LibJS+LibUnicode: Fully implement Intl.Collator with ICU

We were never able to implement anything other than a basic, locale-
unaware collator with the JSON export of the CLDR as it did not have
collation data. We can now use ICU to implement collation.

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2022-2024, Tim Flynn <trflynn89@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -16,83 +16,6 @@ Collator::Collator(Object& prototype)
 {
 }
 
-void Collator::set_usage(StringView type)
-{
-    if (type == "sort"sv)
-        m_usage = Usage::Sort;
-    else if (type == "search"sv)
-        m_usage = Usage::Search;
-    else
-        VERIFY_NOT_REACHED();
-}
-
-StringView Collator::usage_string() const
-{
-    switch (m_usage) {
-    case Usage::Sort:
-        return "sort"sv;
-    case Usage::Search:
-        return "search"sv;
-    default:
-        VERIFY_NOT_REACHED();
-    }
-}
-
-void Collator::set_sensitivity(StringView type)
-{
-    if (type == "base"sv)
-        m_sensitivity = Sensitivity::Base;
-    else if (type == "accent"sv)
-        m_sensitivity = Sensitivity::Accent;
-    else if (type == "case"sv)
-        m_sensitivity = Sensitivity::Case;
-    else if (type == "variant"sv)
-        m_sensitivity = Sensitivity::Variant;
-    else
-        VERIFY_NOT_REACHED();
-}
-
-StringView Collator::sensitivity_string() const
-{
-    switch (m_sensitivity) {
-    case Sensitivity::Base:
-        return "base"sv;
-    case Sensitivity::Accent:
-        return "accent"sv;
-    case Sensitivity::Case:
-        return "case"sv;
-    case Sensitivity::Variant:
-        return "variant"sv;
-    default:
-        VERIFY_NOT_REACHED();
-    }
-}
-
-void Collator::set_case_first(StringView case_first)
-{
-    if (case_first == "upper"sv)
-        m_case_first = CaseFirst::Upper;
-    else if (case_first == "lower"sv)
-        m_case_first = CaseFirst::Lower;
-    else if (case_first == "false"sv)
-        m_case_first = CaseFirst::False;
-    else
-        VERIFY_NOT_REACHED();
-}
-
-StringView Collator::case_first_string() const
-{
-    switch (m_case_first) {
-    case CaseFirst::Upper:
-        return "upper"sv;
-    case CaseFirst::Lower:
-        return "lower"sv;
-    case CaseFirst::False:
-        return "false"sv;
-    default:
-        VERIFY_NOT_REACHED();
-    }
-}
 void Collator::visit_edges(Visitor& visitor)
 {
     Base::visit_edges(visitor);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2022-2024, Tim Flynn <trflynn89@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -11,6 +11,7 @@
 #include <AK/StringView.h>
 #include <LibJS/Runtime/Intl/CollatorCompareFunction.h>
 #include <LibJS/Runtime/Object.h>
+#include <LibUnicode/Collator.h>
 
 namespace JS::Intl {
 
@@ -19,24 +20,6 @@ class Collator final : public Object {
     JS_DECLARE_ALLOCATOR(Collator);
 
 public:
-    enum class Usage {
-        Sort,
-        Search,
-    };
-
-    enum class Sensitivity {
-        Base,
-        Accent,
-        Case,
-        Variant,
-    };
-
-    enum class CaseFirst {
-        Upper,
-        Lower,
-        False,
-    };
-
     static constexpr auto relevant_extension_keys()
     {
         // 10.2.3 Internal slots, https://tc39.es/ecma402/#sec-intl-collator-internal-slots
@@ -49,17 +32,17 @@ public:
     String const& locale() const { return m_locale; }
     void set_locale(String locale) { m_locale = move(locale); }
 
-    Usage usage() const { return m_usage; }
-    void set_usage(StringView usage);
-    StringView usage_string() const;
+    Unicode::Usage usage() const { return m_usage; }
+    void set_usage(StringView usage) { m_usage = Unicode::usage_from_string(usage); }
+    StringView usage_string() const { return Unicode::usage_to_string(m_usage); }
 
