Handle reserved Kotlin keywords (flutter#86518)

packages/flutter_tools/lib/src/template.dart

@@ -13,6 +13,12 @@ import 'base/template.dart';
 import 'cache.dart';
 import 'dart/package_map.dart';
 
+/// The Kotlin keywords which are not Java keywords.
+/// They are escaped in Kotlin files.
+///
+/// https://kotlinlang.org/docs/keyword-reference.html
+const List<String> kReservedKotlinKeywords = <String>['when', 'in'];
+
 /// Expands templates in a directory to a destination. All files that must
 /// undergo template expansion should end with the '.tmpl' extension. All files
 /// that should be replaced with the corresponding image from
@@ -322,6 +328,11 @@ class Template {
 
       if (sourceFile.path.endsWith(templateExtension)) {
         final String templateContents = sourceFile.readAsStringSync();
+        final String? androidIdentifier = context['androidIdentifier'] as String?;
+        if (finalDestinationFile.path.endsWith('.kt') && androidIdentifier != null) {
+          context['androidIdentifier'] = _escapeKotlinKeywords(androidIdentifier);
+        }
+
         final String renderedContents = _templateRenderer.renderString(templateContents, context);
 
         finalDestinationFile.writeAsStringSync(renderedContents);
@@ -360,3 +371,11 @@ Future<Directory> _templateImageDirectory(String name, FileSystem fileSystem, Lo
       .childDirectory('templates')
       .childDirectory(name);
 }
+
+String _escapeKotlinKeywords(String androidIdentifier) {
+  final List<String> segments = androidIdentifier.split('.');
+  final List<String> correctedSegments = segments.map(
+    (String segment) => kReservedKotlinKeywords.contains(segment) ? '`$segment`' : segment
+  ).toList();
+  return correctedSegments.join('.');
+}

packages/flutter_tools/test/general.shard/android/template_test.dart

@@ -0,0 +1,48 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file/file.dart';
+import 'package:file/memory.dart';
+import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/isolated/mustache_template.dart';
+import 'package:flutter_tools/src/template.dart';
+
+import '../../src/common.dart';
+
+void main() {
+
+  testWithoutContext('kotlin reserved keywords', () {
+    final FileSystem fileSystem = MemoryFileSystem.test();
+    final BufferLogger logger = BufferLogger.test();
+    final Directory rootDir = fileSystem.currentDirectory;
+    final Directory templateSource = rootDir.childDirectory('src');
+    final Directory imageSourceDir = templateSource;
+    final Directory destination = rootDir.childDirectory('dest');
+
+    const String outputClass = 'SomeClass.kt';
+
+    final File sourceFile = templateSource.childFile('$outputClass.tmpl');
+
+    templateSource.createSync();
+    sourceFile.writeAsStringSync('package {{androidIdentifier}};');
+
+    final Template template = Template(
+        templateSource,
+        imageSourceDir,
+        fileSystem: fileSystem,
+        logger: logger,
+        templateRenderer: const MustacheTemplateRenderer(),
+        templateManifest: null
+    );
+
+    final Map<String, Object> context = <String, Object>{
+      'androidIdentifier': 'in.when.there'
+    };
+    template.render(destination, context);
+
+    final File destinationFile = destination.childFile(outputClass);
+    expect(destinationFile.readAsStringSync(), equals('package `in`.`when`.there;'));
+  });
+
+}