LibJS: Define constructor slots for describing how to read options

This is an editorial change in the ECMA-402 spec. See:
a2beb66

We implement this change by introducing a virtual interface that all
Intl "service" objects must implement. A future patch will make use of
the virtualized RelevantExtensionKeys and ResolutionOptionDescriptors
accessors, and we will need to be able to use those slots from a generic
instance type.

Libraries/LibJS/Forward.h

@@ -274,11 +274,14 @@ JS_ENUMERATE_INTL_OBJECTS
 #undef __JS_ENUMERATE
 
 class Intl;
+class IntlObject;
 class MathematicalValue;
 
 // Not included in JS_ENUMERATE_INTL_OBJECTS due to missing distinct constructor
 class Segments;
 class SegmentsPrototype;
+
+struct ResolutionOptionDescriptor;
 };
 
 namespace Temporal {

Libraries/LibJS/Runtime/Intl/Collator.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2024, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2022-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -12,7 +12,7 @@ GC_DEFINE_ALLOCATOR(Collator);
 
 // 10 Collator Objects, https://tc39.es/ecma402/#collator-objects
 Collator::Collator(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    : IntlObject(ConstructWithPrototypeTag::Tag, prototype)
 {
 }
 
@@ -22,4 +22,27 @@ void Collator::visit_edges(Visitor& visitor)
     visitor.visit(m_bound_compare);
 }
 
+// 10.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl-collator-internal-slots
+ReadonlySpan<StringView> Collator::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is a List that must include the element "co", may include any or all of the elements "kf" and "kn", and must not include any other elements.
+    static constexpr AK::Array keys { "co"sv, "kf"sv, "kn"sv };
+    return keys;
+}
+
+// 10.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl-collator-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> Collator::resolution_option_descriptors(VM& vm) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "co", [[Property]]: "collation" }, { [[Key]]: "kn", [[Property]]: "numeric", [[Type]]: boolean }, { [[Key]]: "kf", [[Property]]: "caseFirst", [[Values]]: « "upper", "lower", "false" » } ».
+    static constexpr AK::Array case_first_values { "upper"sv, "lower"sv, "false"sv };
+
+    static auto descriptors = to_array<ResolutionOptionDescriptor>({
+        { .key = "co"sv, .property = vm.names.collation },
+        { .key = "kn"sv, .property = vm.names.numeric, .type = OptionType::Boolean },
+        { .key = "kf"sv, .property = vm.names.caseFirst, .values = case_first_values },
+    });
+
+    return descriptors;
+}
+
 }

Libraries/LibJS/Runtime/Intl/Collator.h

@@ -1,34 +1,29 @@
 /*
- * Copyright (c) 2022-2024, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2022-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #pragma once
 
-#include <AK/Array.h>
 #include <AK/String.h>
 #include <AK/StringView.h>
 #include <LibJS/Runtime/Intl/CollatorCompareFunction.h>
-#include <LibJS/Runtime/Object.h>
+#include <LibJS/Runtime/Intl/IntlObject.h>
 #include <LibUnicode/Collator.h>
 
 namespace JS::Intl {
 
-class Collator final : public Object {
+class Collator final : public IntlObject {
-    JS_OBJECT(Collator, Object);
+    JS_OBJECT(Collator, IntlObject);
     GC_DECLARE_ALLOCATOR(Collator);
 
 public:
-    static constexpr auto relevant_extension_keys()
-    {
-        // 10.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl-collator-internal-slots
-        // The value of the [[RelevantExtensionKeys]] internal slot is a List that must include the element "co", may include any or all of the elements "kf" and "kn", and must not include any other elements.
-        return AK::Array { "co"sv, "kf"sv, "kn"sv };
-    }
-
     virtual ~Collator() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     String const& locale() const { return m_locale; }
     void set_locale(String locale) { m_locale = move(locale); }
 

Libraries/LibJS/Runtime/Intl/CollatorConstructor.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2024, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2022-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -113,7 +113,7 @@ ThrowCompletionOr<GC::Ref<Object>> CollatorConstructor::construct(FunctionObject
     opt.kf = locale_key_from_value(case_first);
 
