Add desktop implementations of new methods

packages/url_launcher/url_launcher_linux/lib/url_launcher_linux.dart

@@ -51,4 +51,16 @@ class UrlLauncherLinux extends UrlLauncherPlatform {
       },
     ).then((bool? value) => value ?? false);
   }
+
+  @override
+  Future<bool> supportsMode(PreferredLaunchMode mode) async {
+    return mode == PreferredLaunchMode.platformDefault ||
+        mode == PreferredLaunchMode.externalApplication;
+  }
+
+  @override
+  Future<bool> supportsCloseForMode(PreferredLaunchMode mode) async {
+    // No supported mode is closeable.
+    return false;
+  }
 }

packages/url_launcher/url_launcher_linux/test/url_launcher_linux_test.dart

@@ -10,7 +10,7 @@ import 'package:url_launcher_platform_interface/url_launcher_platform_interface.
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
 
-  group('$UrlLauncherLinux', () {
+  group('UrlLauncherLinux', () {
     const MethodChannel channel =
         MethodChannel('plugins.flutter.io/url_launcher_linux');
     final List<MethodCall> log = <MethodCall>[];
@@ -142,6 +142,47 @@ void main() {
 
       expect(launched, false);
     });
+
+    group('supportsMode', () {
+      test('returns true for platformDefault', () async {
+        final UrlLauncherLinux launcher = UrlLauncherLinux();
+        expect(await launcher.supportsMode(PreferredLaunchMode.platformDefault),
+            true);
+      });
+
+      test('returns true for external application', () async {
+        final UrlLauncherLinux launcher = UrlLauncherLinux();
+        expect(
+            await launcher
+                .supportsMode(PreferredLaunchMode.externalApplication),
+            true);
+      });
+
+      test('returns false for other modes', () async {
+        final UrlLauncherLinux launcher = UrlLauncherLinux();
+        expect(
+            await launcher.supportsMode(
+                PreferredLaunchMode.externalNonBrowserApplication),
+            false);
+        expect(
+            await launcher.supportsMode(PreferredLaunchMode.inAppBrowserView),
+            false);
+        expect(await launcher.supportsMode(PreferredLaunchMode.inAppWebView),
+            false);
+      });
+    });
+
+    test('supportsCloseForMode returns false', () async {
+      final UrlLauncherLinux launcher = UrlLauncherLinux();
+      expect(
+          await launcher
+              .supportsCloseForMode(PreferredLaunchMode.platformDefault),
+          false);
+      expect(
+          await launcher
+              .supportsCloseForMode(PreferredLaunchMode.externalApplication),
+          false);
+    });
   });
 }
 

packages/url_launcher/url_launcher_macos/lib/url_launcher_macos.dart

@@ -57,6 +57,18 @@ class UrlLauncherMacOS extends UrlLauncherPlatform {
     return result.value;
   }
 
+  @override
+  Future<bool> supportsMode(PreferredLaunchMode mode) async {
+    return mode == PreferredLaunchMode.platformDefault ||
+        mode == PreferredLaunchMode.externalApplication;
+  }
+
+  @override
+  Future<bool> supportsCloseForMode(PreferredLaunchMode mode) async {
+    // No supported mode is closeable.
+    return false;
+  }
+
   Exception _getInvalidUrlException(String url) {
     // TODO(stuartmorgan): Make this an actual ArgumentError. This should be
     // coordinated across all platforms as a breaking change to have them all

packages/url_launcher/url_launcher_macos/test/url_launcher_macos_test.dart

@@ -106,6 +106,47 @@ void main() {
             throwsA(isA<PlatformException>()));
       });
     });
+
+    group('supportsMode', () {
+      test('returns true for platformDefault', () async {
+        final UrlLauncherMacOS launcher = UrlLauncherMacOS(api: api);
+        expect(await launcher.supportsMode(PreferredLaunchMode.platformDefault),
+            true);
+      });
+
+      test('returns true for external application', () async {
+        final UrlLauncherMacOS launcher = UrlLauncherMacOS(api: api);
+        expect(
+            await launcher
+                .supportsMode(PreferredLaunchMode.externalApplication),
+            true);
+      });
+
+      test('returns false for other modes', () async {
+        final UrlLauncherMacOS launcher = UrlLauncherMacOS(api: api);
+        expect(
+            await launcher.supportsMode(
+                PreferredLaunchMode.externalNonBrowserApplication),
+            false);
+        expect(
+            await launcher.supportsMode(PreferredLaunchMode.inAppBrowserView),
+            false);
+        expect(await launcher.supportsMode(PreferredLaunchMode.inAppWebView),
+            false);
+      });
+    });
+
+    test('supportsCloseForMode returns false', () async {
+      final UrlLauncherMacOS launcher = UrlLauncherMacOS(api: api);
+      expect(
+          await launcher
+              .supportsCloseForMode(PreferredLaunchMode.platformDefault),
+          false);
+      expect(
+          await launcher
+              .supportsCloseForMode(PreferredLaunchMode.externalApplication),
+          false);
+    });
   });
 }
 

packages/url_launcher/url_launcher_windows/lib/url_launcher_windows.dart

@@ -45,4 +45,16 @@ class UrlLauncherWindows extends UrlLauncherPlatform {
     // Failure is handled via a PlatformException from `launchUrl`.
     return true;
   }
+
+  @override
+  Future<bool> supportsMode(PreferredLaunchMode mode) async {
+    return mode == PreferredLaunchMode.platformDefault ||
+        mode == PreferredLaunchMode.externalApplication;
+  }
+
+  @override
+  Future<bool> supportsCloseForMode(PreferredLaunchMode mode) async {
+    // No supported mode is closeable.
+    return false;
+  }
 }

packages/url_launcher/url_launcher_windows/test/url_launcher_windows_test.dart

@@ -77,6 +77,45 @@ void main() {
       expect(api.argument, 'http://example.com/');
     });
   });
+
+  group('supportsMode', () {
+    test('returns true for platformDefault', () async {
+      final UrlLauncherWindows launcher = UrlLauncherWindows(api: api);
+      expect(await launcher.supportsMode(PreferredLaunchMode.platformDefault),
+          true);
+    });
+
+    test('returns true for external application', () async {
+      final UrlLauncherWindows launcher = UrlLauncherWindows(api: api);
+      expect(
+          await launcher.supportsMode(PreferredLaunchMode.externalApplication),
+          true);
+    });
+
+    test('returns false for other modes', () async {
+      final UrlLauncherWindows launcher = UrlLauncherWindows(api: api);
+      expect(
+          await launcher
+              .supportsMode(PreferredLaunchMode.externalNonBrowserApplication),
+          false);
+      expect(await launcher.supportsMode(PreferredLaunchMode.inAppBrowserView),
+          false);
+      expect(
+          await launcher.supportsMode(PreferredLaunchMode.inAppWebView), false);
+    });
+  });
+
+  test('supportsCloseForMode returns false', () async {
+    final UrlLauncherWindows launcher = UrlLauncherWindows(api: api);
+    expect(
+        await launcher
+            .supportsCloseForMode(PreferredLaunchMode.platformDefault),
+        false);
+    expect(
+        await launcher
+            .supportsCloseForMode(PreferredLaunchMode.externalApplication),
+        false);
+  });
 }
 
 class _FakeUrlLauncherApi implements UrlLauncherApi {