-    Sensitivity sensitivity() const { return m_sensitivity; }
-    void set_sensitivity(StringView sensitivity);
-    StringView sensitivity_string() const;
+    Unicode::Sensitivity sensitivity() const { return m_sensitivity; }
+    void set_sensitivity(StringView sensitivity) { m_sensitivity = Unicode::sensitivity_from_string(sensitivity); }
+    StringView sensitivity_string() const { return Unicode::sensitivity_to_string(m_sensitivity); }
 
-    CaseFirst case_first() const { return m_case_first; }
-    void set_case_first(StringView case_first);
-    StringView case_first_string() const;
+    Unicode::CaseFirst case_first() const { return m_case_first; }
+    void set_case_first(StringView case_first) { m_case_first = Unicode::case_first_from_string(case_first); }
+    StringView case_first_string() const { return Unicode::case_first_to_string(m_case_first); }
 
     String const& collation() const { return m_collation; }
     void set_collation(String collation) { m_collation = move(collation); }
@@ -73,19 +56,25 @@ public:
     CollatorCompareFunction* bound_compare() const { return m_bound_compare; }
     void set_bound_compare(CollatorCompareFunction* bound_compare) { m_bound_compare = bound_compare; }
 
+    Unicode::Collator const& collator() const { return *m_collator; }
+    void set_collator(NonnullOwnPtr<Unicode::Collator> collator) { m_collator = move(collator); }
+
 private:
     explicit Collator(Object& prototype);
 
     virtual void visit_edges(Visitor&) override;
 
-    String m_locale;                                    // [[Locale]]
-    Usage m_usage { Usage::Sort };                      // [[Usage]]
-    Sensitivity m_sensitivity { Sensitivity::Variant }; // [[Sensitivity]]
-    CaseFirst m_case_first { CaseFirst::False };        // [[CaseFirst]]
-    String m_collation;                                 // [[Collation]]
-    bool m_ignore_punctuation { false };                // [[IgnorePunctuation]]
-    bool m_numeric { false };                           // [[Numeric]]
-    GCPtr<CollatorCompareFunction> m_bound_compare;     // [[BoundCompare]]
+    String m_locale;                                                      // [[Locale]]
+    Unicode::Usage m_usage { Unicode::Usage::Sort };                      // [[Usage]]
+    Unicode::Sensitivity m_sensitivity { Unicode::Sensitivity::Variant }; // [[Sensitivity]]
+    Unicode::CaseFirst m_case_first { Unicode::CaseFirst::False };        // [[CaseFirst]]
+    String m_collation;                                                   // [[Collation]]
+    bool m_ignore_punctuation { false };                                  // [[IgnorePunctuation]]
+    bool m_numeric { false };                                             // [[Numeric]]
+    GCPtr<CollatorCompareFunction> m_bound_compare;                       // [[BoundCompare]]
+
+    // Non-standard. Stores the ICU collator for the Intl object's collation options.
+    OwnPtr<Unicode::Collator> m_collator;
 };
 
 }

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

@@ -31,22 +31,10 @@ void CollatorCompareFunction::initialize(Realm&)
     define_direct_property(vm.names.name, PrimitiveString::create(vm, String {}), Attribute::Configurable);
 }
 
-// 10.3.3.2 CompareStrings ( collator, x, y ), https://tc39.es/ecma402/#sec-collator-comparestrings
-double compare_strings(Collator& collator, Utf8View const& x, Utf8View const& y)
+void CollatorCompareFunction::visit_edges(Visitor& visitor)
 {
-    // FIXME: Implement https://unicode.org/reports/tr10
-    (void)collator;
-    auto x_iterator = x.begin();
-    auto y_iterator = y.begin();
-    for (; x_iterator != x.end() && y_iterator != y.end(); ++x_iterator, ++y_iterator) {
-        if (*x_iterator != *y_iterator)
-            return static_cast<double>(*x_iterator) - static_cast<double>(*y_iterator);
-    }
-    if (x_iterator != x.end())
-        return 1.0;
-    if (y_iterator != y.end())
-        return -1.0;
-    return 0.0;
+    Base::visit_edges(visitor);
+    visitor.visit(m_collator);
 }
 
