LibJS+LibLocale: Replace number range formatting with ICU

This uses ICU for the Intl.NumberFormat `formatRange` and
`formatRangeToParts` prototypes.

Note: All of the changes to the test files in this patch are now aligned
with both Chrome and Safari.

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

@@ -229,7 +229,7 @@ ThrowCompletionOr<MathematicalValue> to_intl_mathematical_value(VM& vm, Value va
 }
 
 // 15.5.19 PartitionNumberRangePattern ( numberFormat, x, y ), https://tc39.es/ecma402/#sec-partitionnumberrangepattern
-ThrowCompletionOr<Vector<PatternPartitionWithSource>> partition_number_range_pattern(VM& vm, NumberFormat& number_format, MathematicalValue start, MathematicalValue end)
+ThrowCompletionOr<Vector<::Locale::NumberFormat::Partition>> partition_number_range_pattern(VM& vm, NumberFormat const& number_format, MathematicalValue const& start, MathematicalValue const& end)
 {
     // 1. If x is NaN or y is NaN, throw a RangeError exception.
     if (start.is_nan())
@@ -237,132 +237,38 @@ ThrowCompletionOr<Vector<PatternPartitionWithSource>> partition_number_range_pat
     if (end.is_nan())
         return vm.throw_completion<RangeError>(ErrorType::NumberIsNaN, "end"sv);
 
-    // 2. Let result be a new empty List.
-    Vector<PatternPartitionWithSource> result;
-
-    // 3. Let xResult be ? PartitionNumberPattern(numberFormat, x).
-    auto raw_start_result = partition_number_pattern(number_format, start);
-    auto start_result = PatternPartitionWithSource::create_from_parent_list(move(raw_start_result));
-
-    // 4. Let yResult be ? PartitionNumberPattern(numberFormat, y).
-    auto raw_end_result = partition_number_pattern(number_format, end);
-    auto end_result = PatternPartitionWithSource::create_from_parent_list(move(raw_end_result));
-
-    // 5. If ! FormatNumeric(numberFormat, x) is equal to ! FormatNumeric(numberFormat, y), then
-    auto formatted_start = format_numeric(number_format, start);
-    auto formatted_end = format_numeric(number_format, end);
-
-    if (formatted_start == formatted_end) {
-        // a. Let appxResult be ? FormatApproximately(numberFormat, xResult).
-        auto approximate_result = format_approximately(number_format, move(start_result));
-
-        // b. For each r in appxResult, do
-        for (auto& result : approximate_result) {
-            // i. Set r.[[Source]] to "shared".
-            result.source = "shared"sv;
-        }
-
-        // c. Return appxResult.
-        return approximate_result;
-    }
-
-    // 6. For each element r in xResult, do
-    result.ensure_capacity(start_result.size());
-
-    for (auto& start_part : start_result) {
-        // a. Append a new Record { [[Type]]: r.[[Type]], [[Value]]: r.[[Value]], [[Source]]: "startRange" } as the last element of result.
-        PatternPartitionWithSource part;
-        part.type = start_part.type;
-        part.value = move(start_part.value);
-        part.source = "startRange"sv;
-
-        result.unchecked_append(move(part));
-    }
-
-    // 7. Let rangeSeparator be an ILND String value used to separate two numbers.
-    auto range_separator_symbol = ::Locale::get_number_system_symbol(number_format.data_locale(), number_format.numbering_system(), ::Locale::NumericSymbol::RangeSeparator).value_or("-"sv);
-    auto range_separator = ::Locale::augment_range_pattern(range_separator_symbol, result.last().value, end_result[0].value);
-
-    // 8. Append a new Record { [[Type]]: "literal", [[Value]]: rangeSeparator, [[Source]]: "shared" } element to result.
-    PatternPartitionWithSource part;
-    part.type = "literal"sv;
-    part.value = range_separator.has_value()
-        ? range_separator.release_value()
-        : MUST(String::from_utf8(range_separator_symbol));
-    part.source = "shared"sv;
-    result.append(move(part));
-
-    // 9. For each element r in yResult, do
-    result.ensure_capacity(result.size() + end_result.size());
-
-    for (auto& end_part : end_result) {
-        // a. Append a new Record { [[Type]]: r.[[Type]], [[Value]]: r.[[Value]], [[Source]]: "endRange" } as the last element of result.
-        PatternPartitionWithSource part;
-        part.type = end_part.type;
-        part.value = move(end_part.value);
-        part.source = "endRange"sv;
-
-        result.unchecked_append(move(part));
-    }
-
-    // 10. Return ! CollapseNumberRange(result).
-    return collapse_number_range(move(result));
-}
-
-// 15.5.20 FormatApproximately ( numberFormat, result ), https://tc39.es/ecma402/#sec-formatapproximately
-Vector<PatternPartitionWithSource> format_approximately(NumberFormat& number_format, Vector<PatternPartitionWithSource> result)
-{
-    // 1. Let approximatelySign be an ILND String value used to signify that a number is approximate.
-    auto approximately_sign = ::Locale::get_number_system_symbol(number_format.data_locale(), number_format.numbering_system(), ::Locale::NumericSymbol::ApproximatelySign);
-
-    // 2. If approximatelySign is not empty, insert a new Record { [[Type]]: "approximatelySign", [[Value]]: approximatelySign } at an ILND index in result. For example, if numberFormat has [[Locale]] "en-US" and [[NumberingSystem]] "latn" and [[Style]] "decimal", the new Record might be inserted before the first element of result.
-    if (approximately_sign.has_value() && !approximately_sign->is_empty()) {
-        PatternPartitionWithSource partition;
-        partition.type = "approximatelySign"sv;
-        partition.value = MUST(String::from_utf8(*approximately_sign));
-
-        result.insert_before_matching(move(partition), [](auto const& part) {
-            return part.type.is_one_of("integer"sv, "decimal"sv, "plusSign"sv, "minusSign"sv, "percentSign"sv, "currency"sv);
-        });
-    }
-
-    // 3. Return result.
-    return result;
-}
-
-// 15.5.21 CollapseNumberRange ( result ), https://tc39.es/ecma402/#sec-collapsenumberrange
-Vector<PatternPartitionWithSource> collapse_number_range(Vector<PatternPartitionWithSource> result)
-{
-    // Returning result unmodified is guaranteed to be a correct implementation of CollapseNumberRange.
-    return result;
+    return number_format.formatter().format_range_to_parts(start.to_value(), end.to_value());
 }
 
