Remove the old canvaskit artifacts to not confuse the web runner.

packages/flutter_tools/lib/src/flutter_cache.dart

@@ -38,6 +38,7 @@ class FlutterCache extends Cache {
     registerArtifact(AndroidInternalBuildArtifacts(this));
     registerArtifact(IOSEngineArtifacts(this, platform: platform));
     registerArtifact(FlutterWebSdk(this));
+    registerArtifact(LegacyCanvasKitRemover(this));
     registerArtifact(FlutterSdk(this, platform: platform));
     registerArtifact(WindowsEngineArtifacts(this, platform: platform));
     registerArtifact(MacOSEngineArtifacts(this, platform: platform));
@@ -184,6 +185,38 @@ class FlutterWebSdk extends CachedArtifact {
   }
 }
 
+// In previous builds, CanvasKit artifacts were stored in a different location
+// than they are now. Leaving those old artifacts in the cache confuses the
+// in-memory filesystem that the web runner uses, so this artifact will evict
+// them from our cache if they are there.
+class LegacyCanvasKitRemover extends ArtifactSet {
+  LegacyCanvasKitRemover(this.cache) : super(DevelopmentArtifact.web);
+
+  final Cache cache;
+
+  @override
+  String get name => 'legacy_canvaskit_remover';
+
+  Directory _getLegacyCanvasKitDirectory(FileSystem fileSystem) =>
+    fileSystem.directory(fileSystem.path.join(
+      cache.getRoot().path,
+      'canvaskit',
+    ));
+
+  @override
+  Future<bool> isUpToDate(FileSystem fileSystem) async =>
+    !(await _getLegacyCanvasKitDirectory(fileSystem).exists());
+
+  @override
+  Future<void> update(
+    ArtifactUpdater artifactUpdater,
+    Logger logger,
+    FileSystem fileSystem,
+    OperatingSystemUtils operatingSystemUtils,
+    {bool offline = false}
+  ) => _getLegacyCanvasKitDirectory(fileSystem).delete(recursive: true);
+}
+
 /// A cached artifact containing the dart:ui source code.
 class FlutterSdk extends EngineCachedArtifact {
   FlutterSdk(Cache cache, {

packages/flutter_tools/test/general.shard/cache_test.dart

@@ -880,6 +880,31 @@ void main() {
     ));
   });
 
+  testWithoutContext('LegacyCanvasKitRemover removes old canvaskit artifacts if they exist', () async {
+    final FileExceptionHandler handler = FileExceptionHandler();
+    final MemoryFileSystem fileSystem = MemoryFileSystem.test(opHandle: handler.opHandle);
+    final Cache cache = Cache.test(processManager: FakeProcessManager.any(), fileSystem: fileSystem);
+    final File canvasKitWasm = fileSystem.file(fileSystem.path.join(
+      cache.getRoot().path,
+      'canvaskit',
+      'canvaskit.wasm',
+    ));
+    canvasKitWasm.createSync(recursive: true);
+    canvasKitWasm.writeAsStringSync('hello world');
+
+    final LegacyCanvasKitRemover remover = LegacyCanvasKitRemover(cache);
+    expect(await remover.isUpToDate(fileSystem), false);
+    await remover.update(
+      FakeArtifactUpdater(),
+      BufferLogger.test(),
+      fileSystem,
+      FakeOperatingSystemUtils(),
+    );
+    expect(await remover.isUpToDate(fileSystem), true);
+
+    expect(canvasKitWasm.existsSync(), isFalse);
+  });
+
   testWithoutContext('Cache handles exception thrown if stamp file cannot be parsed', () {
     final FileExceptionHandler exceptionHandler = FileExceptionHandler();
     final FileSystem fileSystem = MemoryFileSystem.test(opHandle: exceptionHandler.opHandle);