LibUnicode: Extract canonicalization of Unicode extension values

LibJS will need to canonicalize Unicode extension values, so extract the
lambda that was doing this work to its own function. This also changes
the helpers it invokes to take the provided key as a StringView because
we don't need (and won't always have) full String objects here.

Userland/Libraries/LibUnicode/Locale.cpp

@@ -475,7 +475,7 @@ Optional<LocaleID> parse_unicode_locale_id(StringView locale)
     return locale_id;
 }
 
-static void perform_hard_coded_key_value_substitutions(String& key, String& value)
+static void perform_hard_coded_key_value_substitutions(StringView key, String& value)
 {
     // FIXME: In the XML export of CLDR, there are some aliases defined in the following files:
     // https://github.com/unicode-org/cldr-staging/blob/master/production/common/bcp47/calendar.xml
@@ -540,6 +540,33 @@ static void perform_hard_coded_key_value_substitutions(String& key, String& valu
     }
 }
 
+void canonicalize_unicode_extension_values(StringView key, String& value, bool remove_true)
+{
+    value = value.to_lowercase();
+    perform_hard_coded_key_value_substitutions(key, value);
+
+    // Note: The spec says to remove "true" type and tfield values but that is believed to be a bug in the spec
+    // because, for tvalues, that would result in invalid syntax:
+    //     https://unicode-org.atlassian.net/browse/CLDR-14318
+    // This has also been noted by test262:
+    //     https://github.com/tc39/test262/blob/18bb955771669541c56c28748603f6afdb2e25ff/test/intl402/Intl/getCanonicalLocales/transformed-ext-canonical.js
+    if (remove_true && (value == "true"sv)) {
+        value = {};
+        return;
+    }
+
+    if (key.is_one_of("sd"sv, "rg"sv)) {
+        if (auto alias = resolve_subdivision_alias(value); alias.has_value()) {
+            auto aliases = alias->split_view(' ');
+
+            // FIXME: Subdivision subtags do not appear in the CLDR likelySubtags.json file.
+            //        Implement the spec's recommendation of using just the first alias for now,
+            //        but we should determine if there's anything else needed here.
+            value = aliases[0].to_string();
+        }
+    }
+}
+
 static void transform_unicode_locale_id_to_canonical_syntax(LocaleID& locale_id)
 {
     auto canonicalize_language = [](LanguageID& language_id, bool force_lowercase) {
@@ -594,34 +621,6 @@ static void transform_unicode_locale_id_to_canonical_syntax(LocaleID& locale_id)
         }
     };
 
-    auto canonicalize_key_value_list = [&](auto& key, auto& value, bool remove_true_values) {
-        key = key.to_lowercase();
-        value = value.to_lowercase();
-
-        perform_hard_coded_key_value_substitutions(key, value);
-
-        // Note: The spec says to remove "true" type and tfield values but that is believed to be a bug in the spec
-        // because, for tvalues, that would result in invalid syntax:
-        //     https://unicode-org.atlassian.net/browse/CLDR-14318
-        // This has also been noted by test262:
-        //     https://github.com/tc39/test262/blob/18bb955771669541c56c28748603f6afdb2e25ff/test/intl402/Intl/getCanonicalLocales/transformed-ext-canonical.js
-        if (remove_true_values && (value == "true"sv)) {
-            value = {};
-            return;
-        }
-
-        if (key.is_one_of("sd"sv, "rg"sv)) {
-            if (auto alias = resolve_subdivision_alias(value); alias.has_value()) {
-                auto aliases = alias->split_view(' ');
-
-                // FIXME: Subdivision subtags do not appear in the CLDR likelySubtags.json file.
-                //        Implement the spec's recommendation of using just the first alias for now,
-                //        but we should determine if there's anything else needed here.
-                value = aliases[0].to_string();
-            }
-        }
-    };
-
     canonicalize_language(locale_id.language_id, false);
 
     quick_sort(locale_id.extensions, [](auto const& left, auto const& right) {
@@ -640,8 +639,11 @@ static void transform_unicode_locale_id_to_canonical_syntax(LocaleID& locale_id)
             [&](LocaleExtension& ext) {
                 for (auto& attribute : ext.attributes)
                     attribute = attribute.to_lowercase();
-                for (auto& keyword : ext.keywords)
-                    canonicalize_key_value_list(keyword.key, keyword.value, true);
+
+                for (auto& keyword : ext.keywords) {
+                    keyword.key = keyword.key.to_lowercase();
+                    canonicalize_unicode_extension_values(keyword.key, keyword.value, true);
+                }
 
                 quick_sort(ext.attributes);
                 quick_sort(ext.keywords, [](auto const& a, auto const& b) { return a.key < b.key; });
@@ -650,8 +652,10 @@ static void transform_unicode_locale_id_to_canonical_syntax(LocaleID& locale_id)
                 if (ext.language.has_value())
                     canonicalize_language(*ext.language, true);
 
-                for (auto& field : ext.fields)
-                    canonicalize_key_value_list(field.key, field.value, false);
+                for (auto& field : ext.fields) {
+                    field.key = field.key.to_lowercase();
+                    canonicalize_unicode_extension_values(field.key, field.value, false);
+                }
 
                 quick_sort(ext.fields, [](auto const& a, auto const& b) { return a.key < b.key; });
             },

Userland/Libraries/LibUnicode/Locale.h

@@ -127,6 +127,8 @@ bool is_type_identifier(StringView);
 
 Optional<LanguageID> parse_unicode_language_id(StringView);
 Optional<LocaleID> parse_unicode_locale_id(StringView);
+
+void canonicalize_unicode_extension_values(StringView key, String& value, bool remove_true);
 Optional<String> canonicalize_unicode_locale_id(LocaleID&);
 
 String const& default_locale();