fix(windows): carry the requested URL on creation failures

flutter_inappwebview/lib/src/in_app_webview/in_app_webview.dart

@@ -479,6 +479,7 @@ class InAppWebView extends StatefulWidget {
   }) : this.fromPlatformCreationParams(
          key: key,
          params: PlatformInAppWebViewWidgetCreationParams(
+           key: key,
            controllerFromPlatform:
                (PlatformInAppWebViewController controller) =>
                    InAppWebViewController.fromPlatform(platform: controller),

flutter_inappwebview_windows/lib/src/in_app_webview/custom_platform_view.dart

@@ -117,6 +117,20 @@ class CustomFlutterViewControllerValue {
   CustomFlutterViewControllerValue.uninitialized() : this(isInitialized: false);
 }
 
+/// The URL a creation request was going to load, read back from its creation
+/// params. It is the only identifier both sides share before the webview
+/// exists, so it is what lets a host match a failure to its own request.
+String? _requestedUrlOf(dynamic arguments) {
+  if (arguments is! Map) return null;
+  final urlRequest = arguments['initialUrlRequest'];
+  if (urlRequest is Map) {
+    final url = urlRequest['url'];
+    if (url != null) return url.toString();
+  }
+  final file = arguments['initialFile'];
+  return file?.toString();
+}
+
 /// Controls a WebView and provides streams for various change events.
 class CustomPlatformViewController
     extends ValueNotifier<CustomFlutterViewControllerValue> {
@@ -142,6 +156,7 @@ class CustomPlatformViewController
   /// Initializes the underlying platform view.
   Future<void> initialize({
     Function(int id)? onPlatformViewCreated,
+    Key? creationKey,
     dynamic arguments,
   }) async {
     if (_isDisposed) {
@@ -158,7 +173,13 @@ class CustomPlatformViewController
       if (!_creatingCompleter.isCompleted) {
         _creatingCompleter.complete();
       }
-      WindowsWebViewCreationFailures.report(error, stackTrace);
+      final failure = WindowsWebViewCreationFailure(
+        error,
+        stackTrace,
+        requestedUrl: _requestedUrlOf(arguments),
+        creationKey: creationKey,
+      );
+      WindowsWebViewCreationFailures.reportFailure(failure);
       rethrow;
     }
 
@@ -330,9 +351,17 @@ class CustomPlatformView extends StatefulWidget {
 
   final Function(int id)? onPlatformViewCreated;
 
+  /// The caller-supplied key that identifies this creation attempt.
+  ///
+  /// It is carried on [WindowsWebViewCreationFailure] so listeners on the
+  /// global failure stream can identify the failed widget even when multiple
+  /// WebViews request the same URL.
+  final Key? creationKey;
+
   const CustomPlatformView({
     this.creationParams,
     this.onPlatformViewCreated,
+    this.creationKey,
     this.scaleFactor,
     this.filterQuality = FilterQuality.none,
   });
@@ -405,6 +434,7 @@ class _CustomPlatformViewState extends State<CustomPlatformView>
             widget.onPlatformViewCreated?.call(id);
             setState(() {});
           },
+          creationKey: widget.creationKey,
           arguments: widget.creationParams,
         )
         .ignore();

flutter_inappwebview_windows/lib/src/in_app_webview/in_app_webview.dart

@@ -330,6 +330,7 @@ class WindowsInAppWebViewWidget extends PlatformInAppWebViewWidget {
 
     return CustomPlatformView(
       onPlatformViewCreated: _onPlatformViewCreated,
+      creationKey: params.key,
       creationParams: <String, dynamic>{
         'initialUrlRequest': params.initialUrlRequest?.toMap(),
         'initialFile': params.initialFile,

flutter_inappwebview_windows/lib/src/in_app_webview/webview_creation_failure.dart

@@ -1,5 +1,7 @@
 import 'dart:async';
 
+import 'package:flutter/widgets.dart';
+
 /// A native WebView creation failure, as reported by the Windows plugin.
 class WindowsWebViewCreationFailure {
   /// The error thrown by the `createInAppWebView` platform call. On Windows it
@@ -8,10 +10,29 @@ class WindowsWebViewCreationFailure {
 
   final StackTrace stackTrace;
 
