[file_selector] Add macOS support (flutter#4381)

Brings file_selector_macos into flutter/plugins from FDE, with the following changes:
- Refactored slightly to allow for unit tests of almost all of the native code
- Added native unit test coverage
- Translated to Swift, to follow repo conventions for macOS plugins
- Added an in-package example (almost an exact duplicate of the app-facing version, but written against the platform interface, as is our current practice)
- Moved to an in-package method channel. As part of that, moved the flattening of type groups from Swift to Dart.

Does not currently include native UI tests to allow for end-to-end testing (since Flutter integration tests can't be used). They should be added later (they are currently blocked on flutter/flutter#90673), but the unit tests give substantial coverage, making it substantially better to move the plugin now to get those tests running.

macOS portion of flutter/flutter#70221

.cirrus.yml

@@ -338,4 +338,4 @@ task:
       native_test_script:
         - ./script/tool_runner.sh native-test --macos
       drive_script:
-        - ./script/tool_runner.sh drive-examples --macos
+        - ./script/tool_runner.sh drive-examples --macos --exclude=script/configs/exclude_integration_macos.yaml

packages/file_selector/file_selector_macos/.gitignore

@@ -0,0 +1,5 @@
+.dart_tool
+.packages
+.flutter-plugins
+.flutter-plugins-dependencies
+pubspec.lock

packages/file_selector/file_selector_macos/.metadata

@@ -0,0 +1,10 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: 6d1c244b79f3a2747281f718297ce248bd5ad099
+  channel: master
+
+project_type: plugin

packages/file_selector/file_selector_macos/AUTHORS

@@ -0,0 +1,6 @@
+# Below is a list of people and organizations that have contributed
+# to the Flutter project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.

packages/file_selector/file_selector_macos/CHANGELOG.md

@@ -0,0 +1,26 @@
+## 0.8.2
+
+* Moves source to flutter/plugins.
+* Adds native unit tests.
+* Converts native implementation to Swift.
+* Switches to an internal method channel implementation.
+
+## 0.0.4+1
+
+* Update README
+
+## 0.0.4
+
+* Treat empty filter lists the same as null.
+
+## 0.0.3
+
+* Fix README
+
+## 0.0.2
+
+* Update SDK constraint to signal compatibility with null safety.
+
+## 0.0.1
+
+* Initial macOS implementation of `file_selector`.

packages/file_selector/file_selector_macos/LICENSE

@@ -0,0 +1,25 @@
+Copyright 2013 The Flutter Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google Inc. nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/file_selector/file_selector_macos/README.md

@@ -0,0 +1,34 @@
+# file\_selector\_macos
+
+The macOS implementation of [`file_selector`][1].
+
+## Usage
+
+### Importing the package
+
+This implementation has not yet been endorsed, meaning that you need to
+[depend on `file_selector_macos`][2] in addition to
+[depending on `file_selector`][3].
+
+Once your pubspec includes the macOS implementation, you can use the
+`file_selector` APIs normally. You should not use the `file_selector_macos`
+APIs directly.
+
+### Entitlements
+
+You will need to [add an entitlement][4] for either read-only access:
+```
+	<key>com.apple.security.files.user-selected.read-only</key>
+	<true/>
+```
+or read/write access:
+```
+	<key>com.apple.security.files.user-selected.read-write</key>
+	<true/>
+```
+depending on your use case.
+
+[1]: https://pub.dev/packages/file_selector
+[2]: https://pub.dev/packages/file_selector_macos/install
+[3]: https://pub.dev/packages/file_selector/install
+[4]: https://flutter.dev/desktop#entitlements-and-the-app-sandbox

packages/file_selector/file_selector_macos/example/.gitignore

@@ -0,0 +1,48 @@
+# Miscellaneous
+*.class
+*.log
+*.pyc
+*.swp
+.DS_Store
+.atom/
+.buildlog/
+.history
+.svn/
+
+# IntelliJ related
+*.iml
+*.ipr
+*.iws
+.idea/
+
+# The .vscode folder contains launch configuration and tasks you configure in
+# VS Code which you may wish to be included in version control, so this line
+# is commented out by default.
+#.vscode/
+
+# Flutter/Dart/Pub related
+**/doc/api/
+**/ios/Flutter/.last_build_id
+.dart_tool/
+.flutter-plugins
+.flutter-plugins-dependencies
+.packages
+.pub-cache/
+.pub/
+/build/
+
+# Web related
+lib/generated_plugin_registrant.dart
+
+# Symbolication related
+app.*.symbols
+
+# Obfuscation related
+app.*.map.json
+
+# Currently only web supported
+android/
+ios/
+
+# Exceptions to above rules.
+!/packages/flutter_tools/test/data/dart_dependencies_test/**/.packages

packages/file_selector/file_selector_macos/example/.metadata

@@ -0,0 +1,10 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: 7736f3bc90270dcb0480db2ccffbf1d13c28db85
+  channel: dev
+
+project_type: app

packages/file_selector/file_selector_macos/example/README.md

@@ -0,0 +1,4 @@
+# `file_selector_macos` example
+
+Demonstrates macOS implementation of the
+[`file_selector` plugin](https://pub.dev/packages/file_selector).

