LibJS: Allow "approximately" results to differ in plural form

This is a normative change in the Intl.NumberFormat V3 spec. See:
https://github.com/tc39/proposal-intl-numberformat-v3/commit/08f599b

Note that this didn't seem to actually affect our implementation. The
Unicode spec states:

https://www.unicode.org/reports/tr35/tr35-53/tr35-numbers.html#Plural_Ranges
"If there is no value for a <start,end> pair, the default result is end"

Therefore, our implementation did not have the behavior noted by the
issue this normative change addressed:

    const pr = new Intl.PluralRules("en-US");
    pr.selectRange(1, 1); // Is "other", should be "one"

Our implementation already returned "one" here because there is no such
<start=one, end=one> value in the CLDR for en-US. Thus, we already
returned the end value of "one".

6 files changed, 36 insertions, 17 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp b/Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp
index b31f316497..07e826d538 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/NumberFormat.cpp
@@ -1313,7 +1313,7 @@ ThrowCompletionOr<Optional<Variant<StringView, String>>> get_number_format_patte
         auto formats = ::Locale::get_unit_formats(number_format.data_locale(), number_format.unit(), number_format.unit_display());
         auto plurality = MUST_OR_THROW_OOM(resolve_plural(vm, number_format, ::Locale::PluralForm::Cardinal, number.to_value(vm)));
 
-        if (auto it = formats.find_if([&](auto& p) { return p.plurality == plurality; }); it != formats.end())
+        if (auto it = formats.find_if([&](auto& p) { return p.plurality == plurality.plural_category; }); it != formats.end())
             patterns = move(*it);
 
         break;
@@ -1336,7 +1336,7 @@ ThrowCompletionOr<Optional<Variant<StringView, String>>> get_number_format_patte
             auto formats = TRY_OR_THROW_OOM(vm, ::Locale::get_compact_number_system_formats(number_format.data_locale(), number_format.numbering_system(), ::Locale::CompactNumberFormatType::CurrencyUnit));
             auto plurality = MUST_OR_THROW_OOM(resolve_plural(vm, number_format, ::Locale::PluralForm::Cardinal, number.to_value(vm)));
 
-            if (auto it = formats.find_if([&](auto& p) { return p.plurality == plurality; }); it != formats.end()) {
+            if (auto it = formats.find_if([&](auto& p) { return p.plurality == plurality.plural_category; }); it != formats.end()) {
                 patterns = move(*it);
                 break;
             }
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/PluralRules.cpp b/Userland/Libraries/LibJS/Runtime/Intl/PluralRules.cpp
index 8f8527c5cc..ca4e0ce2e9 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/PluralRules.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/PluralRules.cpp
@@ -92,13 +92,14 @@ PluralRules::PluralRules(Object& prototype)
 }
 
 // 16.5.3 ResolvePlural ( pluralRules, n ), https://tc39.es/ecma402/#sec-resolveplural
-ThrowCompletionOr<::Locale::PluralCategory> resolve_plural(VM& vm, PluralRules const& plural_rules, Value number)
+// 1.5.3 ResolvePlural ( pluralRules, n ), https://tc39.es/proposal-intl-numberformat-v3/out/pluralrules/proposed.html#sec-resolveplural
+ThrowCompletionOr<ResolvedPlurality> resolve_plural(VM& vm, PluralRules const& plural_rules, Value number)
 {
     return resolve_plural(vm, plural_rules, plural_rules.type(), number);
 }
 
 // Non-standard overload of ResolvePlural to allow using the AO without an Intl.PluralRules object.
-ThrowCompletionOr<::Locale::PluralCategory> resolve_plural(VM& vm, NumberFormatBase const& number_format, ::Locale::PluralForm type, Value number)
+ThrowCompletionOr<ResolvedPlurality> resolve_plural(VM& vm, NumberFormatBase const& number_format, ::Locale::PluralForm type, Value number)
 {
     // 1. Assert: Type(pluralRules) is Object.
     // 2. Assert: pluralRules has an [[InitializedPluralRules]] internal slot.
@@ -107,7 +108,7 @@ ThrowCompletionOr<::Locale::PluralCategory> resolve_plural(VM& vm, NumberFormatB
     // 4. If n is not a finite Number, then
     if (!number.is_finite_number()) {
         // a. Return "other".
-        return ::Locale::PluralCategory::Other;
+        return ResolvedPlurality { ::Locale::PluralCategory::Other, String {} };
     }
 