 // 10.3.3.1 Collator Compare Functions, https://tc39.es/ecma402/#sec-collator-compare-functions
@@ -61,17 +49,32 @@ ThrowCompletionOr<Value> CollatorCompareFunction::call()
 
     // 5. Let X be ? ToString(x).
     auto x = TRY(vm.argument(0).to_string(vm));
+
     // 6. Let Y be ? ToString(y).
     auto y = TRY(vm.argument(1).to_string(vm));
 
     // 7. Return CompareStrings(collator, X, Y).
-    return compare_strings(m_collator, x.code_points(), y.code_points());
+    return compare_strings(m_collator, x, y);
 }
 
-void CollatorCompareFunction::visit_edges(Visitor& visitor)
+// 10.3.3.2 CompareStrings ( collator, x, y ), https://tc39.es/ecma402/#sec-collator-comparestrings
+int compare_strings(Collator const& collator, StringView x, StringView y)
 {
-    Base::visit_edges(visitor);
-    visitor.visit(m_collator);
+    auto result = collator.collator().compare(x, y);
+
+    // The result is intended to correspond with a sort order of String values according to the effective locale and
+    // collation options of collator, and will be negative when x is ordered before y, positive when x is ordered after
+    // y, and zero in all other cases (representing no relative ordering between x and y).
+    switch (result) {
+    case Unicode::Collator::Order::Before:
+        return -1;
+    case Unicode::Collator::Order::Equal:
+        return 0;
+    case Unicode::Collator::Order::After:
+        return 1;
+    }
+
+    VERIFY_NOT_REACHED();
 }
 
 }

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

@@ -30,6 +30,6 @@ private:
     NonnullGCPtr<Collator> m_collator; // [[Collator]]
 };
 
-double compare_strings(Collator&, Utf8View const& x, Utf8View const& y);
+int compare_strings(Collator const&, StringView x, StringView y);
 
 }

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

@@ -114,7 +114,7 @@ static ThrowCompletionOr<NonnullGCPtr<Collator>> initialize_collator(VM& vm, Col
     // 27. If sensitivity is undefined, then
     if (sensitivity.is_undefined()) {
         // a. If usage is "sort", then
-        if (collator.usage() == Collator::Usage::Sort) {
+        if (collator.usage() == Unicode::Usage::Sort) {
             // i. Let sensitivity be "variant".
             sensitivity = PrimitiveString::create(vm, "variant"_string);
         }
@@ -136,6 +136,17 @@ static ThrowCompletionOr<NonnullGCPtr<Collator>> initialize_collator(VM& vm, Col
     // 30. Set collator.[[IgnorePunctuation]] to ignorePunctuation.
     collator.set_ignore_punctuation(ignore_punctuation.as_bool());
 
+    // Non-standard, create an ICU collator for this Intl object.
+    auto icu_collator = Unicode::Collator::create(
+        collator.locale(),
+        collator.usage(),
+        collator.collation(),
+        collator.sensitivity(),
+        collator.case_first(),
+        collator.numeric(),
+        collator.ignore_punctuation());
+    collator.set_collator(move(icu_collator));
+
     // 31. Return collator.
     return collator;
 }

Userland/Libraries/LibJS/Runtime/StringPrototype.cpp

@@ -566,7 +566,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::locale_compare)
     auto collator = TRY(construct(vm, realm.intrinsics().intl_collator_constructor(), vm.argument(1), vm.argument(2)));
 
     // 5. Return CompareStrings(collator, S, thatValue).
-    return Intl::compare_strings(static_cast<Intl::Collator&>(*collator), string.code_points(), that_value.code_points());
+    return Intl::compare_strings(static_cast<Intl::Collator const&>(*collator), string, that_value);
 }
 
 // 22.1.3.13 String.prototype.match ( regexp ), https://tc39.es/ecma262/#sec-string.prototype.match

