LibJS: Implement Intl.DisplayNames.supportedLocalesOf()

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -403,6 +403,7 @@ namespace JS {
     P(substring)                             \
     P(subtract)                              \
     P(sup)                                   \
+    P(supportedLocalesOf)                    \
     P(tan)                                   \
     P(tanh)                                  \
     P(test)                                  \

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

@@ -7,6 +7,7 @@
 #include <AK/AllOf.h>
 #include <AK/AnyOf.h>
 #include <AK/CharacterTypes.h>
+#include <AK/Function.h>
 #include <AK/QuickSort.h>
 #include <AK/TypeCasts.h>
 #include <LibJS/Runtime/Array.h>
@@ -402,6 +403,77 @@ LocaleResult resolve_locale(Vector<String> const& requested_locales, LocaleOptio
     return result;
 }
 
+// 9.2.8 LookupSupportedLocales ( availableLocales, requestedLocales ), https://tc39.es/ecma402/#sec-lookupsupportedlocales
+Vector<String> lookup_supported_locales(Vector<String> const& requested_locales)
+{
+    // 1. Let subset be a new empty List.
+    Vector<String> subset;
+
+    // 2. For each element locale of requestedLocales, do
+    for (auto const& locale : requested_locales) {
+        auto locale_id = Unicode::parse_unicode_locale_id(locale);
+        VERIFY(locale_id.has_value());
+
+        // a. Let noExtensionsLocale be the String value that is locale with any Unicode locale extension sequences removed.
+        locale_id->remove_extension_type<Unicode::LocaleExtension>();
+        auto no_extensions_locale = locale_id->to_string();
+
+        // b. Let availableLocale be BestAvailableLocale(availableLocales, noExtensionsLocale).
+        auto available_locale = best_available_locale(no_extensions_locale);
+
+        // c. If availableLocale is not undefined, append locale to the end of subset.
+        if (available_locale.has_value())
+            subset.append(locale);
+    }
+
+    // 3. Return subset.
+    return subset;
+}
+
+// 9.2.9 BestFitSupportedLocales ( availableLocales, requestedLocales ), https://tc39.es/ecma402/#sec-bestfitsupportedlocales
+Vector<String> best_fit_supported_locales(Vector<String> const& requested_locales)
+{
+    // The BestFitSupportedLocales abstract operation returns the subset of the provided BCP 47
+    // language priority list requestedLocales for which availableLocales has a matching locale
+    // when using the Best Fit Matcher algorithm. Locales appear in the same order in the returned
+    // list as in requestedLocales. The steps taken are implementation dependent.
+
+    // :yakbrain:
+    return lookup_supported_locales(requested_locales);
+}
+
+// 9.2.10 SupportedLocales ( availableLocales, requestedLocales, options ), https://tc39.es/ecma402/#sec-supportedlocales
+Array* supported_locales(GlobalObject& global_object, Vector<String> const& requested_locales, Value options)
+{
+    auto& vm = global_object.vm();
+
+    // 1. Set options to ? CoerceOptionsToObject(options).
+    auto* options_object = coerce_options_to_object(global_object, options);
+    if (vm.exception())
+        return {};
+
+    // 2. Let matcher be ? GetOption(options, "localeMatcher", "string", « "lookup", "best fit" », "best fit").
+    auto matcher = get_option(global_object, options_object, vm.names.localeMatcher, Value::Type::String, { "lookup"sv, "best fit"sv }, "best fit"sv);
+    if (vm.exception())
+        return {};
+
+    Vector<String> supported_locales;
+
+    // 3. If matcher is "best fit", then
+    if (matcher.as_string().string() == "best fit"sv) {
+        // a. Let supportedLocales be BestFitSupportedLocales(availableLocales, requestedLocales).
+        supported_locales = best_fit_supported_locales(requested_locales);
+    }
+    // 4. Else,
+    else {
+        // a. Let supportedLocales be LookupSupportedLocales(availableLocales, requestedLocales).
+        supported_locales = lookup_supported_locales(requested_locales);
+    }
+
+    // 5. Return CreateArrayFromList(supportedLocales).
+    return Array::create_from<String>(global_object, supported_locales, [&vm](auto& locale) { return js_string(vm, locale); });
+}
+
 // 9.2.12 CoerceOptionsToObject ( options ), https://tc39.es/ecma402/#sec-coerceoptionstoobject
 Object* coerce_options_to_object(GlobalObject& global_object, Value options)
 {

