hasLeadingUnderscore extension cleanup (#4274)

Author: pq

lib/src/rules/no_leading_underscores_for_library_prefixes.dart

@@ -6,7 +6,7 @@ import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 
 import '../analyzer.dart';
-import '../utils.dart';
+import '../util/ascii_utils.dart';
 
 const _desc = r'Avoid leading underscores for library prefixes.';
 
@@ -62,7 +62,7 @@ class _Visitor extends SimpleAstVisitor<void> {
       return;
     }
 
-    if (hasLeadingUnderscore(id.name)) {
+    if (id.name.hasLeadingUnderscore) {
       rule.reportLint(id, arguments: [id.name]);
     }
   }

lib/src/rules/no_leading_underscores_for_local_identifiers.dart

@@ -8,7 +8,6 @@ import 'package:analyzer/dart/ast/visitor.dart';
 
 import '../analyzer.dart';
 import '../util/ascii_utils.dart';
-import '../utils.dart';
 
 const _desc = r'Avoid leading underscores for local identifiers.';
 
@@ -87,7 +86,7 @@ class _Visitor extends SimpleAstVisitor<void> {
 
   void checkIdentifier(Token? id) {
     if (id == null) return;
-    if (!hasLeadingUnderscore(id.lexeme)) return;
+    if (!id.lexeme.hasLeadingUnderscore) return;
     if (id.lexeme.isJustUnderscores) return;
 
     rule.reportLintForToken(id, arguments: [id.lexeme]);

lib/src/util/ascii_utils.dart

@@ -60,6 +60,9 @@ bool isValidDartFileName(String name) {
 }
 
 extension StringExtensions on String {
+  /// Returns `true` if `this` has a leading `_`.
+  bool get hasLeadingUnderscore => startsWith('_');
+
   /// Returns whether `this` is just underscores.
   bool get isJustUnderscores {
     if (isEmpty) {

lib/src/utils.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'ast.dart';
+import 'util/ascii_utils.dart';
 
 // An identifier here is defined as:
 // * A sequence of `_`, `$`, letters or digits,
@@ -49,7 +50,8 @@ final _pubspec = RegExp(r'^_?pubspec\.yaml$');
 final _validLibraryPrefix = RegExp(r'^\$?_*[a-z][_a-z\d]*$');
 
 /// Returns `true` if the given [name] has a leading `_`.
-bool hasLeadingUnderscore(String name) => name.startsWith('_');
+@Deprecated('Prefer: ascii_utils String extension `hasLeadingUnderscore`')
+bool hasLeadingUnderscore(String name) => name.hasLeadingUnderscore;
 
 /// Check if this [string] is formatted in `CamelCase`.
 bool isCamelCase(String string) => CamelCaseString.isCamelCase(string);