     // 21. Let r be ResolveLocale(%Intl.Collator%.[[AvailableLocales]], requestedLocales, opt, %Intl.Collator%.[[RelevantExtensionKeys]], localeData).
-    auto result = resolve_locale(requested_locales, opt, Collator::relevant_extension_keys());
+    auto result = resolve_locale(requested_locales, opt, collator->relevant_extension_keys());
 
     // 22. Set collator.[[Locale]] to r.[[Locale]].
     collator->set_locale(move(result.locale));

Libraries/LibJS/Runtime/Intl/DateTimeFormat.cpp

@@ -24,7 +24,7 @@ GC_DEFINE_ALLOCATOR(DateTimeFormat);
 
 // 11 DateTimeFormat Objects, https://tc39.es/ecma402/#datetimeformat-objects
 DateTimeFormat::DateTimeFormat(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    : IntlObject(ConstructWithPrototypeTag::Tag, prototype)
 {
 }
 
@@ -34,6 +34,30 @@ void DateTimeFormat::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_bound_format);
 }
 
+// 11.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.datetimeformat-internal-slots
+ReadonlySpan<StringView> DateTimeFormat::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is « "ca", "hc", "nu" ».
+    static constexpr AK::Array keys { "ca"sv, "hc"sv, "nu"sv };
+    return keys;
+}
+
+// 11.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.datetimeformat-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> DateTimeFormat::resolution_option_descriptors(VM& vm) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "ca", [[Property]]: "calendar" }, { [[Key]]: "nu", [[Property]]: "numberingSystem" }, { [[Key]]: "hour12", [[Property]]: "hour12", [[Type]]: boolean }, { [[Key]]: "hc", [[Property]]: "hourCycle", [[Values]]: « "h11", "h12", "h23", "h24" » } ».
+    static constexpr AK::Array hour_cycle_values { "h11"sv, "h12"sv, "h23"sv, "h24"sv };
+
+    static auto descriptors = to_array<ResolutionOptionDescriptor>({
+        { .key = "ca"sv, .property = vm.names.calendar },
+        { .key = "nu"sv, .property = vm.names.numberingSystem },
+        { .key = "hour12"sv, .property = vm.names.hour12, .type = OptionType::Boolean },
+        { .key = "hc"sv, .property = vm.names.hourCycle, .values = hour_cycle_values },
+    });
+
+    return descriptors;
+}
+
 static Optional<Unicode::DateTimeFormat const&> get_or_create_formatter(StringView locale, StringView time_zone, OwnPtr<Unicode::DateTimeFormat>& formatter, Optional<Unicode::CalendarPattern> const& format)
 {
     if (formatter)

Libraries/LibJS/Runtime/Intl/DateTimeFormat.h

@@ -13,28 +13,24 @@
 #include <AK/Vector.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Intl/DateTimeFormatConstructor.h>
-#include <LibJS/Runtime/Object.h>
+#include <LibJS/Runtime/Intl/IntlObject.h>
 #include <LibJS/Runtime/VM.h>
 #include <LibUnicode/DateTimeFormat.h>
 
 namespace JS::Intl {
 
-class DateTimeFormat final : public Object {
+class DateTimeFormat final : public IntlObject {
-    JS_OBJECT(DateTimeFormat, Object);
+    JS_OBJECT(DateTimeFormat, IntlObject);
     GC_DECLARE_ALLOCATOR(DateTimeFormat);
 
     using Patterns = Unicode::CalendarPattern;
 
 public:
-    static constexpr auto relevant_extension_keys()
-    {
-        // 11.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.datetimeformat-internal-slots
-        // The value of the [[RelevantExtensionKeys]] internal slot is « "ca", "hc", "nu" ».
-        return AK::Array { "ca"sv, "hc"sv, "nu"sv };
-    }
-
     virtual ~DateTimeFormat() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     String const& locale() const { return m_locale; }
     void set_locale(String locale) { m_locale = move(locale); }
 
@@ -90,7 +86,7 @@ public:
     void set_temporal_time_zone(String temporal_time_zone) { m_temporal_time_zone = move(temporal_time_zone); }
 
 private:
-    DateTimeFormat(Object& prototype);
+    explicit DateTimeFormat(Object& prototype);
 
     virtual void visit_edges(Visitor&) override;
 

Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, Tim Flynn <trflynn89@ladybird.org>
+ * Copyright (c) 2021-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -145,7 +145,7 @@ ThrowCompletionOr<GC::Ref<DateTimeFormat>> create_date_time_format(VM& vm, Funct
     opt.hc = locale_key_from_value(hour_cycle);
 