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

@@ -29,6 +29,9 @@ struct LocaleResult {
 Optional<Unicode::LocaleID> is_structurally_valid_language_tag(StringView locale);
 String canonicalize_unicode_locale_id(Unicode::LocaleID& locale);
 Vector<String> canonicalize_locale_list(GlobalObject&, Value locales);
+Vector<String> best_fit_supported_locales(Vector<String> const& requested_locales);
+Vector<String> lookup_supported_locales(Vector<String> const& requested_locales);
+Array* supported_locales(GlobalObject&, Vector<String> const& requested_locales, Value options);
 Object* coerce_options_to_object(GlobalObject& global_object, Value options);
 Value get_option(GlobalObject& global_object, Value options, PropertyName const& property, Value::Type type, Vector<StringView> const& values, Fallback fallback);
 String insert_unicode_extension_and_canonicalize(Unicode::LocaleID locale_id, Unicode::LocaleExtension extension);

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

@@ -5,6 +5,7 @@
  */
 
 #include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Intl/AbstractOperations.h>
 #include <LibJS/Runtime/Intl/DisplayNames.h>
@@ -28,6 +29,10 @@ void DisplayNamesConstructor::initialize(GlobalObject& global_object)
 
     // 12.3.1 Intl.DisplayNames.prototype, https://tc39.es/ecma402/#sec-Intl.DisplayNames.prototype
     define_direct_property(vm.names.prototype, global_object.intl_display_names_prototype(), 0);
+
+    u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.supportedLocalesOf, supported_locales_of, 1, attr);
+
     define_direct_property(vm.names.length, Value(2), Attribute::Configurable);
 }
 
@@ -125,4 +130,22 @@ Value DisplayNamesConstructor::construct(FunctionObject& new_target)
     return display_names;
 }
 
+// 12.3.2 Intl.DisplayNames.supportedLocalesOf ( locales [ , options ] ), https://tc39.es/ecma402/#sec-Intl.DisplayNames.supportedLocalesOf
+JS_DEFINE_NATIVE_FUNCTION(DisplayNamesConstructor::supported_locales_of)
+{
+    auto locales = vm.argument(0);
+    auto options = vm.argument(1);
+
+    // 1. Let availableLocales be %DisplayNames%.[[AvailableLocales]].
+    // No-op, availability of each requested locale is checked via Unicode::is_locale_available()
+
+    // 2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
+    auto requested_locales = canonicalize_locale_list(global_object, locales);
+    if (vm.exception())
+        return {};
+
+    // 3. Return ? SupportedLocales(availableLocales, requestedLocales, options).
+    return supported_locales(global_object, requested_locales, options);
+}
+
 }

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

@@ -23,6 +23,8 @@ public:
 
 private:
     virtual bool has_constructor() const override { return true; }
+
+    JS_DECLARE_NATIVE_FUNCTION(supported_locales_of);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Intl/DisplayNames/DisplayNames.supportedLocalesOf.js

@@ -0,0 +1,43 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Intl.DisplayNames.supportedLocalesOf).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        // prettier-ignore
+        const values = [
+            [[], []],
+            [undefined, []],
+            ["en", ["en"]],
+            [new Intl.Locale("en"), ["en"]],
+            [["en"], ["en"]],
+            [["en", "en-gb", "en-us"], ["en", "en-GB", "en-US"]],
+            [["en", "de", "fr"], ["en", "de", "fr"]],
+            [["en-foobar"], ["en-foobar"]],
+            [["en-foobar-u-abc"], ["en-foobar-u-abc"]],
+            [["aa", "zz"], []],
+            [["en", "aa", "zz"], ["en"]],
+        ];
+        for (const [input, expected] of values) {
+            expect(Intl.DisplayNames.supportedLocalesOf(input)).toEqual(expected);
+            // "best fit" (implementation defined) just uses the same implementation as "lookup" at the moment
+            expect(
+                Intl.DisplayNames.supportedLocalesOf(input, { localeMatcher: "best fit" })
+            ).toEqual(Intl.DisplayNames.supportedLocalesOf(input, { localeMatcher: "lookup" }));
+        }
+    });
+});
+
+describe("errors", () => {
+    test("invalid value for localeMatcher option", () => {
+        expect(() => {
+            Intl.DisplayNames.supportedLocalesOf([], { localeMatcher: "foo" });
+        }).toThrowWithMessage(RangeError, "foo is not a valid value for option localeMatcher");
+    });
+
+    test("invalid language tag", () => {
+        expect(() => {
+            Intl.DisplayNames.supportedLocalesOf(["aaaaaaaaa"]);
+        }).toThrowWithMessage(RangeError, "aaaaaaaaa is not a structurally valid language tag");
+    });
+});