-  const WindowsWebViewCreationFailure(this.error, this.stackTrace);
+  /// The URL (or file path) the failed webview was asked to load, taken from
+  /// its creation params. Hosts use it to tell whose creation failed: several
+  /// webviews can be created concurrently and this stream is global.
+  final String? requestedUrl;
+
+  /// The [InAppWebView] key for the failed creation attempt.
+  ///
+  /// URLs are not unique: multiple WebViews can create the same URL at once.
+  /// Use this field to match a failure to the right widget. Supply a distinct
+  /// key to each concurrently-created WebView.
+  final Key? creationKey;
+
+  const WindowsWebViewCreationFailure(
+    this.error,
+    this.stackTrace, {
+    this.requestedUrl,
+    this.creationKey,
+  });
 
   @override
-  String toString() => 'WindowsWebViewCreationFailure($error)';
+  String toString() =>
+      'WindowsWebViewCreationFailure('
+      '$error, requestedUrl: $requestedUrl, creationKey: $creationKey)';
 }
 
 /// Broadcasts native WebView creation failures to the host application.
@@ -27,9 +48,25 @@ class WindowsWebViewCreationFailures {
 
   static Stream<WindowsWebViewCreationFailure> get stream => _controller.stream;
 
-  static void report(Object error, StackTrace stackTrace) {
+  static void report(
+    Object error,
+    StackTrace stackTrace, {
+    String? requestedUrl,
+    Key? creationKey,
+  }) {
+    reportFailure(
+      WindowsWebViewCreationFailure(
+        error,
+        stackTrace,
+        requestedUrl: requestedUrl,
+        creationKey: creationKey,
+      ),
+    );
+  }
+
+  static void reportFailure(WindowsWebViewCreationFailure failure) {
     if (_controller.hasListener) {
-      _controller.add(WindowsWebViewCreationFailure(error, stackTrace));
+      _controller.add(failure);
     }
   }
 }

flutter_inappwebview_windows/test/custom_platform_view_creation_failure_test.dart

@@ -205,4 +205,58 @@ void main() {
       expect(tester.takeException(), isNull);
     },
   );
+
+  testWidgets('creation failures carry the failed widget key', (tester) async {
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockMethodCallHandler(IN_APP_WEBVIEW_STATIC_CHANNEL, (call) async {
+          pluginChannelCalls.add(call);
+          final arguments = call.arguments! as Map<dynamic, dynamic>;
+          if (arguments['creation'] == 'fails') {
+            throw PlatformException(code: '0', message: 'creation failed');
+          }
+          return 1;
+        });
+    final failures = <WindowsWebViewCreationFailure>[];
+    final subscription = WindowsWebViewCreationFailures.stream.listen(
+      failures.add,
+    );
+    addTearDown(subscription.cancel);
+    const failedKey = ValueKey<String>('failed');
+    const succeededKey = ValueKey<String>('succeeded');
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Row(
+          children: [
+            Expanded(
+              child: CustomPlatformView(
+                creationKey: failedKey,
+                creationParams: const {
+                  'creation': 'fails',
+                  'initialUrlRequest': {'url': 'file:///plugins/a/index.html'},
+                },
+              ),
+            ),
+            Expanded(
+              child: CustomPlatformView(
+                creationKey: succeededKey,
+                creationParams: const {
+                  'creation': 'succeeds',
+                  'initialUrlRequest': {'url': 'file:///plugins/a/index.html'},
+                },
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+    await tester.pump();
+    await tester.pump();
+
+    expect(failures, hasLength(1));
+    expect(failures.single.requestedUrl, 'file:///plugins/a/index.html');
+    expect(failures.single.creationKey, failedKey);
+    expect(tester.takeException(), isNull);
+  });
 }

flutter_inappwebview_windows/test/webview_creation_failure_test.dart

@@ -15,6 +15,22 @@ void main() {
     expect(received.single.error, same(error));
   });
 
+  test('the requested URL is carried so hosts can tell whose creation failed',
+      () async {
+    final received = <WindowsWebViewCreationFailure>[];
+    final sub = WindowsWebViewCreationFailures.stream.listen(received.add);
+    addTearDown(sub.cancel);
+
+    WindowsWebViewCreationFailures.report(
+      Exception('boom'),
+      StackTrace.current,
+      requestedUrl: 'file:///plugins/a/index.html',
+    );
+    await Future<void>.delayed(Duration.zero);
+
+    expect(received.single.requestedUrl, 'file:///plugins/a/index.html');
+  });
+
   test('reporting without listeners does not throw', () {
     expect(
       () => WindowsWebViewCreationFailures.report(