Stdin name search (#1566)

Use --stdin-name as a file path for inferring the language version.

If --stdin-name is given, then look for a surrounding package config to
infer the default language version from for code read from stdin. To
avoid that behavior, you can pass in a language version explicitly
using --language-version.

Fix #1530.

CHANGELOG.md

@@ -54,6 +54,19 @@
   arguments as the `dart format` command. You can invoke it with
   `dart run dart_style:format <args...>`.
 
+* **Treat the `--stdin-name` name as a path when inferring language version.**
+  When reading input on stdin, the formatter still needs to know what language
+  version to parse the code as. If the `--stdin-name` option is set, then that
+  is treated as a file path and the formatter looks for a package config
+  surrounding that file path to infer the language version from.
+
+  If you don't want that behavior, pass in an explicit language version using
+  `--language-version=`, or use `--language-version=latest` to parse the input
+  using the latest language version supported by the formatter.
+
+  If `--stdin-name` and `--language-version` are both omitted, then parses
+  stdin using the latest supported language version.
+
 ## 2.3.7
 
 * Allow passing a language version to `DartFomatter()`. Formatted code will be

lib/src/cli/format_command.dart

@@ -107,8 +107,12 @@ class FormatCommand extends Command<int> {
         help: 'Track selection (given as "start:length") through formatting.',
         hide: !verbose);
     argParser.addOption('stdin-name',
-        help: 'Use this path in error messages when input is read from stdin.',
-        defaultsTo: 'stdin',
+        help:
+            'The path that code read from stdin is treated as coming from.\n\n'
+            'This path is used in error messages and also to locate a\n'
+            'surrounding package to infer the code\'s language version.\n'
+            'To avoid searching for a surrounding package config, pass\n'
+            'in a language version using --language-version.',
         hide: !verbose);
   }
 
@@ -223,7 +227,7 @@ class FormatCommand extends Command<int> {
     if (argResults.wasParsed('stdin-name') && argResults.rest.isNotEmpty) {
       usageException('Cannot pass --stdin-name when not reading from stdin.');
     }
-    var stdinName = argResults['stdin-name'] as String;
+    var stdinName = argResults['stdin-name'] as String?;
 
     var options = FormatterOptions(
         languageVersion: languageVersion,

lib/src/io.dart

@@ -17,7 +17,7 @@ import 'source_code.dart';
 
 /// Reads and formats input from stdin until closed.
 Future<void> formatStdin(
-    FormatterOptions options, List<int>? selection, String name) async {
+    FormatterOptions options, List<int>? selection, String? path) async {
   var selectionStart = 0;
   var selectionLength = 0;
 
@@ -26,19 +26,35 @@ Future<void> formatStdin(
     selectionLength = selection[1];
   }
 
+  var languageVersion = options.languageVersion;
+  if (languageVersion == null && path != null) {
+    // TODO(rnystrom): Remove the experiment check when the experiment ships.
+    if (options.experimentFlags.contains(tallStyleExperimentFlag)) {
+      var cache = LanguageVersionCache();
+      languageVersion = await cache.find(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.
+  languageVersion ??= DartFormatter.latestLanguageVersion;
+
+  var name = path ?? 'stdin';
+
   var completer = Completer<void>();
   var input = StringBuffer();
   stdin.transform(const Utf8Decoder()).listen(input.write, onDone: () {
     var formatter = DartFormatter(
-        languageVersion:
-            options.languageVersion ?? DartFormatter.latestLanguageVersion,
+        languageVersion: languageVersion!,
         indent: options.indent,
         pageWidth: options.pageWidth,
         experimentFlags: options.experimentFlags);
     try {
       options.beforeFile(null, name);
       var source = SourceCode(input.toString(),
-          uri: name,
+          uri: path,
           selectionStart: selectionStart,
           selectionLength: selectionLength);
       var output = formatter.formatSource(source);
@@ -138,17 +154,10 @@ Future<bool> _processFile(
   // version.
   Version? languageVersion;
   if (cache != null) {
-    try {
-      // Look for a package config. If we don't find one, default to the latest
-      // language version.
-      languageVersion = await cache.find(file);
-    } catch (error) {
-      stderr.writeln('Could not read package configuration for '
-          '$displayPath:\n$error');
-      stderr.writeln('To avoid searching for a package configuration, '
-          'specify a language version using "--language-version".');
-      return false;
-    }
+    languageVersion = await cache.find(file, displayPath);
+
+    // If the lookup failed, don't try to parse the file.
+    if (languageVersion == null) return false;
   } else {
     languageVersion = options.languageVersion;
   }

lib/src/language_version_cache.dart

@@ -33,7 +33,7 @@ class LanguageVersionCache {
 
   /// Looks for a package surrounding [file] and, if found, returns the default
   /// language version specified by that package.
-  Future<Version?> find(File file) async {
+  Future<Version?> find(File file, String displayPath) async {
     Profile.begin('look up package config');
     try {
       // Use the cached version (which may be `null`) if present.
@@ -55,6 +55,12 @@ class LanguageVersionCache {
 
       // We weren't able to resolve this file's directory, so don't try again.
       return _directoryVersions[directory] = null;
+    } catch (error) {
+      stderr.writeln('Could not read package configuration for '
+          '$displayPath:\n$error');
+      stderr.writeln('To avoid searching for a package configuration, '
+          'specify a language version using "--language-version".');
+      return null;
     } finally {
       Profile.end('look up package config');
     }