[flutter_tool] Fix crash in update-packages (#71950)

packages/flutter_tools/lib/src/commands/update_packages.dart

@@ -320,6 +320,7 @@ class UpdatePackagesCommand extends FlutterCommand {
         Directory temporaryFlutterSdk;
         if (upgrade) {
           temporaryFlutterSdk = createTemporaryFlutterSdk(
+            globals.logger,
             globals.fs,
             globals.fs.directory(Cache.flutterRoot),
             pubspecs,
@@ -1417,7 +1418,13 @@ String _computeChecksum(Iterable<String> names, String getVersion(String name))
 
 /// Create a synthetic Flutter SDK so that pub version solving does not get
 /// stuck on the old versions.
-Directory createTemporaryFlutterSdk(FileSystem fileSystem, Directory realFlutter, List<PubspecYaml> pubspecs) {
+@visibleForTesting
+Directory createTemporaryFlutterSdk(
+  Logger logger,
+  FileSystem fileSystem,
+  Directory realFlutter,
+  List<PubspecYaml> pubspecs,
+) {
   final Set<String> currentPackages = realFlutter
     .childDirectory('packages')
     .listSync()
@@ -1445,6 +1452,12 @@ Directory createTemporaryFlutterSdk(FileSystem fileSystem, Directory realFlutter
       .childFile('pubspec.yaml')
       ..createSync(recursive: true);
     final PubspecYaml pubspecYaml = pubspecsByName[flutterPackage];
+    if (pubspecYaml == null) {
+      logger.printError(
+        "Unexpected package '$flutterPackage' found in packages directory",
+      );
+      continue;
+    }
     final StringBuffer output = StringBuffer('name: $flutterPackage\n');
 
     // Fill in SDK dependency constraint.

packages/flutter_tools/test/general.shard/update_packages_test.dart

@@ -5,6 +5,7 @@
 import 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/commands/update_packages.dart';
 
 import '../src/common.dart';
@@ -47,6 +48,17 @@ dev_dependencies:
 # PUBSPEC CHECKSUM: 1437
 ''';
 
+const String kExtraPubspecYaml = r'''
+name: nodeps
+author: Flutter Authors <flutter-dev@googlegroups.com>
+description: A dummy pubspec with no dependencies
+homepage: http://flutter.dev
+
+environment:
+  # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
+  sdk: ">=2.2.2 <3.0.0"
+''';
+
 const String kInvalidGitPubspec = '''
 name: flutter
 author: Flutter Authors <flutter-dev@googlegroups.com>
@@ -89,6 +101,15 @@ void main() {
       .childFile('pubspec.yaml')
       .writeAsStringSync(kFlutterPubspecYaml);
 
+    // A stray extra package should not cause a crash.
+    final Directory extra = flutterSdk
+      .childDirectory('packages')
+      .childDirectory('extra')
+      ..createSync(recursive: true);
+    extra
+      .childFile('pubspec.yaml')
+      .writeAsStringSync(kExtraPubspecYaml);
+
     // Create already parsed pubspecs.
     final PubspecYaml flutterPubspec = PubspecYaml(flutter);
 
@@ -101,7 +122,9 @@ void main() {
       ref: d00362e6bdd0f9b30bba337c358b9e4a6e4ca950
 ''',
     );
+    final BufferLogger bufferLogger = BufferLogger.test();
     final Directory result = createTemporaryFlutterSdk(
+      bufferLogger,
       fileSystem,
       flutterSdk,
       <PubspecYaml>[flutterPubspec],
@@ -109,6 +132,12 @@ void main() {
 
     expect(result, exists);
 
+    // We get a warning about the unexpected package.
+    expect(
+      bufferLogger.errorText,
+      contains("Unexpected package 'extra' found in packages directory"),
+    );
+
     // The version file exists.
     expect(result.childFile('version'), exists);
     expect(result.childFile('version').readAsStringSync(), '1.2.3');