     // 17. Let r be ResolveLocale(%Intl.DateTimeFormat%.[[AvailableLocales]], requestedLocales, opt, %Intl.DateTimeFormat%.[[RelevantExtensionKeys]], %Intl.DateTimeFormat%.[[LocaleData]]).
-    auto result = resolve_locale(requested_locales, opt, DateTimeFormat::relevant_extension_keys());
+    auto result = resolve_locale(requested_locales, opt, date_time_format->relevant_extension_keys());
 
     // 18. Set dateTimeFormat.[[Locale]] to r.[[Locale]].
     date_time_format->set_locale(move(result.locale));

Libraries/LibJS/Runtime/Intl/DisplayNames.cpp

@@ -4,9 +4,9 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Intl/AbstractOperations.h>
 #include <LibJS/Runtime/Intl/DisplayNames.h>
+#include <LibJS/Runtime/VM.h>
 
 namespace JS::Intl {
 
@@ -14,10 +14,24 @@ GC_DEFINE_ALLOCATOR(DisplayNames);
 
 // 12 DisplayNames Objects, https://tc39.es/ecma402/#intl-displaynames-objects
 DisplayNames::DisplayNames(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    : IntlObject(ConstructWithPrototypeTag::Tag, prototype)
 {
 }
 
+// 12.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.DisplayNames-internal-slots
+ReadonlySpan<StringView> DisplayNames::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is « ».
+    return {};
+}
+
+// 12.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.DisplayNames-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> DisplayNames::resolution_option_descriptors(VM&) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « ».
+    return {};
+}
+
 void DisplayNames::set_type(StringView type)
 {
     if (type == "language"sv)

Libraries/LibJS/Runtime/Intl/DisplayNames.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2021-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -9,14 +9,14 @@
 #include <AK/Optional.h>
 #include <AK/String.h>
 #include <AK/StringView.h>
-#include <LibJS/Runtime/Object.h>
+#include <LibJS/Runtime/Intl/IntlObject.h>
 #include <LibUnicode/DisplayNames.h>
 #include <LibUnicode/Locale.h>
 
 namespace JS::Intl {
 
-class DisplayNames final : public Object {
+class DisplayNames final : public IntlObject {
-    JS_OBJECT(DisplayNames, Object);
+    JS_OBJECT(DisplayNames, IntlObject);
     GC_DECLARE_ALLOCATOR(DisplayNames);
 
     enum class Type {
@@ -38,6 +38,9 @@ class DisplayNames final : public Object {
 public:
     virtual ~DisplayNames() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     String const& locale() const { return m_locale; }
     void set_locale(String locale) { m_locale = move(locale); }
 
@@ -59,7 +62,7 @@ public:
     StringView language_display_string() const { return Unicode::language_display_to_string(*m_language_display); }
 
 private:
-    DisplayNames(Object& prototype);
+    explicit DisplayNames(Object& prototype);
 
     String m_locale;                                       // [[Locale]]
     Unicode::Style m_style { Unicode::Style::Long };       // [[Style]]

Libraries/LibJS/Runtime/Intl/DisplayNamesConstructor.cpp

@@ -75,7 +75,7 @@ ThrowCompletionOr<GC::Ref<Object>> DisplayNamesConstructor::construct(FunctionOb
     opt.locale_matcher = matcher;
 
     // 9. Let r be ResolveLocale(%Intl.DisplayNames%.[[AvailableLocales]], requestedLocales, opt, %Intl.DisplayNames%.[[RelevantExtensionKeys]], %Intl.DisplayNames%.[[LocaleData]]).
-    auto result = resolve_locale(requested_locales, opt, {});
+    auto result = resolve_locale(requested_locales, opt, display_names->relevant_extension_keys());
 
     // 10. Let style be ? GetOption(options, "style", string, « "narrow", "short", "long" », "long").
     auto style = TRY(get_option(vm, *options, vm.names.style, OptionType::String, { "narrow"sv, "short"sv, "long"sv }, "long"sv));

