Allow users to create samples using flutter create. (#23584)

This adds flutter create --sample which allows users to execute a command which will create a working sample app from samples embedded in the API docs.

The command looks something like this:

flutter create --sample=chip.DeletableChipAttributes.onDeleted mysample

dev/snippets/config/skeletons/application.html

@@ -20,7 +20,7 @@
   </div>
   <div class="snippet" id="longSnippet" hidden>
     <div class="snippet-description">To create a sample project with this code snippet, run:<br/>
-      <span class="snippet-create-command">flutter create --snippet={{id}} mysample</span>
+      <span class="snippet-create-command">flutter create --sample={{id}} mysample</span>
     </div>
     <div class="copyable-container">
       <button class="copy-button-overlay copy-button" title="Copy to clipboard"

packages/flutter_tools/lib/src/version.dart

@@ -19,7 +19,7 @@ import 'globals.dart';
 
 class FlutterVersion {
   @visibleForTesting
-  FlutterVersion(this._clock) {
+  FlutterVersion([this._clock = const Clock()]) {
     _channel = _runGit('git rev-parse --abbrev-ref --symbolic @{u}');
     final String branch = _runGit('git rev-parse --abbrev-ref HEAD');
     _branch = branch == 'HEAD' ? _channel : branch;

packages/flutter_tools/test/commands/create_test.dart

@@ -8,6 +8,7 @@ import 'dart:convert';
 import 'package:args/command_runner.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
+import 'package:flutter_tools/src/base/net.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/create.dart';
 import 'package:flutter_tools/src/dart/sdk.dart';
@@ -56,6 +57,7 @@ void main() {
         'ios/Flutter/AppFrameworkInfo.plist',
         'ios/Runner/AppDelegate.m',
         'ios/Runner/GeneratedPluginRegistrant.h',
+        'lib/main.dart',
       ],
     );
     return _runFlutterTest(projectDir);
@@ -719,18 +721,52 @@ void main() {
     );
   });
 
-  // Verify that we fail with an error code when the file exists.
-  testUsingContext('fails when file exists', () async {
+  testUsingContext('fails when file exists where output directory should be', () async {
     Cache.flutterRoot = '../..';
     final CreateCommand command = CreateCommand();
     final CommandRunner<void> runner = createTestCommandRunner(command);
-    final File existingFile = fs.file('${projectDir.path.toString()}/bad');
+    final File existingFile = fs.file(fs.path.join(projectDir.path, 'bad'));
     if (!existingFile.existsSync()) {
       existingFile.createSync(recursive: true);
     }
     expect(
       runner.run(<String>['create', existingFile.path]),
-      throwsToolExit(message: 'file exists'),
+      throwsToolExit(message: 'existing file'),
+    );
+  });
+
+  testUsingContext('fails overwrite when file exists where output directory should be', () async {
+    Cache.flutterRoot = '../..';
+    final CreateCommand command = CreateCommand();
+    final CommandRunner<void> runner = createTestCommandRunner(command);
+    final File existingFile = fs.file(fs.path.join(projectDir.path, 'bad'));
+    if (!existingFile.existsSync()) {
+      existingFile.createSync(recursive: true);
+    }
+    expect(
+      runner.run(<String>['create', '--overwrite', existingFile.path]),
+      throwsToolExit(message: 'existing file'),
+    );
+  });
+
+  testUsingContext('overwrites existing directory when requested', () async {
+    Cache.flutterRoot = '../..';
+    final Directory existingDirectory = fs.directory(fs.path.join(projectDir.path, 'bad'));
+    if (!existingDirectory.existsSync()) {
+      existingDirectory.createSync(recursive: true);
+    }
+    final File existingFile = fs.file(fs.path.join(existingDirectory.path, 'lib', 'main.dart'));
+    existingFile.createSync(recursive: true);
+    await _createProject(
+      fs.directory(existingDirectory.path),
+      <String>['--overwrite'],
+      <String>[
+        'android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistrant.java',
+        'lib/main.dart',
+        'ios/Flutter/AppFrameworkInfo.plist',
+        'ios/Runner/AppDelegate.m',
+        'ios/Runner/GeneratedPluginRegistrant.h',
+      ],
     );
   });
 
@@ -779,6 +815,24 @@ void main() {
       ProcessManager: () => loggingProcessManager,
     },
   );
+
+  testUsingContext('can create a sample-based project', () async {
+    await _createAndAnalyzeProject(
+      projectDir,
+      <String>['--no-pub', '--sample=foo.bar.Baz'],
+      <String>[
+        'lib/main.dart',
+        'flutter_project.iml',
+        'android/app/src/main/AndroidManifest.xml',
+        'ios/Flutter/AppFrameworkInfo.plist',
+      ],
+      unexpectedPaths: <String>['test'],
+    );
+    expect(projectDir.childDirectory('lib').childFile('main.dart').readAsStringSync(),
+      contains('void main() {}'));
+  }, timeout: allowForRemotePubInvocation, overrides: <Type, Generator>{
+    HttpClientFactory: () => () => MockHttpClient(200, result: 'void main() {}'),
+  });
 }
 
 Future<void> _createProject(
@@ -901,3 +955,62 @@ class LoggingProcessManager extends LocalProcessManager {
     );
   }
 }
+
+class MockHttpClient implements HttpClient {
+  MockHttpClient(this.statusCode, {this.result});
+
+  final int statusCode;
+  final String result;
+
+  @override
+  Future<HttpClientRequest> getUrl(Uri url) async {
+    return MockHttpClientRequest(statusCode, result: result);
+  }
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) {
+    throw 'io.HttpClient - $invocation';
+  }
+}
+
+class MockHttpClientRequest implements HttpClientRequest {
+  MockHttpClientRequest(this.statusCode, {this.result});
+
+  final int statusCode;
+  final String result;
+
+  @override
+  Future<HttpClientResponse> close() async {
+    return MockHttpClientResponse(statusCode, result: result);
+  }
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) {
+    throw 'io.HttpClientRequest - $invocation';
+  }
+}
+
+class MockHttpClientResponse extends Stream<List<int>> implements HttpClientResponse {
+  MockHttpClientResponse(this.statusCode, {this.result});
+
+  @override
+  final int statusCode;
+
+  final String result;
+
+  @override
+  String get reasonPhrase => '<reason phrase>';
+
+  @override
+  StreamSubscription<List<int>> listen(void onData(List<int> event), {
+    Function onError, void onDone(), bool cancelOnError
+  }) {
+    return Stream<List<int>>.fromIterable(<List<int>>[result.codeUnits])
+      .listen(onData, onError: onError, onDone: onDone, cancelOnError: cancelOnError);
+  }
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) {
+    throw 'io.HttpClientResponse - $invocation';
+  }
+}