[web] Better way to detect CanvasKit variant

lib/web_ui/lib/src/engine/browser_detection.dart

@@ -268,6 +268,4 @@ int _detectWebGLVersion() {
 }
 
 /// Whether the current browser supports the Chromium variant of CanvasKit.
-const bool browserSupportsCanvaskitChromium = false;
-// TODO(mdebbar): Uncomment this to enable real detection of browser support.
-// final bool browserSupportsCanvaskitChromium = domIntl.v8BreakIterator != null;
+final bool browserSupportsCanvaskitChromium = domIntl.v8BreakIterator != null;

lib/web_ui/lib/src/engine/canvaskit/canvaskit_api.dart

@@ -28,21 +28,9 @@ import 'renderer.dart';
 /// Entrypoint into the CanvasKit API.
 late CanvasKit canvasKit;
 
-late CanvasKitVariant _canvasKitVariant;
-
-/// Which variant of CanvasKit we are using.
-CanvasKitVariant get canvasKitVariant => _canvasKitVariant;
-set canvasKitVariant(CanvasKitVariant value) {
-  if (value == CanvasKitVariant.auto) {
-    throw ArgumentError.value(
-      value,
-      'value',
-      'CanvasKitVariant.auto is not a valid value for canvasKitVariant',
-    );
-  }
-  _canvasKitVariant = value;
-}
-
+// TODO(mdebbar): Turn this on when CanvasKit Chromium is ready.
+// https://github.com/flutter/flutter/issues/122329
+const bool _enableCanvasKitChromiumInAutoMode = false;
 
 /// Sets the [CanvasKit] object on `window` so we can use `@JS()` to bind to
 /// static APIs.
@@ -1884,6 +1872,13 @@ extension SkParagraphBuilderNamespaceExtension on SkParagraphBuilderNamespace {
     SkParagraphStyle paragraphStyle,
     TypefaceFontProvider? fontManager,
   );
+
+  bool RequiresClientICU() {
+    if (!js_util.hasProperty(this, 'RequiresClientICU')) {
+      return false;
+    }
+    return js_util.callMethod(this, 'RequiresClientICU', const <Object>[],) as bool;
+  }
 }
 
 @JS()
@@ -2699,47 +2694,26 @@ void patchCanvasKitModule(DomHTMLScriptElement canvasKitScript) {
   }
 }
 
-String get _canvasKitBaseUrl => configuration.canvasKitBaseUrl;
-
 const String _kFullCanvasKitJsFileName = 'canvaskit.js';
 const String _kChromiumCanvasKitJsFileName = 'chromium/canvaskit.js';
 
-// TODO(mdebbar): Replace this with a Record once it's supported in Dart.
-class _CanvasKitVariantUrl {
-  const _CanvasKitVariantUrl(this.url, this.variant)
-      : assert(
-          variant != CanvasKitVariant.auto,
-          'CanvasKitVariant.auto cannot have a url',
-        );
-
-  final String url;
-  final CanvasKitVariant variant;
-
-  static _CanvasKitVariantUrl chromium = _CanvasKitVariantUrl(
-    '$_canvasKitBaseUrl$_kChromiumCanvasKitJsFileName',
-    CanvasKitVariant.chromium,
-  );
-
-  static _CanvasKitVariantUrl full = _CanvasKitVariantUrl(
-    '$_canvasKitBaseUrl$_kFullCanvasKitJsFileName',
-    CanvasKitVariant.full,
-  );
-}
-
-List<_CanvasKitVariantUrl> get _canvasKitUrls {
+String get _canvasKitBaseUrl => configuration.canvasKitBaseUrl;
+List<String> get _canvasKitJsFileNames {
   switch (configuration.canvasKitVariant) {
     case CanvasKitVariant.auto:
-      return <_CanvasKitVariantUrl>[
-        if (browserSupportsCanvaskitChromium) _CanvasKitVariantUrl.chromium,
-        _CanvasKitVariantUrl.full,
+      return <String>[
+        if (_enableCanvasKitChromiumInAutoMode) _kChromiumCanvasKitJsFileName,
+        _kFullCanvasKitJsFileName,
       ];
     case CanvasKitVariant.full:
-      return <_CanvasKitVariantUrl>[_CanvasKitVariantUrl.full];
+      return <String>[_kFullCanvasKitJsFileName];
     case CanvasKitVariant.chromium:
-      return <_CanvasKitVariantUrl>[_CanvasKitVariantUrl.chromium];
+      return <String>[_kChromiumCanvasKitJsFileName];
   }
 }
-
+Iterable<String> get _canvasKitJsUrls {
+  return _canvasKitJsFileNames.map((String filename) => '$_canvasKitBaseUrl$filename');
+}
 @visibleForTesting
 String canvasKitWasmModuleUrl(String file, String canvasKitBase) =>
     canvasKitBase + file;
@@ -2749,23 +2723,29 @@ String canvasKitWasmModuleUrl(String file, String canvasKitBase) =>
 /// Downloads the CanvasKit JavaScript, then calls `CanvasKitInit` to download
 /// and intialize the CanvasKit wasm.
 Future<CanvasKit> downloadCanvasKit() async {
-  await _downloadOneOf(_canvasKitUrls);
+  await _downloadOneOf(_canvasKitJsUrls);
 