Libraries/LibJS/Runtime/Intl/DurationFormat.cpp

@@ -8,15 +8,12 @@
 #include <AK/GenericShorthands.h>
 #include <AK/StringBuilder.h>
 #include <LibJS/Runtime/AbstractOperations.h>
-#include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Intl/DurationFormat.h>
 #include <LibJS/Runtime/Intl/ListFormat.h>
 #include <LibJS/Runtime/Intl/ListFormatConstructor.h>
 #include <LibJS/Runtime/Intl/MathematicalValue.h>
 #include <LibJS/Runtime/Intl/NumberFormatConstructor.h>
-#include <LibJS/Runtime/Intl/PluralRules.h>
+#include <LibJS/Runtime/VM.h>
-#include <LibJS/Runtime/Intl/PluralRulesConstructor.h>
-#include <LibJS/Runtime/Intl/RelativeTimeFormat.h>
 #include <LibJS/Runtime/ValueInlines.h>
 
 namespace JS::Intl {
@@ -25,10 +22,29 @@ GC_DEFINE_ALLOCATOR(DurationFormat);
 
 // 13 DurationFormat Objects, https://tc39.es/ecma402/#durationformat-objects
 DurationFormat::DurationFormat(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    : IntlObject(ConstructWithPrototypeTag::Tag, prototype)
 {
 }
 
+// 13.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.DurationFormat-internal-slots
+ReadonlySpan<StringView> DurationFormat::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
+    static constexpr AK::Array keys { "nu"sv };
+    return keys;
+}
+
+// 13.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.DurationFormat-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> DurationFormat::resolution_option_descriptors(VM& vm) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "nu", [[Property]]: "numberingSystem" } ».
+    static auto descriptors = to_array<ResolutionOptionDescriptor>({
+        { .key = "nu"sv, .property = vm.names.numberingSystem },
+    });
+
+    return descriptors;
+}
+
 DurationFormat::Style DurationFormat::style_from_string(StringView style)
 {
     if (style == "long"sv)

Libraries/LibJS/Runtime/Intl/DurationFormat.h

@@ -10,15 +10,14 @@
 #include <AK/Array.h>
 #include <AK/String.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
-#include <LibJS/Runtime/Intl/AbstractOperations.h>
+#include <LibJS/Runtime/Intl/IntlObject.h>
-#include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/Duration.h>
 #include <LibUnicode/Locale.h>
 
 namespace JS::Intl {
 
-class DurationFormat final : public Object {
+class DurationFormat final : public IntlObject {
-    JS_OBJECT(DurationFormat, Object);
+    JS_OBJECT(DurationFormat, IntlObject);
     GC_DECLARE_ALLOCATOR(DurationFormat);
 
 public:
@@ -72,15 +71,11 @@ public:
         Display display { Display::Auto };
     };
 
-    static constexpr auto relevant_extension_keys()
-    {
-        // 13.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.DurationFormat-internal-slots
-        // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
-        return AK::Array { "nu"sv };
-    }
-
     virtual ~DurationFormat() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     void set_locale(String locale) { m_locale = move(locale); }
     String const& locale() const { return m_locale; }
 

Libraries/LibJS/Runtime/Intl/DurationFormatConstructor.cpp

@@ -81,7 +81,7 @@ ThrowCompletionOr<GC::Ref<Object>> DurationFormatConstructor::construct(Function
     opt.nu = locale_key_from_value(numbering_system);
 
     // 9. Let r be ResolveLocale(%Intl.DurationFormat%.[[AvailableLocales]], requestedLocales, opt, %Intl.DurationFormat%.[[RelevantExtensionKeys]], %Intl.DurationFormat%.[[LocaleData]]).
-    auto result = resolve_locale(requested_locales, opt, DurationFormat::relevant_extension_keys());
+    auto result = resolve_locale(requested_locales, opt, duration_format->relevant_extension_keys());
 
     // 10. Set durationFormat.[[Locale]] to r.[[Locale]].
     duration_format->set_locale(move(result.locale));

Libraries/LibJS/Runtime/Intl/IntlObject.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Span.h>
+#include <AK/StringView.h>
+#include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/Object.h>
+#include <LibJS/Runtime/PropertyKey.h>
+
+namespace JS::Intl {
+
+// https://tc39.es/ecma402/#resolution-option-descriptor
+struct ResolutionOptionDescriptor {
+    StringView key;
+    PropertyKey property;
+    OptionType type { OptionType::String };
+    ReadonlySpan<StringView> values {};
+};
+
+class IntlObject : public Object {
+    JS_OBJECT(IntlObject, Object);
+
+public:
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const = 0;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const = 0;
+
+protected:
+    using Object::Object;
+};
+
+}

