[flutter_web_plugins] Migrate to null safety. (flutter#69844)

Author: ditman

packages/flutter_web_plugins/lib/flutter_web_plugins.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 /// The platform channels and plugin registry implementations for
 /// the web implementations of Flutter plugins.
 ///

packages/flutter_web_plugins/lib/src/navigation/js_url_strategy.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 @JS()
 library js_location_strategy;
 
@@ -16,7 +14,7 @@ import 'package:meta/meta.dart';
 
 import 'url_strategy.dart';
 
-typedef _JsSetUrlStrategy = void Function(JsUrlStrategy);
+typedef _JsSetUrlStrategy = void Function(JsUrlStrategy?);
 
 /// A JavaScript hook to customize the URL strategy of a Flutter app.
 //
@@ -29,7 +27,7 @@ external _JsSetUrlStrategy get jsSetUrlStrategy;
 
 typedef _PathGetter = String Function();
 
-typedef _StateGetter = Object Function();
+typedef _StateGetter = Object? Function();
 
 typedef _AddPopStateListener = ui.VoidCallback Function(html.EventListener);
 
@@ -43,10 +41,6 @@ typedef _HistoryMove = Future<void> Function(int count);
 /// Given a Dart implementation of URL strategy, converts it to a JavaScript
 /// URL strategy to be passed through JS interop.
 JsUrlStrategy convertToJsUrlStrategy(UrlStrategy strategy) {
-  if (strategy == null) {
-    return null;
-  }
-
   return JsUrlStrategy(
     getPath: allowInterop(strategy.getPath),
     getState: allowInterop(strategy.getState),

packages/flutter_web_plugins/lib/src/navigation/url_strategy.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:html' as html;
 import 'dart:ui' as ui;
@@ -14,8 +12,12 @@ import 'utils.dart';
 /// Change the strategy to use for handling browser URL.
 ///
 /// Setting this to null disables all integration with the browser history.
-void setUrlStrategy(UrlStrategy strategy) {
-  jsSetUrlStrategy(convertToJsUrlStrategy(strategy));
+void setUrlStrategy(UrlStrategy? strategy) {
+  JsUrlStrategy? jsUrlStrategy;
+  if (strategy != null) {
+    jsUrlStrategy = convertToJsUrlStrategy(strategy);
+  }
+  jsSetUrlStrategy(jsUrlStrategy);
 }
 
 /// Represents and reads route state from the browser's URL.
@@ -37,7 +39,7 @@ abstract class UrlStrategy {
   /// The state of the current browser history entry.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/API/History/state
-  Object getState();
+  Object? getState();
 
   /// Given a path that's internal to the app, create the external url that
   /// will be used in the browser.
@@ -101,7 +103,7 @@ class HashUrlStrategy extends UrlStrategy {
   String getPath() {
     // the hash value is always prefixed with a `#`
     // and if it is empty then it will stay empty
-    final String path = _platformLocation.hash ?? '';
+    final String path = _platformLocation.hash;
     assert(path.isEmpty || path.startsWith('#'));
 
     // We don't want to return an empty string as a path. Instead we default to "/".
@@ -113,7 +115,7 @@ class HashUrlStrategy extends UrlStrategy {
   }
 
   @override
-  Object getState() => _platformLocation.state;
+  Object? getState() => _platformLocation.state;
 
   @override
   String prepareExternalUrl(String internalUrl) {
@@ -148,7 +150,7 @@ class HashUrlStrategy extends UrlStrategy {
   /// `history.back` transition.
   Future<void> _waitForPopState() {
     final Completer<void> completer = Completer<void>();
-    ui.VoidCallback unsubscribe;
+    late ui.VoidCallback unsubscribe;
     unsubscribe = addPopStateListener((_) {
       unsubscribe();
       completer.complete();
@@ -238,7 +240,7 @@ abstract class PlatformLocation {
   /// The `state` in the current history entry.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/API/History/state
-  Object get state;
+  Object? get state;
 
   /// Adds a new entry to the browser history stack.
   ///
@@ -266,14 +268,22 @@ abstract class PlatformLocation {
   /// The base href where the Flutter app is being served.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base
-  String getBaseHref();
+  String? getBaseHref();
 }
 
 /// Delegates to real browser APIs to provide platform location functionality.
 class BrowserPlatformLocation extends PlatformLocation {
   /// Default constructor for [BrowserPlatformLocation].
   const BrowserPlatformLocation();
 
+  // Default value for [pathname] when it's not set in window.location.
+  // According to MDN this should be ''. Chrome seems to return '/'.
+  static const String _defaultPathname = '';
+
+  // Default value for [search] when it's not set in window.location.
+  // According to both chrome, and the MDN, this is ''.
+  static const String _defaultSearch = '';
+
   html.Location get _location => html.window.location;
   html.History get _history => html.window.history;
 
@@ -288,16 +298,16 @@ class BrowserPlatformLocation extends PlatformLocation {
   }
 
   @override
-  String get pathname => _location.pathname;
+  String get pathname => _location.pathname ?? _defaultPathname;
 
   @override
-  String get search => _location.search;
+  String get search => _location.search ?? _defaultSearch;
 
   @override
   String get hash => _location.hash;
 
   @override
-  Object get state => _history.state;
+  Object? get state => _history.state;
 
   @override
   void pushState(Object state, String title, String url) {
@@ -315,6 +325,5 @@ class BrowserPlatformLocation extends PlatformLocation {
   }
 
