[web] Cleanup everything HTML from the engine (outside html/ folder) (#162840)

Things being cleaned up:

- Remove `flutter.js` support for HTML/AUTO renderers.
- Delete the renderer auto-detection logic and flag.
- Remove references to the `HtmlRenderer` from renderer-agnostic code.
- Remove the `auto-selected`/`requested explicitly` info from the DOM.

As a follow up to this, I'll create another PR that deletes the entire
`html/` folder.

engine/src/flutter/lib/web_ui/flutter_js/src/loader.js

@@ -92,13 +92,7 @@ export class FlutterLoader {
      * @param {import("./types").WebRenderer} renderer
      **/
     const buildContainsRenderer = (build, renderer) => {
-      switch (build.renderer) {
-        // The "auto" build contains both canvaskit and html renderers.
-        case "auto":
-          return renderer == "canvaskit" || renderer == "html";
-        default:
-          return build.renderer == renderer;
-      }
+      return build.renderer == renderer;
     }
 
     const buildIsCompatible = (build) => {

engine/src/flutter/lib/web_ui/flutter_js/src/types.d.ts

@@ -8,8 +8,6 @@ type WasmCompileTarget = "dart2wasm";
 export type CompileTarget = JSCompileTarget | WasmCompileTarget;
 
 export type WebRenderer =
-  "auto" |
-  "html" |
   "canvaskit" |
   "skwasm";
 

engine/src/flutter/lib/web_ui/lib/src/engine/configuration.dart

@@ -172,12 +172,6 @@ class FlutterConfiguration {
   // runtime. They must be static constants for the compiler to remove dead code
   // effectively.
 
-  /// Auto detect which rendering backend to use.
-  ///
-  /// Using flutter tools option "--web-renderer=auto" would set the value to
-  /// true. Otherwise, it would be false.
-  static const bool flutterWebAutoDetect = bool.fromEnvironment('FLUTTER_WEB_AUTO_DETECT');
-
   static const bool flutterWebUseSkwasm = bool.fromEnvironment('FLUTTER_WEB_USE_SKWASM');
 
   /// Enable the Skia-based rendering backend.

engine/src/flutter/lib/web_ui/lib/src/engine/html_image_element_codec.dart

@@ -39,9 +39,7 @@ abstract class HtmlImageElementCodec implements ui.Codec {
     // builders to create UI.
     chunkCallback?.call(0, 100);
     imgElement = createDomHTMLImageElement();
-    if (renderer is! HtmlRenderer) {
-      imgElement!.crossOrigin = 'anonymous';
-    }
+    imgElement!.crossOrigin = 'anonymous';
     imgElement!
       ..decoding = 'async'
       ..src = src;

engine/src/flutter/lib/web_ui/lib/src/engine/initialization.dart

@@ -190,12 +190,7 @@ Future<void> initializeEngineUi() async {
   ensureMetaTag('generator', 'Flutter');
 
   if (!configuration.multiViewEnabled) {
-    final EngineFlutterWindow implicitView = ensureImplicitViewInitialized(
-      hostElement: configuration.hostElement,
-    );
-    if (renderer is HtmlRenderer) {
-      ensureResourceManagerInitialized(implicitView);
-    }
+    ensureImplicitViewInitialized(hostElement: configuration.hostElement);
   }
   _initializationState = DebugEngineInitializationState.initialized;
 }

engine/src/flutter/lib/web_ui/lib/src/engine/renderer.dart

@@ -25,35 +25,13 @@ abstract class Renderer {
   factory Renderer._internal() {
     if (FlutterConfiguration.flutterWebUseSkwasm) {
       return SkwasmRenderer();
+    } else if (FlutterConfiguration.useSkia) {
+      return CanvasKitRenderer();
     } else {
-      bool useCanvasKit;
-      if (FlutterConfiguration.flutterWebAutoDetect) {
-        if (configuration.requestedRendererType != null) {
-          useCanvasKit = configuration.requestedRendererType == 'canvaskit';
-        } else {
-          // If requestedRendererType is not specified, use CanvasKit for desktop and
-          // html for mobile.
-          useCanvasKit = isDesktop;
-        }
-      } else {
-        useCanvasKit = FlutterConfiguration.useSkia;
-      }
-
-      // Warn users in development that anything other than canvaskit is deprecated.
-      assert(() {
-        if (!useCanvasKit) {
-          // The user requested 'html' or 'auto' either in the command-line or JS.
-          final String requested =
-              configuration.requestedRendererType ??
-              (FlutterConfiguration.flutterWebAutoDetect ? 'auto' : 'html');
-          printWarning(
-            'The HTML Renderer is being deprecated. Stop using the "$requested" renderer mode.'
-            '\nSee: https://docs.flutter.dev/to/web-html-renderer-deprecation',
-          );
-        }
-        return true;
-      }());
-      return useCanvasKit ? CanvasKitRenderer() : HtmlRenderer();
+      throw StateError(
+        'Wrong combination of configuration flags. Was expecting either CanvasKit or Skwasm to be '
+        'selected.',
+      );
     }
   }
 