Libraries/LibJS/Runtime/Intl/ListFormat.cpp

@@ -4,11 +4,10 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/StringBuilder.h>
 #include <LibJS/Runtime/Array.h>
-#include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Intl/ListFormat.h>
 #include <LibJS/Runtime/Iterator.h>
+#include <LibJS/Runtime/VM.h>
 #include <LibUnicode/ListFormat.h>
 
 namespace JS::Intl {
@@ -17,10 +16,24 @@ GC_DEFINE_ALLOCATOR(ListFormat);
 
 // 14 ListFormat Objects, https://tc39.es/ecma402/#listformat-objects
 ListFormat::ListFormat(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    : IntlObject(ConstructWithPrototypeTag::Tag, prototype)
 {
 }
 
+// 14.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.ListFormat-internal-slots
+ReadonlySpan<StringView> ListFormat::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is « ».
+    return {};
+}
+
+// 14.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.ListFormat-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> ListFormat::resolution_option_descriptors(VM&) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « ».
+    return {};
+}
+
 // 14.5.2 CreatePartsFromList ( listFormat, list ), https://tc39.es/ecma402/#sec-createpartsfromlist
 Vector<Unicode::ListFormat::Partition> create_parts_from_list(ListFormat const& list_format, ReadonlySpan<String> list)
 {

Libraries/LibJS/Runtime/Intl/ListFormat.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2021-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -9,15 +9,14 @@
 #include <AK/String.h>
 #include <AK/StringView.h>
 #include <AK/Vector.h>
-#include <LibJS/Runtime/Intl/AbstractOperations.h>
+#include <LibJS/Runtime/Intl/IntlObject.h>
-#include <LibJS/Runtime/Object.h>
 #include <LibUnicode/ListFormat.h>
 #include <LibUnicode/Locale.h>
 
 namespace JS::Intl {
 
-class ListFormat final : public Object {
+class ListFormat final : public IntlObject {
-    JS_OBJECT(ListFormat, Object);
+    JS_OBJECT(ListFormat, IntlObject);
     GC_DECLARE_ALLOCATOR(ListFormat);
 
 public:
@@ -30,6 +29,9 @@ public:
 
     virtual ~ListFormat() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     String const& locale() const { return m_locale; }
     void set_locale(String locale) { m_locale = move(locale); }
 

Libraries/LibJS/Runtime/Intl/ListFormatConstructor.cpp

@@ -70,7 +70,7 @@ ThrowCompletionOr<GC::Ref<Object>> ListFormatConstructor::construct(FunctionObje
     opt.locale_matcher = matcher;
 
     // 8. Let r be ResolveLocale(%Intl.ListFormat%.[[AvailableLocales]], requestedLocales, opt, %Intl.ListFormat%.[[RelevantExtensionKeys]], %Intl.ListFormat%.[[LocaleData]]).
-    auto result = resolve_locale(requested_locales, opt, {});
+    auto result = resolve_locale(requested_locales, opt, list_format->relevant_extension_keys());
 
     // 9. Set listFormat.[[Locale]] to r.[[Locale]].
     list_format->set_locale(move(result.locale));

Libraries/LibJS/Runtime/Intl/NumberFormat.cpp

@@ -4,22 +4,15 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/Checked.h>
-#include <AK/StringBuilder.h>
-#include <AK/Utf8View.h>
 #include <LibCrypto/BigInt/SignedBigInteger.h>
-#include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/BigInt.h>
-#include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Intl/NumberFormat.h>
-#include <LibJS/Runtime/Intl/NumberFormatFunction.h>
+#include <LibJS/Runtime/NativeFunction.h>
-#include <LibJS/Runtime/Intl/PluralRules.h>
+#include <LibJS/Runtime/VM.h>
 #include <LibJS/Runtime/ValueInlines.h>
 #include <LibUnicode/CurrencyCode.h>
-#include <LibUnicode/DisplayNames.h>
 #include <math.h>
-#include <stdlib.h>
 
 namespace JS::Intl {
 
@@ -27,7 +20,7 @@ GC_DEFINE_ALLOCATOR(NumberFormatBase);
 GC_DEFINE_ALLOCATOR(NumberFormat);
 
