disallow reserved words in package names

lib/src/ast.dart

@@ -14,6 +14,10 @@ import 'package:path/path.dart' as path;
 import 'analyzer.dart';
 import 'utils.dart';
 
+List<String>? _reservedWords;
+
+List<String> get reservedWords => _reservedWords ??= _collectReservedWords();
+
 /// Returns direct children of [parent].
 List<Element> getChildren(Element parent, [String? name]) {
   var children = <Element>[];
@@ -173,6 +177,9 @@ bool isPublicMethod(ClassMember m) {
   return declaredElement != null && isMethod(m) && declaredElement.isPublic;
 }
 
+/// Check if the given word is a Dart reserved word.
+bool isReservedWord(String word) => reservedWords.contains(word);
+
 /// Returns `true` if the given method [declaration] is a "simple getter".
 ///
 /// A simple getter takes one of these basic forms:
@@ -330,6 +337,16 @@ bool _checkForSimpleSetter(MethodDeclaration setter, Expression expression) {
   return false;
 }
 
+List<String> _collectReservedWords() {
+  var reserved = <String>[];
+  for (var entry in Keyword.keywords.entries) {
+    if (entry.value.isReservedWord) {
+      reserved.add(entry.key);
+    }
+  }
+  return reserved;
+}
+
 int? _getIntValue(Expression expression, LinterContext? context,
     {bool negated = false}) {
   int? value;

lib/src/utils.dart

@@ -2,6 +2,8 @@
 // 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 'ast.dart';
+
 // An identifier here is defined as:
 // * A sequence of `_`, `$`, letters or digits,
 // * where no `$` comes after a digit.
@@ -86,7 +88,9 @@ bool isValidLibraryPrefix(String libraryPrefix) =>
 
 /// Returns true if this [id] is a valid package name.
 bool isValidPackageName(String id) =>
-    _lowerCaseUnderScoreWithLeadingUnderscores.hasMatch(id) && isIdentifier(id);
+    _lowerCaseUnderScoreWithLeadingUnderscores.hasMatch(id) &&
+    isIdentifier(id) &&
+    !isReservedWord(id);
 
 class CamelCaseString {
   static final _camelCaseMatcher = RegExp(r'[A-Z][a-z]*');

test/utils_test.dart

@@ -25,6 +25,7 @@ void main() {
       'async',
     ], isValidPackageName, isTrue);
     testEach([
+      'break', // reserved word
       'fOO',
       'foo_',
       'foo_Bar',