-  return CanvasKitInit(CanvasKitInitOptions(
+  final CanvasKit canvasKit = await CanvasKitInit(CanvasKitInitOptions(
     locateFile: allowInterop(canvasKitWasmModuleUrl),
   ));
+
+  if (canvasKit.ParagraphBuilder.RequiresClientICU() && !browserSupportsCanvaskitChromium) {
+    throw Exception(
+      'The CanvasKit variant you are using only works on Chromium browsers. '
+      'Please use a different CanvasKit variant, or use a Chromium browser.',
+    );
+  }
+
+  return canvasKit;
 }
 
-/// Finds the first entry in [urls] that can be downloaded successfully, and
+/// Finds the first URL in [urls] that can be downloaded successfully, and
 /// downloads it.
 ///
 /// If none of the URLs can be downloaded, throws an [Exception].
-///
-/// Also sets [canvasKitVariant] to the variant of CanvasKit that was downloaded.
-Future<void> _downloadOneOf(Iterable<_CanvasKitVariantUrl> urls) async {
-  for (final _CanvasKitVariantUrl entry in urls) {
-    if (await _downloadCanvasKitJs(entry.url)) {
-      canvasKitVariant = entry.variant;
+Future<void> _downloadOneOf(Iterable<String> urls) async {
+  for (final String url in urls) {
+    if (await _downloadCanvasKitJs(url)) {
       return;
     }
   }

lib/web_ui/lib/src/engine/canvaskit/text.dart

@@ -984,7 +984,7 @@ class CkParagraphBuilder implements ui.ParagraphBuilder {
 
   /// Builds the CkParagraph with the builder and deletes the builder.
   SkParagraph _buildSkParagraph() {
-    if (canvasKitVariant == CanvasKitVariant.chromium) {
+    if (canvasKit.ParagraphBuilder.RequiresClientICU()) {
       injectClientICU(_paragraphBuilder);
     }
     final SkParagraph result = _paragraphBuilder.build();

lib/web_ui/lib/src/engine/canvaskit/text_fragmenter.dart

@@ -7,15 +7,14 @@ import 'dart:typed_data';
 import '../dom.dart';
 import '../text/line_breaker.dart';
 import 'canvaskit_api.dart';
-import 'renderer.dart';
 
 /// Injects required ICU data into the [builder].
 ///
 /// This should only be used with the CanvasKit Chromium variant that's compiled
 /// without ICU data.
 void injectClientICU(SkParagraphBuilder builder) {
   assert(
-    canvasKitVariant == CanvasKitVariant.chromium,
+    canvasKit.ParagraphBuilder.RequiresClientICU(),
     'This method should only be used with the CanvasKit Chromium variant.',
   );
 

lib/web_ui/test/canvaskit/canvaskit_api_test.dart

@@ -1624,7 +1624,7 @@ void _paragraphTests() {
     builder.pushStyle(
         canvasKit.TextStyle(SkTextStyleProperties()..halfLeading = true));
     builder.pop();
-    if (canvasKitVariant == CanvasKitVariant.chromium) {
+    if (canvasKit.ParagraphBuilder.RequiresClientICU()) {
       injectClientICU(builder);
     }
     final SkParagraph paragraph = builder.build();
@@ -1742,7 +1742,7 @@ void _paragraphTests() {
     );
     builder.addText('hello');
 
-    if (canvasKitVariant == CanvasKitVariant.chromium) {
+    if (canvasKit.ParagraphBuilder.RequiresClientICU()) {
       injectClientICU(builder);
     }