engine/src/flutter/lib/web_ui/lib/src/engine/view_embedder/global_html_attributes.dart

@@ -25,7 +25,6 @@ class GlobalHtmlAttributes {
 
   void applyAttributes({
     required int viewId,
-    required bool autoDetectRenderer,
     required String rendererTag,
     required String buildMode,
   }) {
@@ -39,10 +38,7 @@ class GlobalHtmlAttributes {
     //     document.querySelector('flutter-view[flt-view-id="$viewId"]')
     rootElement.setAttribute(flutterViewIdAttributeName, viewId);
 
-    // How was the current renderer selected?
-    final String rendererSelection = autoDetectRenderer ? 'auto-selected' : 'requested explicitly';
-
-    hostElement.setAttribute('flt-renderer', '$rendererTag ($rendererSelection)');
+    hostElement.setAttribute('flt-renderer', rendererTag);
     hostElement.setAttribute('flt-build-mode', buildMode);
     // TODO(mdebbar): Disable spellcheck until changes in the framework and
     // engine are complete.

engine/src/flutter/lib/web_ui/lib/src/engine/window.dart

@@ -11,7 +11,6 @@ import 'package:ui/ui_web/src/ui_web.dart' as ui_web;
 
 import '../engine.dart' show DimensionsProvider, registerHotRestartListener, renderer;
 import 'browser_detection.dart';
-import 'configuration.dart';
 import 'display.dart';
 import 'dom.dart';
 import 'initialization.dart';
@@ -73,7 +72,6 @@ class EngineFlutterView implements ui.FlutterView {
     _resizeSubscription = onResize.listen(_didResize);
     _globalHtmlAttributes.applyAttributes(
       viewId: viewId,
-      autoDetectRenderer: FlutterConfiguration.flutterWebAutoDetect,
       rendererTag: renderer.rendererTag,
       buildMode: buildMode,
     );

engine/src/flutter/lib/web_ui/test/engine/view_embedder/global_html_attributes_test.dart

@@ -22,25 +22,19 @@ void doTests() {
 
       globalHtmlAttributes.applyAttributes(
         viewId: 123,
-        autoDetectRenderer: true,
         rendererTag: 'canvaskit',
         buildMode: 'release',
       );
 
       expect(rootElement.getAttribute('flt-view-id'), '123');
-      expect(hostElement.getAttribute('flt-renderer'), 'canvaskit (auto-selected)');
+      expect(hostElement.getAttribute('flt-renderer'), 'canvaskit');
       expect(hostElement.getAttribute('flt-build-mode'), 'release');
       expect(hostElement.getAttribute('spellcheck'), 'false');
 
-      globalHtmlAttributes.applyAttributes(
-        viewId: 456,
-        autoDetectRenderer: false,
-        rendererTag: 'html',
-        buildMode: 'debug',
-      );
+      globalHtmlAttributes.applyAttributes(viewId: 456, rendererTag: 'skwasm', buildMode: 'debug');
 
       expect(rootElement.getAttribute('flt-view-id'), '456');
-      expect(hostElement.getAttribute('flt-renderer'), 'html (requested explicitly)');
+      expect(hostElement.getAttribute('flt-renderer'), 'skwasm');
       expect(hostElement.getAttribute('flt-build-mode'), 'debug');
       expect(hostElement.getAttribute('spellcheck'), 'false');
     });

engine/src/flutter/lib/web_ui/test/engine/window_test.dart

@@ -551,7 +551,7 @@ Future<void> testMain() async {
     final DomElement host = createDomHTMLDivElement();
     final EngineFlutterView view = EngineFlutterView(dispatcher, host);
 
-    expect(host.getAttribute('flt-renderer'), 'canvaskit (requested explicitly)');
+    expect(host.getAttribute('flt-renderer'), 'canvaskit');
     expect(host.getAttribute('flt-build-mode'), 'debug');
 
     view.dispose();