Pass a language version to DartFormatter().

pkgs/intl_translation/bin/make_examples_const.dart

@@ -10,10 +10,11 @@ import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:dart_style/dart_style.dart';
+import 'package:intl_translation/src/language_version.dart';
 import 'package:intl_translation/src/message_rewriter.dart';
 import 'package:intl_translation/src/messages/main_message.dart';
 
-void main(List<String> args) {
+Future<void> main(List<String> args) async {
   var parser = ArgParser();
   var rest = parser.parse(args).rest;
   if (rest.isEmpty) {
@@ -24,7 +25,6 @@ void main(List<String> args) {
     exit(0);
   }
 
-  var formatter = DartFormatter();
   for (var inputFile in rest) {
     var outputFile = inputFile;
     var file = File(inputFile);
@@ -35,6 +35,11 @@ void main(List<String> args) {
     } else {
       print('Writing new source to $outputFile');
       var out = File(outputFile);
+
+      var languageVersion = (await findPackageLanguageVersion(file)) ??
+          DartFormatter.latestLanguageVersion;
+      var formatter = DartFormatter(languageVersion: languageVersion);
+
       out.writeAsStringSync(formatter.format(newSource));
     }
   }

pkgs/intl_translation/bin/rewrite_intl_messages.dart

@@ -16,14 +16,15 @@ import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:dart_style/dart_style.dart';
+import 'package:intl_translation/src/language_version.dart';
 import 'package:intl_translation/src/message_rewriter.dart';
 
 String? outputFileOption = 'transformed_output.dart';
 
 bool useStringSubstitution = true;
 bool replace = false;
 
-void main(List<String> args) {
+Future<void> main(List<String> args) async {
   var parser = ArgParser();
   parser.addOption('output',
       defaultsTo: 'transformed_output.dart',
@@ -55,7 +56,6 @@ void main(List<String> args) {
     exit(0);
   }
 
-  var formatter = DartFormatter();
   for (var inputFile in rest) {
     var outputFile = replace ? inputFile : outputFileOption;
     var file = File(inputFile);
@@ -67,6 +67,11 @@ void main(List<String> args) {
     } else {
       print('Writing new source to $outputFile');
       var out = File(outputFile!);
+
+      var languageVersion = (await findPackageLanguageVersion(file)) ??
+          DartFormatter.latestLanguageVersion;
+      var formatter = DartFormatter(languageVersion: languageVersion);
+
       out.writeAsStringSync(formatter.format(newSource));
     }
   }

pkgs/intl_translation/lib/src/language_version.dart

@@ -0,0 +1,25 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+import 'dart:async';
+import 'dart:io';
+
+import 'package:package_config/package_config.dart';
+import 'package:pub_semver/pub_semver.dart';
+
+/// Looks for a package surrounding [file] and, if found, returns the default
+/// language version specified by that package.
+Future<Version?> findPackageLanguageVersion(File file) async {
+  try {
+    var config = await findPackageConfig(file.parent);
+    if (config?.packageOf(file.absolute.uri)?.languageVersion
+        case var languageVersion?) {
+      return Version(languageVersion.major, languageVersion.minor, 0);
+    }
+  } catch (error) {
+    // If we fail to find or read a config, just silently do nothing and
+    // default to the latest language version.
+  }
+
+  return null;
+}

pkgs/intl_translation/pubspec.yaml

@@ -18,7 +18,9 @@ dependencies:
   args: ^2.0.0
   dart_style: ^2.0.0
   intl: '>=0.18.0 <0.20.0'
+  package_config: ^2.1.0
   path: ^1.0.0
+  pub_semver: '>=1.4.4 <3.0.0'
 
 dev_dependencies:
   lints: ^4.0.0