Use the latest language version if we can't find a package.

lib/src/io.dart

@@ -35,12 +35,10 @@ Future<void> formatStdin(
   if (languageVersion == null && path != null && cache != null) {
     // We have a stdin-name, so look for a surrounding package config.
     languageVersion = await cache.findLanguageVersion(File(path), path);
-
-    // If the lookup failed, don't try to parse the code.
-    if (languageVersion == null) return;
   }
 
-  // If they didn't specify a version or a path, default to the latest.
+  // If they didn't specify a version or a path, or couldn't find a package
+  // surrounding the path, then default to the latest version.
   languageVersion ??= DartFormatter.latestLanguageVersion;
 
   // Determine the page width.
@@ -164,14 +162,12 @@ Future<bool> _processFile(
   var languageVersion = options.languageVersion;
   if (languageVersion == null && cache != null) {
     languageVersion = await cache.findLanguageVersion(file, displayPath);
-
-    // If the lookup failed, don't try to parse the file.
-    if (languageVersion == null) return false;
-  } else {
-    // If they didn't specify a version or a path, default to the latest.
-    languageVersion ??= DartFormatter.latestLanguageVersion;
   }
 
+  // If they didn't specify a version and we couldn't find a surrounding
+  // package, then default to the latest version.
+  languageVersion ??= DartFormatter.latestLanguageVersion;
+
   // Determine the page width.
   var pageWidth = options.pageWidth;
   if (pageWidth == null && cache != null) {

lib/src/testing/test_file_system.dart

@@ -18,27 +18,29 @@ final class TestFileSystem implements FileSystem {
   }
 
   @override
-  Future<bool> fileExists(FileSystemPath path) async =>
-      _files.containsKey(path.testPath);
+  Future<bool> fileExists(covariant TestFileSystemPath path) async =>
+      _files.containsKey(path._path);
 
   @override
-  Future<FileSystemPath> join(FileSystemPath from, String to) async {
+  Future<FileSystemPath> join(
+      covariant TestFileSystemPath from, String to) async {
     // If it's an absolute path, discard [from].
     if (to.startsWith('|')) return TestFileSystemPath(to);
-    return TestFileSystemPath('${from.testPath}|$to');
+    return TestFileSystemPath('${from._path}|$to');
   }
 
   @override
-  Future<FileSystemPath?> parentDirectory(FileSystemPath path) async {
-    var parts = path.testPath.split('|');
+  Future<FileSystemPath?> parentDirectory(
+      covariant TestFileSystemPath path) async {
+    var parts = path._path.split('|');
     if (parts.length == 1) return null;
 
     return TestFileSystemPath(parts.sublist(0, parts.length - 1).join('|'));
   }
 
   @override
-  Future<String> readFile(FileSystemPath path) async {
-    if (_files[path.testPath] case var contents?) return contents;
+  Future<String> readFile(covariant TestFileSystemPath path) async {
+    if (_files[path._path] case var contents?) return contents;
     throw Exception('No file at "$path".');
   }
 }
@@ -51,7 +53,3 @@ final class TestFileSystemPath implements FileSystemPath {
   @override
   String toString() => _path;
 }
-
-extension on FileSystemPath {
-  String get testPath => (this as TestFileSystemPath)._path;
-}

test/cli/language_version_test.dart

@@ -26,10 +26,12 @@ extension type Meters(int value) {
 }
 ''';
 
-    test('defaults to latest language version if omitted', () async {
+    test('uses latest language version if no surrounding package', () async {
       await d.dir('code', [d.file('a.dart', extensionTypeBefore)]).create();
 
-      var process = await runFormatterOnDir();
+      // Enable the experiment to be sure that we're opting in to the new
+      // package config search.
+      var process = await runFormatterOnDir(['--enable-experiment=tall-style']);
       await process.shouldExit(0);
 
       await d.dir('code', [d.file('a.dart', extensionTypeAfter)]).validate();
@@ -160,24 +162,26 @@ main() {
       ]).validate();
     });
 
-    test('malformed', () async {
+    test('use the latest version if the package config is malformed', () async {
       await d.dir('foo', [
         d.dir('.dart_tool', [
           d.file('package_config.json', 'this no good json is bad json'),
         ]),
-        d.file('main.dart', 'main() {}'),
+        d.file('main.dart', 'main() {var (a,b)=(1,2);}'),
       ]).create();
 
-      var path = p.join(d.sandbox, 'foo', 'main.dart');
       // TODO(rnystrom): Remove experiment flag when it ships.
-      var process =
-          await runFormatter([path, '--enable-experiment=tall-style']);
+      var process = await runFormatterOnDir(['--enable-experiment=tall-style']);
+      await process.shouldExit(0);
 
-      expect(
-          await process.stderr.next,
-          allOf(startsWith('Could not read package configuration for'),
-              contains(p.join('foo', 'main.dart'))));
-      await process.shouldExit(65);
+      // Formats the file.
+      await d.dir('foo', [
+        d.file('main.dart', '''
+main() {
+  var (a, b) = (1, 2);
+}
+''')
+      ]).validate();
     });
   });
 
@@ -235,5 +239,20 @@ main() {
       expect(await process.stdout.next, '}');
       await process.shouldExit(0);
     });
+
+    test('use latest language version if no surrounding package', () async {
+      await d.dir('foo', []).create();
+
+      var process = await runFormatter(
+          ['--enable-experiment=tall-style', '--stdin-name=foo/main.dart']);
+      // Use some relatively recent syntax.
+      process.stdin.writeln('main() {var (a,b)=(1,2);}');
+      await process.stdin.close();
+
+      expect(await process.stdout.next, 'main() {');
+      expect(await process.stdout.next, '  var (a, b) = (1, 2);');
+      expect(await process.stdout.next, '}');
+      await process.shouldExit(0);
+    });
   });
 }