LibJS: Implement Intl.Locale.prototype.maximize

Author: https://github.com/trflynn89
Commit: https://github.com/SerenityOS/serenity/commit/0b1f5118d56
Pull-request: https://github.com/SerenityOS/serenity/pull/9770
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -281,6 +281,7 @@ namespace JS {
     P(log10)                                 \
     P(map)                                   \
     P(max)                                   \
+    P(maximize)                              \
     P(mergeFields)                           \
     P(message)                               \
     P(microsecond)                           \

Userland/Libraries/LibJS/Runtime/Intl/LocalePrototype.cpp

@@ -41,6 +41,7 @@ void LocalePrototype::initialize(GlobalObject& global_object)
     auto& vm = this->vm();
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.maximize, maximize, 0, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
 
     // 14.3.2 Intl.Locale.prototype[ @@toStringTag ], https://tc39.es/ecma402/#sec-Intl.Locale.prototype-@@tostringtag
@@ -58,6 +59,26 @@ void LocalePrototype::initialize(GlobalObject& global_object)
     define_native_accessor(vm.names.region, region, {}, Attribute::Configurable);
 }
 
+// 14.3.3 Intl.Locale.prototype.maximize ( ), https://tc39.es/ecma402/#sec-Intl.Locale.prototype.maximize
+JS_DEFINE_NATIVE_FUNCTION(LocalePrototype::maximize)
+{
+    // 1. Let loc be the this value.
+    // 2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
+    auto* locale_object = typed_this(global_object);
+    if (!locale_object)
+        return {};
+
+    auto locale = Unicode::parse_unicode_locale_id(locale_object->locale());
+    VERIFY(locale.has_value());
+
+    // 3. Let maximal be the result of the Add Likely Subtags algorithm applied to loc.[[Locale]]. If an error is signaled, set maximal to loc.[[Locale]].
+    if (auto maximal = Unicode::add_likely_subtags(locale->language_id); maximal.has_value())
+        locale->language_id = maximal.release_value();
+
+    // 4. Return ! Construct(%Locale%, maximal).
+    return Locale::create(global_object, *locale);
+}
+
 // 14.3.5 Intl.Locale.prototype.toString ( ), https://tc39.es/ecma402/#sec-Intl.Locale.prototype.toString
 JS_DEFINE_NATIVE_FUNCTION(LocalePrototype::to_string)
 {

Userland/Libraries/LibJS/Runtime/Intl/LocalePrototype.h

@@ -19,6 +19,7 @@ public:
     virtual ~LocalePrototype() override = default;
 
 private:
+    JS_DECLARE_NATIVE_FUNCTION(maximize);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
 
     JS_DECLARE_NATIVE_GETTER(base_name);

Userland/Libraries/LibJS/Tests/builtins/Intl/Locale/Locale.prototype.maximize.js

@@ -0,0 +1,32 @@
+test("length is 0", () => {
+    expect(Intl.Locale.prototype.maximize).toHaveLength(0);
+});
+
+test("normal behavior", () => {
+    expect(new Intl.Locale("en").maximize().toString()).toBe("en-Latn-US");
+
+    expect(new Intl.Locale("en-Latn").maximize().toString()).toBe("en-Latn-US");
+    expect(new Intl.Locale("en-Shaw").maximize().toString()).toBe("en-Shaw-GB");
+    expect(new Intl.Locale("en-Arab").maximize().toString()).toBe("en-Arab-US");
+
+    expect(new Intl.Locale("en-US").maximize().toString()).toBe("en-Latn-US");
+    expect(new Intl.Locale("en-GB").maximize().toString()).toBe("en-Latn-GB");
+    expect(new Intl.Locale("en-FR").maximize().toString()).toBe("en-Latn-FR");
+
+    expect(new Intl.Locale("it-Kana-CA").maximize().toString()).toBe("it-Kana-CA");
+
+    expect(new Intl.Locale("und").maximize().toString()).toBe("en-Latn-US");
+    expect(new Intl.Locale("und-Thai").maximize().toString()).toBe("th-Thai-TH");
+    expect(new Intl.Locale("und-419").maximize().toString()).toBe("es-Latn-419");
+    expect(new Intl.Locale("und-150").maximize().toString()).toBe("ru-Cyrl-RU");
+    expect(new Intl.Locale("und-AT").maximize().toString()).toBe("de-Latn-AT");
+    expect(new Intl.Locale("und-Cyrl-RO").maximize().toString()).toBe("bg-Cyrl-RO");
+    expect(new Intl.Locale("und-AQ").maximize().toString()).toBe("und-Latn-AQ");
+});
+
+test("keywords are preserved", () => {
+    expect(new Intl.Locale("en-u-ca-abc").maximize().toString()).toBe("en-Latn-US-u-ca-abc");
+    expect(new Intl.Locale("en", { calendar: "abc" }).maximize().toString()).toBe(
+        "en-Latn-US-u-ca-abc"
+    );
+});