[flutter_tools] Discover pubspec.yaml in parent directories (#48548)

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:args/args.dart';
 import 'package:args/command_runner.dart';
+import 'package:file/file.dart';
 import 'package:meta/meta.dart';
 import 'package:quiver/strings.dart';
 
@@ -707,8 +708,20 @@ abstract class FlutterCommand extends Command<void> {
   Future<void> validateCommand() async {
     if (_requiresPubspecYaml && !PackageMap.isUsingCustomPackagesPath) {
       // Don't expect a pubspec.yaml file if the user passed in an explicit .packages file path.
-      if (!globals.fs.isFileSync('pubspec.yaml')) {
-        throw ToolExit(userMessages.flutterNoPubspec);
+
+      // If there is no pubspec in the current directory, look in the parent
+      // until one can be found.
+      bool changedDirectory = false;
+      while (!globals.fs.isFileSync('pubspec.yaml')) {
+        final Directory nextCurrent = globals.fs.currentDirectory.parent;
+        if (nextCurrent == null || nextCurrent.path == globals.fs.currentDirectory.path) {
+          throw ToolExit(userMessages.flutterNoPubspec);
+        }
+        globals.fs.currentDirectory = nextCurrent;
+        changedDirectory = true;
+      }
+      if (changedDirectory) {
+        globals.printStatus('Changing current working directory to: ${globals.fs.currentDirectory.path}');
       }
 
       // Validate the current package map only if we will not be running "pub get" later.

packages/flutter_tools/test/commands.shard/hermetic/run_test.dart

@@ -125,6 +125,58 @@ void main() {
       DeviceManager: () => MockDeviceManager(),
     });
 
+    testUsingContext('Walks upward looking for a pubspec.yaml and succeeds if found', () async {
+      globals.fs.file('pubspec.yaml').createSync();
+      globals.fs.file('.packages')
+        ..createSync()
+        ..writeAsStringSync('Not a valid package');
+
+      globals.fs.currentDirectory = globals.fs.directory(globals.fs.path.join('a', 'b', 'c'))
+        ..createSync(recursive: true);
+
+      final RunCommand command = RunCommand();
+      applyMocksToCommand(command);
+      try {
+        await createTestCommandRunner(command).run(<String>[
+          'run',
+          '--fast-start',
+          '--no-pub',
+        ]);
+        fail('Expect exception');
+      } catch (e) {
+        expect(e, isInstanceOf<ToolExit>());
+      }
+      final BufferLogger bufferLogger = globals.logger as BufferLogger;
+      expect(bufferLogger.statusText, contains(
+        'Changing current working directory to:'
+      ));
+    }, overrides: <Type, Generator>{
+      FileSystem: () => MemoryFileSystem(),
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+
+    testUsingContext('Walks upward looking for a pubspec.yaml and exits if missing', () async {
+      globals.fs.currentDirectory = globals.fs.directory(globals.fs.path.join('a', 'b', 'c'))
+        ..createSync(recursive: true);
+
+      final RunCommand command = RunCommand();
+      applyMocksToCommand(command);
+      try {
+        await createTestCommandRunner(command).run(<String>[
+          'run',
+          '--fast-start',
+          '--no-pub',
+        ]);
+        fail('Expect exception');
+      } catch (e) {
+        expect(e, isInstanceOf<ToolExit>());
+        expect(e.toString(), contains('No pubspec.yaml file found'));
+      }
+    }, overrides: <Type, Generator>{
+      FileSystem: () => MemoryFileSystem(),
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+
 
     group('run app', () {
       MemoryFileSystem fs;