[web] Provide a hook to disable location strategy

lib/web_ui/lib/src/engine/history.dart

@@ -53,6 +53,10 @@ class BrowserHistory {
     }
   }
 
+  /// Returns the currently active location strategy.
+  @visibleForTesting
+  LocationStrategy get locationStrategy => _locationStrategy;
+
   /// The path of the current location of the user's browser.
   String get currentPath => _locationStrategy?.path ?? '/';
 

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

@@ -17,6 +17,12 @@ ui.VoidCallback scheduleFrameCallback;
 class EngineWindow extends ui.Window {
   EngineWindow() {
     _addBrightnessMediaQueryListener();
+    js.context['_flutter_web_set_location_strategy'] = (LocationStrategy strategy) {
+      locationStrategy = strategy;
+    };
+    registerHotRestartListener(() {
+      js.context['_flutter_web_set_location_strategy'] = null;
+    });
   }
 
   @override
@@ -178,6 +184,10 @@ class EngineWindow extends ui.Window {
     _browserHistory.locationStrategy = strategy;
   }
 
+  /// Returns the currently active location strategy.
+  @visibleForTesting
+  LocationStrategy get locationStrategy => _browserHistory.locationStrategy;
+
   @override
   ui.VoidCallback get onTextScaleFactorChanged => _onTextScaleFactorChanged;
   ui.VoidCallback _onTextScaleFactorChanged;

lib/web_ui/test/window_test.dart

@@ -3,6 +3,9 @@
 // found in the LICENSE file.
 
 // @dart = 2.6
+import 'dart:async';
+import 'dart:html' as html;
+import 'dart:js_util' as js_util;
 import 'dart:typed_data';
 
 import 'package:test/test.dart';
@@ -12,24 +15,18 @@ const MethodCodec codec = JSONMethodCodec();
 
 void emptyCallback(ByteData date) {}
 
-TestLocationStrategy _strategy;
-TestLocationStrategy get strategy => _strategy;
-set strategy(TestLocationStrategy newStrategy) {
-  window.locationStrategy = _strategy = newStrategy;
-}
-
 void main() {
   test('window.defaultRouteName should not change', () {
-    strategy = TestLocationStrategy.fromEntry(TestHistoryEntry('initial state', null, '/initial'));
+    window.locationStrategy = TestLocationStrategy.fromEntry(TestHistoryEntry('initial state', null, '/initial'));
     expect(window.defaultRouteName, '/initial');
 
     // Changing the URL in the address bar later shouldn't affect [window.defaultRouteName].
-    strategy.replaceState(null, null, '/newpath');
+    window.locationStrategy.replaceState(null, null, '/newpath');
     expect(window.defaultRouteName, '/initial');
   });
 
   test('window.defaultRouteName should reset after navigation platform message', () {
-    strategy = TestLocationStrategy.fromEntry(TestHistoryEntry('initial state', null, '/initial'));
+    window.locationStrategy = TestLocationStrategy.fromEntry(TestHistoryEntry('initial state', null, '/initial'));
     // Reading it multiple times should return the same value.
     expect(window.defaultRouteName, '/initial');
     expect(window.defaultRouteName, '/initial');
@@ -46,4 +43,51 @@ void main() {
     // reset to "/".
     expect(window.defaultRouteName, '/');
   });
+
+  test('can disable location strategy', () async {
+    final testStrategy = TestLocationStrategy.fromEntry(
+      TestHistoryEntry(null, null, '/'),
+    );
+    window.locationStrategy = testStrategy;
+
+    expect(window.locationStrategy, testStrategy);
+    // A single listener should've been setup.
+    expect(testStrategy.listeners, hasLength(1));
+    // The initial entry should be there, plus another "flutter" entry.
+    expect(testStrategy.history, hasLength(2));
+    expect(testStrategy.history[0].state, <String, bool>{'origin': true});
+    expect(testStrategy.history[1].state, <String, bool>{'flutter': true});
+    expect(testStrategy.currentEntry, testStrategy.history[1]);
+
+    // Now, let's disable location strategy and make sure things get cleaned up.
+    expect(() => jsSetLocationStrategy(null), returnsNormally);
+    expect(window.locationStrategy, isNull);
+
+    // The listener is removed in a microtask.
+    final Completer<void> microtaskCompleter = Completer<void>.sync();
+    scheduleMicrotask(() {
+      microtaskCompleter.complete();
+    });
+    await microtaskCompleter.future;
+
+    // No more listeners.
+    expect(testStrategy.listeners, isEmpty);
+    // History should've moved back to the initial entry.
+    expect(testStrategy.history[0].state, <String, bool>{'origin': true});
+    expect(testStrategy.currentEntry, testStrategy.history[0]);
+  });
+
+  test('js interop throws on wrong type', () {
+    expect(() => jsSetLocationStrategy(123), throwsA(anything));
+    expect(() => jsSetLocationStrategy('foo'), throwsA(anything));
+    expect(() => jsSetLocationStrategy(false), throwsA(anything));
+  });
+}
+
+void jsSetLocationStrategy(dynamic strategy) {
+  js_util.callMethod(
+    html.window,
+    '_flutter_web_set_location_strategy',
+    <dynamic>[strategy],
+  );
 }