 NumberFormatBase::NumberFormatBase(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    : IntlObject(ConstructWithPrototypeTag::Tag, prototype)
 {
 }
 
@@ -44,6 +37,25 @@ void NumberFormat::visit_edges(Cell::Visitor& visitor)
         visitor.visit(m_bound_format);
 }
 
+// 16.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.numberformat-internal-slots
+ReadonlySpan<StringView> NumberFormat::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
+    static constexpr AK::Array keys { "nu"sv };
+    return keys;
+}
+
+// 16.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.numberformat-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> NumberFormat::resolution_option_descriptors(VM& vm) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "nu", [[Property]]: "numberingSystem" } ».
+    static auto descriptors = to_array<ResolutionOptionDescriptor>({
+        { .key = "nu"sv, .property = vm.names.numberingSystem },
+    });
+
+    return descriptors;
+}
+
 StringView NumberFormatBase::computed_rounding_priority_string() const
 {
     switch (m_computed_rounding_priority) {

Libraries/LibJS/Runtime/Intl/NumberFormat.h

@@ -6,19 +6,18 @@
 
 #pragma once
 
-#include <AK/Array.h>
 #include <AK/Optional.h>
 #include <AK/String.h>
 #include <LibJS/Runtime/Intl/AbstractOperations.h>
+#include <LibJS/Runtime/Intl/IntlObject.h>
 #include <LibJS/Runtime/Intl/MathematicalValue.h>
-#include <LibJS/Runtime/Object.h>
 #include <LibUnicode/Locale.h>
 #include <LibUnicode/NumberFormat.h>
 
 namespace JS::Intl {
 
-class NumberFormatBase : public Object {
+class NumberFormatBase : public IntlObject {
-    JS_OBJECT(NumberFormatBase, Object);
+    JS_OBJECT(NumberFormatBase, IntlObject);
     GC_DECLARE_ALLOCATOR(NumberFormatBase);
 
 public:
@@ -102,15 +101,11 @@ class NumberFormat final : public NumberFormatBase {
     GC_DECLARE_ALLOCATOR(NumberFormat);
 
 public:
-    static constexpr auto relevant_extension_keys()
-    {
-        // 16.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.numberformat-internal-slots
-        // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
-        return AK::Array { "nu"sv };
-    }
-
     virtual ~NumberFormat() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     String const& numbering_system() const { return m_numbering_system; }
     void set_numbering_system(String numbering_system) { m_numbering_system = move(numbering_system); }
 

Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.cpp

@@ -83,7 +83,7 @@ ThrowCompletionOr<GC::Ref<Object>> NumberFormatConstructor::construct(FunctionOb
     opt.nu = locale_key_from_value(numbering_system);
 
     // 11. Let r be ResolveLocale(%Intl.NumberFormat%.[[AvailableLocales]], requestedLocales, opt, %Intl.NumberFormat%.[[RelevantExtensionKeys]], %Intl.NumberFormat%.[[LocaleData]]).
-    auto result = resolve_locale(requested_locales, opt, NumberFormat::relevant_extension_keys());
+    auto result = resolve_locale(requested_locales, opt, number_format->relevant_extension_keys());
 
     // 12. Set numberFormat.[[Locale]] to r.[[Locale]].
     number_format->set_locale(move(result.locale));

Libraries/LibJS/Runtime/Intl/PluralRules.cpp

@@ -17,6 +17,20 @@ PluralRules::PluralRules(Object& prototype)
 {
 }
 
+// 17.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.pluralrules-internal-slots
+ReadonlySpan<StringView> PluralRules::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is « ».
+    return {};
+}
+
+// 17.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.pluralrules-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> PluralRules::resolution_option_descriptors(VM&) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « ».
+    return {};
+}
+
 // 17.5.2 ResolvePlural ( pluralRules, n ), https://tc39.es/ecma402/#sec-resolveplural
 Unicode::PluralCategory resolve_plural(PluralRules const& plural_rules, Value number)
 {

Libraries/LibJS/Runtime/Intl/PluralRules.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2024, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2022-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -21,6 +21,9 @@ class PluralRules final : public NumberFormatBase {
 public:
     virtual ~PluralRules() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     Unicode::PluralForm type() const { return m_type; }
     StringView type_string() const { return Unicode::plural_form_to_string(m_type); }
     void set_type(StringView type) { m_type = Unicode::plural_form_from_string(type); }