Userland/Libraries/LibJS/Tests/builtins/Intl/Collator/Collator.prototype.compare.js

@@ -17,13 +17,13 @@ describe("correct behavior", () => {
             const aTob = collator.compare(a, b);
             const bToa = collator.compare(b, a);
 
-            expect(aTob > 0).toBeTrue();
-            expect(aTob).toBe(-bToa);
+            expect(aTob).toBe(1);
+            expect(bToa).toBe(-1);
         }
 
         compareBoth("a", "");
         compareBoth("1", "");
-        compareBoth("a", "A");
+        compareBoth("A", "a");
         compareBoth("7", "3");
         compareBoth("0000", "0");
 
@@ -31,8 +31,65 @@ describe("correct behavior", () => {
         expect(collator.compare("undefined", undefined)).toBe(0);
 
         expect(collator.compare("null", null)).toBe(0);
-        expect(collator.compare("null", undefined)).not.toBe(0);
-        expect(collator.compare("null") < 0).toBeTrue();
+        expect(collator.compare("null", undefined)).toBe(-1);
+        expect(collator.compare("null")).toBe(-1);
+    });
+
+    test("canonically equivalent strings", () => {
+        var tests = [
+            ["ä\u0306", "a\u0308\u0306"],
+            ["ă\u0308", "a\u0306\u0308"],
+            ["ạ\u0308", "a\u0323\u0308"],
+            ["a\u0308\u0323", "a\u0323\u0308"],
+            ["ä\u0323", "a\u0323\u0308"],
+            ["Å", "Å"],
+            ["Å", "A\u030A"],
+            ["Ç", "C\u0327"],
+            ["ḋ\u0323", "ḍ\u0307"],
+            ["ḋ\u0323", "d\u0323\u0307"],
+            ["ô", "o\u0302"],
+            ["ö", "o\u0308"],
+            ["q\u0307\u0323", "q\u0323\u0307"],
+            ["ṩ", "s\u0323\u0307"],
+            ["ự", "ụ\u031B"],
+            ["ự", "u\u031B\u0323"],
+            ["ự", "ư\u0323"],
+            ["ự", "u\u0323\u031B"],
+            ["Ω", "Ω"],
+            ["x\u031B\u0323", "x\u0323\u031B"],
+            ["퓛", "\u1111\u1171\u11B6"],
+            ["北", "\uD87E\uDC2B"],
+            ["가", "\u1100\u1161"],
+            ["\uD834\uDD5E", "\uD834\uDD57\uD834\uDD65"],
+        ];
+
+        const en = new Intl.Collator("en");
+        const ja = new Intl.Collator("ja");
+        const th = new Intl.Collator("th");
+
+        tests.forEach(test => {
+            expect(en.compare(test[0], test[1])).toBe(0);
+            expect(ja.compare(test[0], test[1])).toBe(0);
+            expect(th.compare(test[0], test[1])).toBe(0);
+        });
+    });
+
+    test("ignorePunctuation", () => {
+        [undefined, true, false].forEach(ignorePunctuation => {
+            let expected = false;
+
+            const en = new Intl.Collator("en", { ignorePunctuation });
+            expect(en.compare("", " ")).toBe(en.resolvedOptions().ignorePunctuation ? 0 : -1);
+            expect(en.compare("", ",")).toBe(en.resolvedOptions().ignorePunctuation ? 0 : -1);
+
+            const ja = new Intl.Collator("ja", { ignorePunctuation });
+            expect(ja.compare("", " ")).toBe(ja.resolvedOptions().ignorePunctuation ? 0 : -1);
+            expect(ja.compare("", ",")).toBe(ja.resolvedOptions().ignorePunctuation ? 0 : -1);
+
+            const th = new Intl.Collator("th", { ignorePunctuation });
+            expect(th.compare("", " ")).toBe(th.resolvedOptions().ignorePunctuation ? 0 : -1);
+            expect(th.compare("", ",")).toBe(th.resolvedOptions().ignorePunctuation ? 0 : -1);
+        });
     });
 
     test("UTF-16", () => {

Userland/Libraries/LibJS/Tests/builtins/String/String.prototype.localeCompare.js

@@ -15,7 +15,7 @@ test("basic functionality", () => {
 
     compareBoth("a", "");
     compareBoth("1", "");
-    compareBoth("a", "A");
+    compareBoth("A", "a");
     compareBoth("7", "3");
     compareBoth("0000", "0");
 

