'getCapabilities'.toJS),
+          ).thenReturn(true);
+
+          final String? facingMode = cameraService.getFacingModeForVideoTrack(
+            videoTrack,
+          );
+
+          expect(facingMode, isNull);
+        });
       });
     });
 

packages/camera/camera_web/example/integration_test/helpers/mocks.dart

@@ -284,3 +284,23 @@ class MockEventStreamProvider<T extends web.Event> extends Mock
         as ElementStream<T>;
   }
 }
+
+/// A fake [web.MediaTrackCapabilities] where facingMode is null/undefined.
+///
+/// Used to test null-safe handling when the browser doesn't provide
+/// the facingMode capability.
+@JSExport()
+class FakeMediaTrackCapabilities {
+  // Dummy property required by @JSExport
+  bool get dummy => true;
+}
+
+/// A fake [web.MediaTrackSettings] where facingMode is null/undefined.
+///
+/// Used to test null-safe handling when the browser doesn't provide
+/// the facingMode capability.
+@JSExport()
+class FakeMediaTrackSettings {
+  // Dummy property required by @JSExport
+  bool get dummy => true;
+}

packages/camera/camera_web/lib/src/camera_service.dart

@@ -200,11 +200,11 @@ class CameraService {
 
       // A list of facing mode capabilities as
       // the camera may support multiple facing modes.
-      final List<String> facingModeCapabilities = videoTrackCapabilities
-          .facingMode
-          .toDart
-          .map((JSString e) => e.toDart)
-          .toList();
+      final List<String> facingModeCapabilities =
+          videoTrackCapabilities.facingModeNullable?.toDart
+              .map((JSString e) => e.toDart)
+              .toList() ??
+          <String>[];
 
       if (facingModeCapabilities.isNotEmpty) {
         final String facingModeCapability = facingModeCapabilities.first;

packages/camera/camera_web/lib/src/pkg_web_tweaks.dart

@@ -31,6 +31,9 @@ extension NonStandardFieldsOnMediaTrackCapabilities on MediaTrackCapabilities {
 
   @JS('torch')
   external JSArray<JSBoolean>? get torchNullable;
+
+  @JS('facingMode')
+  external JSArray<JSString>? get facingModeNullable;
 }
 
 /// Adds missing fields to [MediaTrackSettings]

packages/camera/camera_web/pubspec.yaml

@@ -2,7 +2,7 @@ name: camera_web
 description: A Flutter plugin for getting information about and controlling the camera on Web.
 repository: https://github.com/flutter/packages/tree/main/packages/camera/camera_web
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+camera%22
-version: 0.3.5+2
+version: 0.3.5+3
 
 environment:
   sdk: ^3.8.0