     // 5. Let locale be pluralRules.[[Locale]].
@@ -119,13 +120,16 @@ ThrowCompletionOr<::Locale::PluralCategory> resolve_plural(VM& vm, NumberFormatB
     auto result = MUST_OR_THROW_OOM(format_numeric_to_string(vm, number_format, number));
 
     // 8. Let s be res.[[FormattedString]].
-    auto const& string = result.formatted_string;
+    auto string = move(result.formatted_string);
 
     // 9. Let operands be ! GetOperands(s).
     auto operands = get_operands(string);
 
-    // 10. Return ! PluralRuleSelect(locale, type, n, operands).
-    return plural_rule_select(locale, type, number, move(operands));
+    // 10. Let p be ! PluralRuleSelect(locale, type, n, operands).
+    auto plural_category = plural_rule_select(locale, type, number, move(operands));
+
+    // 11. Return the Record { [[PluralCategory]]: p, [[FormattedString]]: s }.
+    return ResolvedPlurality { plural_category, move(string) };
 }
 
 // 1.5.4 PluralRuleSelectRange ( locale, type, xp, yp ), https://tc39.es/proposal-intl-numberformat-v3/out/pluralrules/proposed.html#sec-pluralruleselectrange
@@ -154,14 +158,20 @@ ThrowCompletionOr<::Locale::PluralCategory> resolve_plural_range(VM& vm, PluralR
     // 7. Let yp be ! ResolvePlural(pluralRules, y).
     auto end_plurality = MUST_OR_THROW_OOM(resolve_plural(vm, plural_rules, end));
 
-    // 8. Let locale be pluralRules.[[Locale]].
+    // 8. If xp.[[FormattedString]] is yp.[[FormattedString]], then
+    if (start_plurality.formatted_string == end_plurality.formatted_string) {
+        // a. Return xp.[[PluralCategory]].
+        return start_plurality.plural_category;
+    }
+
+    // 9. Let locale be pluralRules.[[Locale]].
     auto const& locale = plural_rules.locale();
 
-    // 9. Let type be pluralRules.[[Type]].
+    // 10. Let type be pluralRules.[[Type]].
     auto type = plural_rules.type();
 
-    // 10. Return ! PluralRuleSelectRange(locale, type, xp, yp).
-    return plural_rule_select_range(locale, type, start_plurality, end_plurality);
+    // 11. Return ! PluralRuleSelectRange(locale, type, xp.[[PluralCategory]], yp.[[PluralCategory]]).
+    return plural_rule_select_range(locale, type, start_plurality.plural_category, end_plurality.plural_category);
 }
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/PluralRules.h b/Userland/Libraries/LibJS/Runtime/Intl/PluralRules.h
index 98300b388a..102ce2da36 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/PluralRules.h
+++ b/Userland/Libraries/LibJS/Runtime/Intl/PluralRules.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/String.h>
 #include <AK/StringView.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Intl/NumberFormat.h>
@@ -30,10 +31,15 @@ private:
     ::Locale::PluralForm m_type { ::Locale::PluralForm::Cardinal }; // [[Type]]
 };
 
+struct ResolvedPlurality {
+    ::Locale::PluralCategory plural_category; // [[PluralCategory]]
+    String formatted_string;                  // [[FormattedString]]
+};
+
 ::Locale::PluralOperands get_operands(StringView string);
 ::Locale::PluralCategory plural_rule_select(StringView locale, ::Locale::PluralForm type, Value number, ::Locale::PluralOperands operands);
-ThrowCompletionOr<::Locale::PluralCategory> resolve_plural(VM&, PluralRules const&, Value number);
-ThrowCompletionOr<::Locale::PluralCategory> resolve_plural(VM&, NumberFormatBase const& number_format, ::Locale::PluralForm type, Value number);
+ThrowCompletionOr<ResolvedPlurality> resolve_plural(VM&, PluralRules const&, Value number);
+ThrowCompletionOr<ResolvedPlurality> resolve_plural(VM&, NumberFormatBase const& number_format, ::Locale::PluralForm type, Value number);
 ::Locale::PluralCategory plural_rule_select_range(StringView locale, ::Locale::PluralForm, ::Locale::PluralCategory start, ::Locale::PluralCategory end);
 ThrowCompletionOr<::Locale::PluralCategory> resolve_plural_range(VM&, PluralRules const&, Value start, Value end);
 