packages/file_selector/file_selector_macos/example/lib/get_directory_page.dart

@@ -0,0 +1,77 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file_selector_platform_interface/file_selector_platform_interface.dart';
+import 'package:flutter/material.dart';
+
+/// Screen that allows the user to select a directory using `getDirectoryPath`,
+/// then displays the selected directory in a dialog.
+class GetDirectoryPage extends StatelessWidget {
+  Future<void> _getDirectoryPath(BuildContext context) async {
+    const String confirmButtonText = 'Choose';
+    final String? directoryPath =
+        await FileSelectorPlatform.instance.getDirectoryPath(
+      confirmButtonText: confirmButtonText,
+    );
+    if (directoryPath == null) {
+      // Operation was canceled by the user.
+      return;
+    }
+    await showDialog<void>(
+      context: context,
+      builder: (BuildContext context) => TextDisplay(directoryPath),
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Open a text file'),
+      ),
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: <Widget>[
+            ElevatedButton(
+              style: ElevatedButton.styleFrom(
+                primary: Colors.blue,
+                onPrimary: Colors.white,
+              ),
+              child: const Text('Press to ask user to choose a directory'),
+              onPressed: () => _getDirectoryPath(context),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}
+
+/// Widget that displays a text file in a dialog.
+class TextDisplay extends StatelessWidget {
+  /// Creates a `TextDisplay`.
+  const TextDisplay(this.directoryPath);
+
+  /// The path selected in the dialog.
+  final String directoryPath;
+
+  @override
+  Widget build(BuildContext context) {
+    return AlertDialog(
+      title: const Text('Selected Directory'),
+      content: Scrollbar(
+        child: SingleChildScrollView(
+          child: Text(directoryPath),
+        ),
+      ),
+      actions: <Widget>[
+        TextButton(
+          child: const Text('Close'),
+          onPressed: () => Navigator.pop(context),
+        ),
+      ],
+    );
+  }
+}

packages/file_selector/file_selector_macos/example/lib/home_page.dart

@@ -0,0 +1,57 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+/// Home Page of the application.
+class HomePage extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final ButtonStyle style = ElevatedButton.styleFrom(
+      primary: Colors.blue,
+      onPrimary: Colors.white,
+    );
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('File Selector Demo Home Page'),
+      ),
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: <Widget>[
+            ElevatedButton(
+              style: style,
+              child: const Text('Open a text file'),
+              onPressed: () => Navigator.pushNamed(context, '/open/text'),
+            ),
+            const SizedBox(height: 10),
+            ElevatedButton(
+              style: style,
+              child: const Text('Open an image'),
+              onPressed: () => Navigator.pushNamed(context, '/open/image'),
+            ),
+            const SizedBox(height: 10),
+            ElevatedButton(
+              style: style,
+              child: const Text('Open multiple images'),
+              onPressed: () => Navigator.pushNamed(context, '/open/images'),
+            ),
+            const SizedBox(height: 10),
+            ElevatedButton(
+              style: style,
+              child: const Text('Save a file'),
+              onPressed: () => Navigator.pushNamed(context, '/save/text'),
+            ),
+            const SizedBox(height: 10),
+            ElevatedButton(
+              style: style,
+              child: const Text('Open a get directory dialog'),
+              onPressed: () => Navigator.pushNamed(context, '/directory'),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

packages/file_selector/file_selector_macos/example/lib/main.dart

@@ -0,0 +1,37 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:example/get_directory_page.dart';
+import 'package:example/home_page.dart';
+import 'package:example/open_image_page.dart';
+import 'package:example/open_multiple_images_page.dart';
+import 'package:example/open_text_page.dart';
+import 'package:example/save_text_page.dart';
+import 'package:flutter/material.dart';
+
+void main() {
+  runApp(MyApp());
+}
+
+/// MyApp is the Main Application.
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'File Selector Demo',
+      theme: ThemeData(
+        primarySwatch: Colors.blue,
+        visualDensity: VisualDensity.adaptivePlatformDensity,
+      ),
+      home: HomePage(),
+      routes: <String, WidgetBuilder>{
+        '/open/image': (BuildContext context) => OpenImagePage(),
+        '/open/images': (BuildContext context) => OpenMultipleImagesPage(),
+        '/open/text': (BuildContext context) => OpenTextPage(),
+        '/save/text': (BuildContext context) => SaveTextPage(),
+        '/directory': (BuildContext context) => GetDirectoryPage(),
+      },
+    );
+  }
+}