Userland/Libraries/LibUnicode/CMakeLists.txt

@@ -2,6 +2,7 @@ include(${SerenityOS_SOURCE_DIR}/Meta/CMake/unicode_data.cmake)
 
 set(SOURCES
     CharacterTypes.cpp
+    Collator.cpp
     CurrencyCode.cpp
     DateTimeFormat.cpp
     DisplayNames.cpp

Userland/Libraries/LibUnicode/Collator.cpp

@@ -0,0 +1,196 @@
+/*
+ * Copyright (c) 2024, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibUnicode/Collator.h>
+#include <LibUnicode/ICU.h>
+
+#include <unicode/coll.h>
+
+namespace Unicode {
+
+Usage usage_from_string(StringView usage)
+{
+    if (usage == "sort"sv)
+        return Usage::Sort;
+    if (usage == "search"sv)
+        return Usage::Search;
+    VERIFY_NOT_REACHED();
+}
+
+StringView usage_to_string(Usage usage)
+{
+    switch (usage) {
+    case Usage::Sort:
+        return "sort"sv;
+    case Usage::Search:
+        return "search"sv;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+static NonnullOwnPtr<icu::Locale> apply_usage_to_locale(icu::Locale const& locale, Usage usage, StringView collation)
+{
+    auto result = adopt_own(*locale.clone());
+    UErrorCode status = U_ZERO_ERROR;
+
+    switch (usage) {
+    case Usage::Sort:
+        result->setUnicodeKeywordValue("co", icu_string_piece(collation), status);
+        break;
+    case Usage::Search:
+        result->setUnicodeKeywordValue("co", "search", status);
+        break;
+    }
+
+    VERIFY(icu_success(status));
+    return result;
+}
+
+Sensitivity sensitivity_from_string(StringView sensitivity)
+{
+    if (sensitivity == "base"sv)
+        return Sensitivity::Base;
+    if (sensitivity == "accent"sv)
+        return Sensitivity::Accent;
+    if (sensitivity == "case"sv)
+        return Sensitivity::Case;
+    if (sensitivity == "variant"sv)
+        return Sensitivity::Variant;
+    VERIFY_NOT_REACHED();
+}
+
+StringView sensitivity_to_string(Sensitivity sensitivity)
+{
+    switch (sensitivity) {
+    case Sensitivity::Base:
+        return "base"sv;
+    case Sensitivity::Accent:
+        return "accent"sv;
+    case Sensitivity::Case:
+        return "case"sv;
+    case Sensitivity::Variant:
+        return "variant"sv;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+static constexpr UColAttributeValue icu_sensitivity(Sensitivity sensitivity)
+{
+    switch (sensitivity) {
+    case Sensitivity::Base:
+        return UCOL_PRIMARY;
+    case Sensitivity::Accent:
+        return UCOL_SECONDARY;
+    case Sensitivity::Case:
+        return UCOL_PRIMARY;
+    case Sensitivity::Variant:
+        return UCOL_TERTIARY;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+CaseFirst case_first_from_string(StringView case_first)
+{
+    if (case_first == "upper"sv)
+        return CaseFirst::Upper;
+    if (case_first == "lower"sv)
+        return CaseFirst::Lower;
+    if (case_first == "false"sv)
+        return CaseFirst::False;
+    VERIFY_NOT_REACHED();
+}
+
+StringView case_first_to_string(CaseFirst case_first)
+{
+    switch (case_first) {
+    case CaseFirst::Upper:
+        return "upper"sv;
+    case CaseFirst::Lower:
+        return "lower"sv;
+    case CaseFirst::False:
+        return "false"sv;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+static constexpr UColAttributeValue icu_case_first(CaseFirst case_first)
+{
+    switch (case_first) {
+    case CaseFirst::Upper:
+        return UCOL_UPPER_FIRST;
