From fc8856eb80d306ac40563582a1212a07141d9001 Mon Sep 17 00:00:00 2001
From: Mouad Debbar <mdebbar@google.com>
Date: Fri, 16 Jun 2023 09:53:05 -0400
Subject: [PATCH] [web] Don't crash on `const HtmlElementView()` (#128965)

Previously, when the code contained `const HtmlElementView()` it would break even if it's guarded by `if (kIsWeb)`.

This PR makes it such that `const HtmlElementView()` is allowed but it still throws if it gets inserted into the widget tree by mistake on non-web platforms.

One improvement we can make in the future is to have a conditional import:
- `_html_element_view_web.dart` that contains the real `HtmlElementView` that can only be instantiated on web.
- `_html_element_view_io.dart` that contains a stub with an unimplemented `build()` method.

Fixes https://github.com/flutter/flutter/issues/43532
---
 .../lib/src/widgets/platform_view.dart        |  3 ++-
 .../test/widgets/platform_view_test.dart      | 24 +++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/packages/flutter/lib/src/widgets/platform_view.dart b/packages/flutter/lib/src/widgets/platform_view.dart
index 32ce829a7f..722a22b983 100644
--- a/packages/flutter/lib/src/widgets/platform_view.dart
+++ b/packages/flutter/lib/src/widgets/platform_view.dart
@@ -346,7 +346,7 @@ class HtmlElementView extends StatelessWidget {
     required this.viewType,
     this.onPlatformViewCreated,
     this.creationParams,
-  }) : assert(kIsWeb, 'HtmlElementView is only available on Flutter Web.');
+  });
 
   /// The unique identifier for the HTML view type to be embedded by this widget.
   ///
@@ -363,6 +363,7 @@ class HtmlElementView extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    assert(kIsWeb, 'HtmlElementView is only available on Flutter Web.');
     return PlatformViewLink(
       viewType: viewType,
       onCreatePlatformView: _createHtmlElementView,
diff --git a/packages/flutter/test/widgets/platform_view_test.dart b/packages/flutter/test/widgets/platform_view_test.dart
index 1016909fea..7b4bc72037 100644
--- a/packages/flutter/test/widgets/platform_view_test.dart
+++ b/packages/flutter/test/widgets/platform_view_test.dart
@@ -3168,4 +3168,28 @@ void main() {
     expect(controller.dispatchedPointerEvents, hasLength(1));
     expect(controller.dispatchedPointerEvents[0], isA<PointerHoverEvent>());
   });
+
+  testWidgets('HtmlElementView can be instantiated', (WidgetTester tester) async {
+    late final Widget htmlElementView;
+    expect(() {
+      htmlElementView = const HtmlElementView(viewType: 'webview');
+    }, returnsNormally);
+
+    await tester.pumpWidget(
+      Center(
+        child: SizedBox(
+          width: 100,
+          height: 100,
+          child: htmlElementView,
+        ),
+      )
+    );
+    await tester.pumpAndSettle();
+
+    // This file runs on non-web platforms, so we expect `HtmlElementView` to
+    // fail.
+    final dynamic exception = tester.takeException();
+    expect(exception, isAssertionError);
+    expect(exception.toString(), contains('HtmlElementView is only available on Flutter Web'));
+  });
 }