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/PluralRulesPrototype.cpp b/Userland/Libraries/LibJS/Runtime/Intl/PluralRulesPrototype.cpp
index 317f0ecdb5..6b8953a8fa 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/PluralRulesPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/PluralRulesPrototype.cpp
@@ -36,6 +36,7 @@ ThrowCompletionOr<void> PluralRulesPrototype::initialize(Realm& realm)
 }
 
 // 16.3.3 Intl.PluralRules.prototype.select ( value ), https://tc39.es/ecma402/#sec-intl.pluralrules.prototype.select
+// 1.3.3 Intl.PluralRules.prototype.select ( value ), https://tc39.es/proposal-intl-numberformat-v3/out/pluralrules/proposed.html#sec-intl.pluralrules.prototype.select
 JS_DEFINE_NATIVE_FUNCTION(PluralRulesPrototype::select)
 {
     // 1. Let pr be the this value.
@@ -45,9 +46,9 @@ JS_DEFINE_NATIVE_FUNCTION(PluralRulesPrototype::select)
     // 3. Let n be ? ToNumber(value).
     auto number = TRY(vm.argument(0).to_number(vm));
 
-    // 4. Return ! ResolvePlural(pr, n).
+    // 4. Return ! ResolvePlural(pr, n).[[PluralCategory]].
     auto plurality = MUST_OR_THROW_OOM(resolve_plural(vm, *plural_rules, number));
-    return PrimitiveString::create(vm, ::Locale::plural_category_to_string(plurality));
+    return PrimitiveString::create(vm, ::Locale::plural_category_to_string(plurality.plural_category));
 }
 
 // 1.3.4 Intl.PluralRules.prototype.selectRange ( start, end ), https://tc39.es/proposal-intl-numberformat-v3/out/pluralrules/proposed.html#sec-intl.pluralrules.prototype.selectrange
diff --git a/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp b/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp
index 0b84d09756..ccf636c947 100644
--- a/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Intl/RelativeTimeFormat.cpp
@@ -181,7 +181,7 @@ ThrowCompletionOr<Vector<PatternPartitionWithUnit>> partition_relative_time_patt
     auto plurality = MUST_OR_THROW_OOM(resolve_plural(vm, relative_time_format.plural_rules(), Value(value)));
 
     // 22. Let pattern be po.[[<pr>]].
-    auto pattern = patterns.find_if([&](auto& p) { return p.plurality == plurality; });
+    auto pattern = patterns.find_if([&](auto& p) { return p.plurality == plurality.plural_category; });
     if (pattern == patterns.end())
         return Vector<PatternPartitionWithUnit> {};
 
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Intl/PluralRules/PluralRules.prototype.selectRange.js b/Userland/Libraries/LibJS/Tests/builtins/Intl/PluralRules/PluralRules.prototype.selectRange.js
index 716fbd7f5a..76619fafa6 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Intl/PluralRules/PluralRules.prototype.selectRange.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Intl/PluralRules/PluralRules.prototype.selectRange.js
@@ -39,11 +39,13 @@ describe("errors", () => {
 describe("correct behavior", () => {
     test("basic functionality", () => {
         const en = new Intl.PluralRules("en");
+        expect(en.selectRange(1, 1)).toBe("one"); // one + one = one
         expect(en.selectRange(1, 2)).toBe("other"); // one + other = other
         expect(en.selectRange(0, 1)).toBe("other"); // other + one = other
         expect(en.selectRange(2, 3)).toBe("other"); // other + other = other
 
         const pl = new Intl.PluralRules("pl");
+        expect(pl.selectRange(1, 1)).toBe("one"); // one + one = one
         expect(pl.selectRange(1, 2)).toBe("few"); // one + few = few
         expect(pl.selectRange(1, 5)).toBe("many"); // one + many = many
         expect(pl.selectRange(1, 3.14)).toBe("other"); // one + other = other