Avoid guessing JavaScript from shared let and arrow syntax

tools/chatgui/src/code_language.cpp

@@ -42,7 +42,8 @@ const Rule rules[] = {
     {Php, 4, QRegularExpression(R"(\$[a-zA-Z_]\w*\s*(?:->|\[|=))")},
     {Php, 4, QRegularExpression(R"(\bfunction\s+\w+\s*\([^\n)]*\$|\b(?:public|private|protected)\s+(?:static\s+)?function\b)")},
     {Php, 3, QRegularExpression(R"(\b(?:echo|require_once|include_once)\b|\barray\s*\(|\$this\b)")},
-    {JavaScript, 4, QRegularExpression(R"(\b(?:const|let|var)\s+[a-zA-Z_$][\w$]*\s*=)")},
+    {JavaScript, 4, QRegularExpression(R"(\b(?:const|var)\s+[a-zA-Z_$][\w$]*\s*=)")},
+    {JavaScript, 2, QRegularExpression(R"(\blet\s+[a-zA-Z_$][\w$]*\s*=)")},
     {JavaScript, 3, QRegularExpression(R"(=>|\bfunction\s*[\w$]*\s*\()")},
     {JavaScript, 4, QRegularExpression(R"(\b(?:module\.exports|exports\.\w+|console\.\w+|document\.\w+)\b)")},
     {JavaScript, 4, QRegularExpression(R"(^\s*(?:export\s+(?:default|function|const|class)\b|import\s+[^;\n]+\s+from\b))",
@@ -74,10 +75,15 @@ QString detectCodeLanguage(QStringView source) {
     }
     std::array<int, LanguageCount> scores{};
     for (const auto& rule : rules) if (rule.pattern.match(code).hasMatch()) scores[rule.language] += rule.weight;
-    // Фрагменты HTML без doctype: нужен парный известный тег; JSX с объявлениями JS не выбираем как HTML.
+    // Структурные теги отличают HTML с вложенным JS/CSS; одиночный div внутри JSX недостаточен.
+    static const QRegularExpression structuralTags(R"(</?(?:html|head|body|script|style)\b[^<>]*>)",
+                                                   QRegularExpression::CaseInsensitiveOption);
     static const QRegularExpression tags(R"(<(div|span|p|a|ul|li|table|section|form|button|h[1-6])\b[^<>]*>[\s\S]*?</\1\s*>)",
                                         QRegularExpression::CaseInsensitiveOption);
-    if (scores[JavaScript] == 0 && tags.match(code).hasMatch()) { scores[Html] = 7; scores[Css] = 0; }
+    if (structuralTags.match(code).hasMatch() || (scores[JavaScript] == 0 && tags.match(code).hasMatch())) {
+        GUI_DEBUG("code language: result=HTML markup tags sampled=%d", int(sample.size()));
+        return QStringLiteral("HTML");
+    }
     // std:: и Type::method встречаются также в Rust; use/fn/impl отличают его от C++.
     if (scores[Rust] >= 7) scores[Cpp] = 0;
     // C является подмножеством C++: специфичные конструкции C++ имеют приоритет.

tools/chatgui/tests/test_code_language.cpp

@@ -29,6 +29,9 @@ private slots:
         QTest::newRow("html") << "<!doctype html>\n<html><script>const f = () => 1;</script></html>" << "HTML";
         QTest::newRow("html-fragment") << "<div class=\"hello\"><span>Hello</span></div>" << "HTML";
         QTest::newRow("html-css") << "<style>.x { color: red; margin: 1px; }</style><p>Hello</p>" << "HTML";
+        QTest::newRow("html-js") << "<script>document.addEventListener('load', function() {});</script>" << "HTML";
+        QTest::newRow("html-script-list") << "<script src=\"test.js\"></script>" << "HTML";
+        QTest::newRow("ambiguous-let-arrow") << "let x = match value { Value::A => true, Value::B => false };" << "";
         QTest::newRow("empty") << "" << "";
         QTest::newRow("ambiguous") << "int x = 42;" << "";
         QTest::newRow("prose") << "Java and Kotlin have class and function declarations; use CSS for color." << "";