   @override
-  String getBaseHref() => getBaseElementHrefFromDom();
-  // String getBaseHref() => html.document.baseUri;
+  String? getBaseHref() => getBaseElementHrefFromDom();
 }

packages/flutter_web_plugins/lib/src/navigation/utils.dart

@@ -2,43 +2,33 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:html';
 
-AnchorElement _urlParsingNode;
+// TODO(mdebbar): Use the `URI` class instead?
+final AnchorElement _urlParsingNode = AnchorElement();
 
 /// Extracts the pathname part of a full [url].
 ///
 /// Example: for the url `http://example.com/foo`, the extracted pathname will
 /// be `/foo`.
 String extractPathname(String url) {
-  // TODO(mdebbar): Use the `URI` class instead?
-  _urlParsingNode ??= AnchorElement();
   _urlParsingNode.href = url;
-  final String pathname = _urlParsingNode.pathname;
+  final String pathname = _urlParsingNode.pathname ?? '';
   return (pathname.isEmpty || pathname[0] == '/') ? pathname : '/$pathname';
 }
 
-Element _baseElement;
+// The <base> element in the document.
+final Element? _baseElement = document.querySelector('base');
 
-/// Finds the <base> element in the document and returns its `href` attribute.
+/// Returns the `href` attribute of the <base> element in the document.
 ///
 /// Returns null if the element isn't found.
-String getBaseElementHrefFromDom() {
-  if (_baseElement == null) {
-    _baseElement = document.querySelector('base');
-    if (_baseElement == null) {
-      return null;
-    }
-  }
-  return _baseElement.getAttribute('href');
-}
+String? getBaseElementHrefFromDom() => _baseElement?.getAttribute('href');
 
 /// Checks that [baseHref] is set.
 ///
 /// Throws an exception otherwise.
-String checkBaseHref(String baseHref) {
+String checkBaseHref(String? baseHref) {
   if (baseHref == null) {
     throw Exception('Please add a <base> element to your index.html');
   }

packages/flutter_web_plugins/lib/src/plugin_event_channel.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:flutter/services.dart';
@@ -28,14 +26,14 @@ import 'plugin_registry.dart';
 ///
 /// The first method is `listen`. When called, it begins forwarding
 /// messages to the framework side when they are added to the
-/// [controller]. This triggers the [StreamController.onListen] callback
-/// on the [controller].
+/// `controller`. This triggers the [StreamController.onListen] callback
+/// on the `controller`.
 ///
 /// The other method is `cancel`. When called, it stops forwarding
 /// events to the framework. This triggers the [StreamController.onCancel]
-/// callback on the [controller].
+/// callback on the `controller`.
 ///
-/// Events added to the [controller] when the framework is not
+/// Events added to the `controller` when the framework is not
 /// subscribed are silently discarded.
 class PluginEventChannel<T> {
   /// Creates a new plugin event channel.
@@ -45,8 +43,8 @@ class PluginEventChannel<T> {
     this.name, [
     this.codec = const StandardMethodCodec(),
     this.binaryMessenger,
-  ])  : assert(name != null),
-        assert(codec != null);
+  ]) : assert(name != null), // ignore: unnecessary_null_comparison
+       assert(codec != null); // ignore: unnecessary_null_comparison
 
   /// The logical channel on which communication happens.
   ///
@@ -63,7 +61,7 @@ class PluginEventChannel<T> {
   /// When this is null, the [pluginBinaryMessenger] is used instead,
   /// which sends messages from the platform-side to the
   /// framework-side.
-  final BinaryMessenger binaryMessenger;
+  final BinaryMessenger? binaryMessenger;
 
   /// Use [setController] instead.
   ///
@@ -81,7 +79,7 @@ class PluginEventChannel<T> {
   ///
   /// Setting the controller to null disconnects from the channel (setting
   /// the message handler on the [binaryMessenger] to null).
-  void setController(StreamController<T> controller) {
+  void setController(StreamController<T>? controller) {
     final BinaryMessenger messenger = binaryMessenger ?? pluginBinaryMessenger;
     if (controller == null) {
       messenger.setMessageHandler(name, null);
@@ -105,16 +103,21 @@ class PluginEventChannel<T> {
 }
 
 class _EventChannelHandler<T> {
-  _EventChannelHandler(this.name, this.codec, this.controller, this.messenger) : assert(messenger != null);
+  _EventChannelHandler(
+    this.name,
+    this.codec,
+    this.controller,
+    this.messenger,
+  ) : assert(messenger != null); // ignore: unnecessary_null_comparison
 
   final String name;
   final MethodCodec codec;
   final StreamController<T> controller;
   final BinaryMessenger messenger;
 
-  StreamSubscription<T> subscription;
+  StreamSubscription<T>? subscription;
 
-  Future<ByteData> handle(ByteData message) {
+  Future<ByteData>? handle(ByteData? message) {
     final MethodCall call = codec.decodeMethodCall(message);
     switch (call.method) {
       case 'listen':
@@ -128,9 +131,8 @@ class _EventChannelHandler<T> {
   }
 
   Future<ByteData> _listen() async {
-    if (subscription != null) {
-      await subscription.cancel();
-    }
+    // Cancel any existing subscription.
+    await subscription?.cancel();
     subscription = controller.stream.listen((dynamic event) {
       messenger.send(name, codec.encodeSuccessEnvelope(event));
     }, onError: (dynamic error) {
@@ -146,7 +148,7 @@ class _EventChannelHandler<T> {
         message: 'No active subscription to cancel.',
       );
     }
-    await subscription.cancel();
+    await subscription!.cancel();
     subscription = null;
     return codec.encodeSuccessEnvelope(null);
   }