LibUnicode: Add lexer to test if a string matches the "type" production

Tests/LibUnicode/TestUnicodeLocale.cpp

@@ -69,6 +69,24 @@ TEST_CASE(is_unicode_variant_subtag)
     EXPECT(!Unicode::is_unicode_variant_subtag("a234"sv));
 }
 
+TEST_CASE(is_type_identifier)
+{
+    EXPECT(Unicode::is_type_identifier("aaaa"sv));
+    EXPECT(Unicode::is_type_identifier("aaaa-bbbb"sv));
+    EXPECT(Unicode::is_type_identifier("aaaa-bbbb-cccc"sv));
+
+    EXPECT(Unicode::is_type_identifier("1aaa"sv));
+    EXPECT(Unicode::is_type_identifier("12aa"sv));
+    EXPECT(Unicode::is_type_identifier("123a"sv));
+    EXPECT(Unicode::is_type_identifier("1234"sv));
+
+    EXPECT(!Unicode::is_type_identifier(""sv));
+    EXPECT(!Unicode::is_type_identifier("a"sv));
+    EXPECT(!Unicode::is_type_identifier("aa"sv));
+    EXPECT(!Unicode::is_type_identifier("aaaaaaaaa"sv));
+    EXPECT(!Unicode::is_type_identifier("aaaa-"sv));
+}
+
 TEST_CASE(parse_unicode_locale_id)
 {
     auto fail = [](StringView locale) {

Userland/Libraries/LibUnicode/Locale.cpp

@@ -114,6 +114,22 @@ static Optional<StringView> consume_next_segment(GenericLexer& lexer, bool with_
     return segment;
 }
 
+bool is_type_identifier(StringView identifier)
+{
+    // type = alphanum{3,8} (sep alphanum{3,8})*
+    GenericLexer lexer { identifier };
+
+    while (true) {
+        auto type = consume_next_segment(lexer, lexer.tell() > 0);
+        if (!type.has_value())
+            break;
+        if (!is_single_type(*type))
+            return false;
+    }
+
+    return lexer.is_eof() && (lexer.tell() > 0);
+}
+
 static Optional<LanguageID> parse_unicode_language_id(GenericLexer& lexer)
 {
     // https://unicode.org/reports/tr35/#Unicode_language_identifier

Userland/Libraries/LibUnicode/Locale.h

@@ -62,6 +62,7 @@ bool is_unicode_language_subtag(StringView);
 bool is_unicode_script_subtag(StringView);
 bool is_unicode_region_subtag(StringView);
 bool is_unicode_variant_subtag(StringView);
+bool is_type_identifier(StringView);
 
 Optional<LanguageID> parse_unicode_language_id(StringView);
 Optional<LocaleID> parse_unicode_locale_id(StringView);