Libraries/LibJS/Runtime/Intl/PluralRulesConstructor.cpp

@@ -71,7 +71,7 @@ ThrowCompletionOr<GC::Ref<Object>> PluralRulesConstructor::construct(FunctionObj
     opt.locale_matcher = matcher;
 
     // 8. Let r be ResolveLocale(%Intl.PluralRules%.[[AvailableLocales]], requestedLocales, opt, %Intl.PluralRules%.[[RelevantExtensionKeys]], %Intl.PluralRules%.[[LocaleData]]).
-    auto result = resolve_locale(requested_locales, opt, {});
+    auto result = resolve_locale(requested_locales, opt, plural_rules->relevant_extension_keys());
 
     // 9. Set pluralRules.[[Locale]] to r.[[locale]].
     plural_rules->set_locale(move(result.locale));

Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp

@@ -5,14 +5,9 @@
  */
 
 #include <AK/Enumerate.h>
-#include <AK/StringBuilder.h>
-#include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Array.h>
-#include <LibJS/Runtime/GlobalObject.h>
-#include <LibJS/Runtime/Intl/NumberFormat.h>
-#include <LibJS/Runtime/Intl/NumberFormatConstructor.h>
-#include <LibJS/Runtime/Intl/PluralRules.h>
 #include <LibJS/Runtime/Intl/RelativeTimeFormat.h>
+#include <LibJS/Runtime/VM.h>
 
 namespace JS::Intl {
 
@@ -20,10 +15,29 @@ GC_DEFINE_ALLOCATOR(RelativeTimeFormat);
 
 // 18 RelativeTimeFormat Objects, https://tc39.es/ecma402/#relativetimeformat-objects
 RelativeTimeFormat::RelativeTimeFormat(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    : IntlObject(ConstructWithPrototypeTag::Tag, prototype)
 {
 }
 
+// 18.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.RelativeTimeFormat-internal-slots
+ReadonlySpan<StringView> RelativeTimeFormat::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
+    static constexpr AK::Array keys { "nu"sv };
+    return keys;
+}
+
+// 18.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.RelativeTimeFormat-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> RelativeTimeFormat::resolution_option_descriptors(VM& vm) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "nu", [[Property]]: "numberingSystem" } ».
+    static auto descriptors = to_array<ResolutionOptionDescriptor>({
+        { .key = "nu"sv, .property = vm.names.numberingSystem },
+    });
+
+    return descriptors;
+}
+
 // 18.5.1 SingularRelativeTimeUnit ( unit ), https://tc39.es/ecma402/#sec-singularrelativetimeunit
 ThrowCompletionOr<Unicode::TimeUnit> singular_relative_time_unit(VM& vm, StringView unit)
 {

Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.h

@@ -6,32 +6,25 @@
 
 #pragma once
 
-#include <AK/Array.h>
 #include <AK/String.h>
 #include <AK/StringView.h>
 #include <LibJS/Runtime/Completion.h>
-#include <LibJS/Runtime/Intl/AbstractOperations.h>
+#include <LibJS/Runtime/Intl/IntlObject.h>
-#include <LibJS/Runtime/Object.h>
 #include <LibUnicode/Locale.h>
-#include <LibUnicode/NumberFormat.h>
 #include <LibUnicode/RelativeTimeFormat.h>
 
 namespace JS::Intl {
 
-class RelativeTimeFormat final : public Object {
+class RelativeTimeFormat final : public IntlObject {
-    JS_OBJECT(RelativeTimeFormat, Object);
+    JS_OBJECT(RelativeTimeFormat, IntlObject);
     GC_DECLARE_ALLOCATOR(RelativeTimeFormat);
 
 public:
-    static constexpr auto relevant_extension_keys()
-    {
-        // 18.2.3 Internal slots, https://tc39.es/ecma402/#sec-Intl.RelativeTimeFormat-internal-slots
-        // The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».
-        return AK::Array { "nu"sv };
-    }
-
     virtual ~RelativeTimeFormat() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     String const& locale() const { return m_locale; }
     void set_locale(String locale) { m_locale = move(locale); }
 

