Migrate to null safety

BREAKING CHANGE: this will introduce null safety and thus updates
the signature of several methods.

Author: mvanbeusekom

packages/url_launcher/url_launcher_platform_interface/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.0.0-nullsafety
+
+* Migrate to null safety.
+
 ## 1.0.8
 
 * Added webOnlyWindowName parameter

packages/url_launcher/url_launcher_platform_interface/lib/method_channel_url_launcher.dart

@@ -14,7 +14,7 @@ const MethodChannel _channel = MethodChannel('plugins.flutter.io/url_launcher');
 /// An implementation of [UrlLauncherPlatform] that uses method channels.
 class MethodChannelUrlLauncher extends UrlLauncherPlatform {
   @override
-  Future<bool> canLaunch(String url) {
+  Future<bool?> canLaunch(String url) {
     return _channel.invokeMethod<bool>(
       'canLaunch',
       <String, Object>{'url': url},
@@ -27,15 +27,15 @@ class MethodChannelUrlLauncher extends UrlLauncherPlatform {
   }
 
   @override
-  Future<bool> launch(
+  Future<bool?> launch(
     String url, {
-    @required bool useSafariVC,
-    @required bool useWebView,
-    @required bool enableJavaScript,
-    @required bool enableDomStorage,
-    @required bool universalLinksOnly,
-    @required Map<String, String> headers,
-    String webOnlyWindowName,
+    required bool useSafariVC,
+    required bool useWebView,
+    required bool enableJavaScript,
+    required bool enableDomStorage,
+    required bool universalLinksOnly,
+    required Map<String, String> headers,
+    String? webOnlyWindowName,
   }) {
     return _channel.invokeMethod<bool>(
       'launch',

packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart

@@ -39,23 +39,23 @@ abstract class UrlLauncherPlatform extends PlatformInterface {
   }
 
   /// Returns `true` if this platform is able to launch [url].
-  Future<bool> canLaunch(String url) {
+  Future<bool?> canLaunch(String url) {
     throw UnimplementedError('canLaunch() has not been implemented.');
   }
 
   /// Returns `true` if the given [url] was successfully launched.
   ///
   /// For documentation on the other arguments, see the `launch` documentation
   /// in `package:url_launcher/url_launcher.dart`.
-  Future<bool> launch(
+  Future<bool?> launch(
     String url, {
-    @required bool useSafariVC,
-    @required bool useWebView,
-    @required bool enableJavaScript,
-    @required bool enableDomStorage,
-    @required bool universalLinksOnly,
-    @required Map<String, String> headers,
-    String webOnlyWindowName,
+    required bool useSafariVC,
+    required bool useWebView,
+    required bool enableJavaScript,
+    required bool enableDomStorage,
+    required bool universalLinksOnly,
+    required Map<String, String> headers,
+    String? webOnlyWindowName,
   }) {
     throw UnimplementedError('launch() has not been implemented.');
   }

packages/url_launcher/url_launcher_platform_interface/pubspec.yaml

@@ -3,20 +3,24 @@ description: A common platform interface for the url_launcher plugin.
 homepage: https://github.com/flutter/plugins/tree/master/packages/url_launcher/url_launcher_platform_interface
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 1.0.8
+version: 2.0.0-nullsafety
 
 dependencies:
   flutter:
     sdk: flutter
-  meta: ^1.0.5
-  plugin_platform_interface: ^1.0.1
+  # TODO (mvanbeusekom): use pub.dev once 1.10.0-nullsafety released.
+  plugin_platform_interface:
+    git: 
+      url: https://github.com/flutter/plugins.git
+      ref: nnbd
+      path: packages/plugin_platform_interface
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
   mockito: ^4.1.1
-  pedantic: ^1.8.0
+  pedantic: ^1.10.0-nullsafety.1
 
 environment:
-  sdk: ">=2.1.0 <3.0.0"
+  sdk: '>=2.10.0-56.0.dev <3.0.0'
   flutter: ">=1.9.1+hotfix.4 <2.0.0"

packages/url_launcher/url_launcher_platform_interface/test/method_channel_url_launcher_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// TODO(mvanbeusekom): Remove once Mockito is migrated to null safety.
+// @dart = 2.9
 import 'package:mockito/mockito.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';