From f02becaeffe7a727a71c56765672e6d43821d6e3 Mon Sep 17 00:00:00 2001
From: ZhuchkaTriplesix <mrlololoshka94@gmail.com>
Date: Thu, 15 Oct 2026 07:49:36 +0300
Subject: [PATCH] perf(theme): walk scope prefixes by last dot in
 TokenStyleResolver

_scopePrefixes split the scope into a list and built every prefix with
sublist(0, i).join('.') up front, for each uncached scope lookup.

The resolver cuts the scope at the last dot, one prefix at a time, and stops at
the first rule that matches. The order of prefixes is the same, including
empty segments; a test pins that.

Closes #1530
---
 .../theme/parser/token_style_resolver.dart    | 16 +++++-------
 .../parser/token_style_resolver_test.dart     | 26 +++++++++++++++++++
 2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/lib/core/theme/parser/token_style_resolver.dart b/lib/core/theme/parser/token_style_resolver.dart
index acb48322..f2a8b8a4 100644
--- a/lib/core/theme/parser/token_style_resolver.dart
+++ b/lib/core/theme/parser/token_style_resolver.dart
@@ -22,21 +22,19 @@ class TokenStyleResolver {
       _cache.putIfAbsent(scope, () => _resolveUncached(scope));
 
   TextStyle _resolveUncached(String scope) {
-    for (final prefix in _scopePrefixes(scope)) {
+    // `a.b.c` -> `a.b` -> `a`: cut at the last dot instead of splitting into a
+    // list and joining sublists (#1530).
+    var prefix = scope;
+    while (true) {
       for (final rule in _rules) {
         if (rule.scopes.contains(prefix)) {
           return _styleFromRule(rule);
         }
       }
+      final dot = prefix.lastIndexOf('.');
+      if (dot < 0) return _defaultStyle;
+      prefix = prefix.substring(0, dot);
     }
-    return _defaultStyle;
-  }
-
-  List<String> _scopePrefixes(String scope) {
-    final parts = scope.split('.');
-    return [
-      for (var i = parts.length; i >= 1; i--) parts.sublist(0, i).join('.'),
-    ];
   }
 
   TextStyle _styleFromRule(TokenColorRule rule) {
diff --git a/test/core/theme/parser/token_style_resolver_test.dart b/test/core/theme/parser/token_style_resolver_test.dart
index c2badd7e..cee943f6 100644
--- a/test/core/theme/parser/token_style_resolver_test.dart
+++ b/test/core/theme/parser/token_style_resolver_test.dart
@@ -37,4 +37,30 @@ void main() {
     final b = resolver.resolve('string.quoted.double');
     expect(identical(a, b), isTrue);
   });
+
+  test('walks prefixes by dot, including empty segments (#1530)', () {
+    const rules = [
+      TokenColorRule(scopes: ['a'], foreground: '#010101'),
+      TokenColorRule(scopes: ['a.b'], foreground: '#020202'),
+      TokenColorRule(scopes: ['a.'], foreground: '#030303'),
+      TokenColorRule(scopes: [''], foreground: '#040404'),
+      TokenColorRule(scopes: ['x.y.z'], foreground: '#050505'),
+    ];
+    final resolver = TokenStyleResolver(
+      rules: rules,
+      defaultStyle: const TextStyle(color: Color(0xFFFFFFFF)),
+    );
+
+    // The longest prefix wins.
+    expect(resolver.resolve('a.b.c.d').color, const Color(0xFF020202));
+    expect(resolver.resolve('a.c.d').color, const Color(0xFF010101));
+    expect(resolver.resolve('x.y.z.w').color, const Color(0xFF050505));
+    // `a..b` -> `a.` -> `a`: the empty segment is a prefix of its own.
+    expect(resolver.resolve('a..b').color, const Color(0xFF030303));
+    // The leading dot gives the empty prefix; a bare empty scope is it too.
+    expect(resolver.resolve('.q').color, const Color(0xFF040404));
+    expect(resolver.resolve('').color, const Color(0xFF040404));
+    // Nothing matches: the default style.
+    expect(resolver.resolve('zzz.top').color, const Color(0xFFFFFFFF));
+  });
 }