Libraries/LibJS/Runtime/Intl/RelativeTimeFormatConstructor.cpp

@@ -83,7 +83,7 @@ ThrowCompletionOr<GC::Ref<Object>> RelativeTimeFormatConstructor::construct(Func
     opt.nu = locale_key_from_value(numbering_system);
 
     // 11. Let r be ResolveLocale(%Intl.RelativeTimeFormat%.[[AvailableLocales]], requestedLocales, opt, %Intl.RelativeTimeFormat%.[[RelevantExtensionKeys]], %Intl.RelativeTimeFormat%.[[LocaleData]]).
-    auto result = resolve_locale(requested_locales, opt, RelativeTimeFormat::relevant_extension_keys());
+    auto result = resolve_locale(requested_locales, opt, relative_time_format->relevant_extension_keys());
 
     // 12. Let locale be r.[[Locale]].
     auto locale = move(result.locale);

Libraries/LibJS/Runtime/Intl/Segmenter.cpp

@@ -6,8 +6,8 @@
  */
 
 #include <AK/Utf16View.h>
-#include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Intl/Segmenter.h>
+#include <LibJS/Runtime/VM.h>
 
 namespace JS::Intl {
 
@@ -15,10 +15,24 @@ GC_DEFINE_ALLOCATOR(Segmenter);
 
 // 19 Segmenter Objects, https://tc39.es/ecma402/#segmenter-objects
 Segmenter::Segmenter(Object& prototype)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+    : IntlObject(ConstructWithPrototypeTag::Tag, prototype)
 {
 }
 
+// 19.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.segmenter-internal-slots
+ReadonlySpan<StringView> Segmenter::relevant_extension_keys() const
+{
+    // The value of the [[RelevantExtensionKeys]] internal slot is « ».
+    return {};
+}
+
+// 19.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl.segmenter-internal-slots
+ReadonlySpan<ResolutionOptionDescriptor> Segmenter::resolution_option_descriptors(VM&) const
+{
+    // The value of the [[ResolutionOptionDescriptors]] internal slot is « ».
+    return {};
+}
+
 // 19.7.1 CreateSegmentDataObject ( segmenter, string, startIndex, endIndex ), https://tc39.es/ecma402/#sec-createsegmentdataobject
 ThrowCompletionOr<GC::Ref<Object>> create_segment_data_object(VM& vm, Unicode::Segmenter const& segmenter, Utf16View const& string, size_t start_index, size_t end_index)
 {

Libraries/LibJS/Runtime/Intl/Segmenter.h

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2022, Idan Horowitz <idan.horowitz@serenityos.org>
- * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2023-2025, Tim Flynn <trflynn89@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -8,18 +8,21 @@
 #pragma once
 
 #include <AK/String.h>
-#include <LibJS/Runtime/Object.h>
+#include <LibJS/Runtime/Intl/IntlObject.h>
 #include <LibUnicode/Segmenter.h>
 
 namespace JS::Intl {
 
-class Segmenter final : public Object {
+class Segmenter final : public IntlObject {
-    JS_OBJECT(Segmenter, Object);
+    JS_OBJECT(Segmenter, IntlObject);
     GC_DECLARE_ALLOCATOR(Segmenter);
 
 public:
     virtual ~Segmenter() override = default;
 
+    virtual ReadonlySpan<StringView> relevant_extension_keys() const override;
+    virtual ReadonlySpan<ResolutionOptionDescriptor> resolution_option_descriptors(VM&) const override;
+
     String const& locale() const { return m_locale; }
     void set_locale(String locale) { m_locale = move(locale); }
 

Libraries/LibJS/Runtime/Intl/SegmenterConstructor.cpp

@@ -71,7 +71,7 @@ ThrowCompletionOr<GC::Ref<Object>> SegmenterConstructor::construct(FunctionObjec
     opt.locale_matcher = matcher;
 
     // 9. Let r be ResolveLocale(%Intl.Segmenter%.[[AvailableLocales]], requestedLocales, opt, %Intl.Segmenter%.[[RelevantExtensionKeys]], %Intl.Segmenter%.[[LocaleData]]).
-    auto result = resolve_locale(requested_locales, opt, {});
+    auto result = resolve_locale(requested_locales, opt, segmenter->relevant_extension_keys());
 
     // 10. Set segmenter.[[Locale]] to r.[[locale]].
     segmenter->set_locale(move(result.locale));