+    case CaseFirst::Lower:
+        return UCOL_LOWER_FIRST;
+    case CaseFirst::False:
+        return UCOL_OFF;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+class CollatorImpl : public Collator {
+public:
+    explicit CollatorImpl(NonnullOwnPtr<icu::Collator> collator)
+        : m_collator(move(collator))
+    {
+    }
+
+    virtual Collator::Order compare(StringView lhs, StringView rhs) const override
+    {
+        UErrorCode status = U_ZERO_ERROR;
+
+        auto result = m_collator->compareUTF8(icu_string_piece(lhs), icu_string_piece(rhs), status);
+        VERIFY(icu_success(status));
+
+        switch (result) {
+        case UCOL_LESS:
+            return Order::Before;
+        case UCOL_EQUAL:
+            return Order::Equal;
+        case UCOL_GREATER:
+            return Order::After;
+        }
+
+        VERIFY_NOT_REACHED();
+    }
+
+private:
+    NonnullOwnPtr<icu::Collator> m_collator;
+};
+
+NonnullOwnPtr<Collator> Collator::create(
+    StringView locale,
+    Usage usage,
+    StringView collation,
+    Sensitivity sensitivity,
+    CaseFirst case_first,
+    bool numeric,
+    bool ignore_punctuation)
+{
+    UErrorCode status = U_ZERO_ERROR;
+
+    auto locale_data = LocaleData::for_locale(locale);
+    VERIFY(locale_data.has_value());
+
+    auto locale_with_usage = apply_usage_to_locale(locale_data->locale(), usage, collation);
+
+    auto collator = adopt_own(*icu::Collator::createInstance(*locale_with_usage, status));
+    VERIFY(icu_success(status));
+
+    auto set_attribute = [&](UColAttribute attribute, UColAttributeValue value) {
+        collator->setAttribute(attribute, value, status);
+        VERIFY(icu_success(status));
+    };
+
+    set_attribute(UCOL_STRENGTH, icu_sensitivity(sensitivity));
+    set_attribute(UCOL_CASE_LEVEL, sensitivity == Sensitivity::Case ? UCOL_ON : UCOL_OFF);
+    set_attribute(UCOL_CASE_FIRST, icu_case_first(case_first));
+    set_attribute(UCOL_NUMERIC_COLLATION, numeric ? UCOL_ON : UCOL_OFF);
+    set_attribute(UCOL_ALTERNATE_HANDLING, ignore_punctuation ? UCOL_SHIFTED : UCOL_NON_IGNORABLE);
+    set_attribute(UCOL_NORMALIZATION_MODE, UCOL_ON);
+
+    return adopt_own(*new CollatorImpl(move(collator)));
+}
+
+}

Userland/Libraries/LibUnicode/Collator.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2024, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullOwnPtr.h>
+#include <AK/StringView.h>
+
+namespace Unicode {
+
+enum class Usage {
+    Sort,
+    Search,
+};
+Usage usage_from_string(StringView);
+StringView usage_to_string(Usage);
+
+enum class Sensitivity {
+    Base,
+    Accent,
+    Case,
+    Variant,
+};
+Sensitivity sensitivity_from_string(StringView);
+StringView sensitivity_to_string(Sensitivity);
+
+enum class CaseFirst {
+    Upper,
+    Lower,
+    False,
+};
+CaseFirst case_first_from_string(StringView);
+StringView case_first_to_string(CaseFirst);
+
+class Collator {
+public:
+    static NonnullOwnPtr<Collator> create(
+        StringView locale,
+        Usage,
+        StringView collation,
+        Sensitivity,
+        CaseFirst,
+        bool numeric,
+        bool ignore_punctuation);
+
+    virtual ~Collator() = default;
+
+    enum class Order {
+        Before,
+        Equal,
+        After,
+    };
+    virtual Order compare(StringView, StringView) const = 0;
+
+protected:
+    Collator() = default;
+};
+
+}