 // 15.5.22 FormatNumericRange ( numberFormat, x, y ), https://tc39.es/ecma402/#sec-formatnumericrange
-ThrowCompletionOr<String> format_numeric_range(VM& vm, NumberFormat& number_format, MathematicalValue start, MathematicalValue end)
+ThrowCompletionOr<String> format_numeric_range(VM& vm, NumberFormat const& number_format, MathematicalValue const& start, MathematicalValue const& end)
 {
     // 1. Let parts be ? PartitionNumberRangePattern(numberFormat, x, y).
-    auto parts = TRY(partition_number_range_pattern(vm, number_format, move(start), move(end)));
+    {
+        // NOTE: We short-circuit PartitionNumberRangePattern as we do not need individual partitions. But we must still
+        //       perform the NaN sanity checks from its first step.
 
-    // 2. Let result be the empty String.
-    StringBuilder result;
-
-    // 3. For each part in parts, do
-    for (auto& part : parts) {
-        // a. Set result to the string-concatenation of result and part.[[Value]].
-        result.append(part.value);
+        // 1. If x is NaN or y is NaN, throw a RangeError exception.
+        if (start.is_nan())
+            return vm.throw_completion<RangeError>(ErrorType::NumberIsNaN, "start"sv);
+        if (end.is_nan())
+            return vm.throw_completion<RangeError>(ErrorType::NumberIsNaN, "end"sv);
     }
 
+    // 2. Let result be the empty String.
+    // 3. For each part in parts, do
+    //     a. Set result to the string-concatenation of result and part.[[Value]].
     // 4. Return result.
-    return MUST(result.to_string());
+    return number_format.formatter().format_range(start.to_value(), end.to_value());
 }
 
 // 15.5.23 FormatNumericRangeToParts ( numberFormat, x, y ), https://tc39.es/ecma402/#sec-formatnumericrangetoparts
-ThrowCompletionOr<NonnullGCPtr<Array>> format_numeric_range_to_parts(VM& vm, NumberFormat& number_format, MathematicalValue start, MathematicalValue end)
+ThrowCompletionOr<NonnullGCPtr<Array>> format_numeric_range_to_parts(VM& vm, NumberFormat const& number_format, MathematicalValue const& start, MathematicalValue const& end)
 {
     auto& realm = *vm.current_realm();
 
     // 1. Let parts be ? PartitionNumberRangePattern(numberFormat, x, y).
-    auto parts = TRY(partition_number_range_pattern(vm, number_format, move(start), move(end)));
+    auto parts = TRY(partition_number_range_pattern(vm, number_format, start, end));
 
     // 2. Let result be ! ArrayCreate(0).
     auto result = MUST(Array::create(realm, 0));

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

@@ -194,10 +194,8 @@ Vector<::Locale::NumberFormat::Partition> partition_number_pattern(NumberFormat
 String format_numeric(NumberFormat const&, MathematicalValue const& number);
 NonnullGCPtr<Array> format_numeric_to_parts(VM&, NumberFormat const&, MathematicalValue const& number);
 ThrowCompletionOr<MathematicalValue> to_intl_mathematical_value(VM&, Value value);
-ThrowCompletionOr<Vector<PatternPartitionWithSource>> partition_number_range_pattern(VM&, NumberFormat&, MathematicalValue start, MathematicalValue end);
-Vector<PatternPartitionWithSource> format_approximately(NumberFormat&, Vector<PatternPartitionWithSource> result);
-Vector<PatternPartitionWithSource> collapse_number_range(Vector<PatternPartitionWithSource> result);
-ThrowCompletionOr<String> format_numeric_range(VM&, NumberFormat&, MathematicalValue start, MathematicalValue end);
-ThrowCompletionOr<NonnullGCPtr<Array>> format_numeric_range_to_parts(VM&, NumberFormat&, MathematicalValue start, MathematicalValue end);
+ThrowCompletionOr<Vector<::Locale::NumberFormat::Partition>> partition_number_range_pattern(VM&, NumberFormat const&, MathematicalValue const& start, MathematicalValue const& end);
+ThrowCompletionOr<String> format_numeric_range(VM&, NumberFormat const&, MathematicalValue const& start, MathematicalValue const& end);
+ThrowCompletionOr<NonnullGCPtr<Array>> format_numeric_range_to_parts(VM&, NumberFormat const&, MathematicalValue const& start, MathematicalValue const& end);
 
 }

Userland/Libraries/LibJS/Tests/builtins/Intl/NumberFormat/NumberFormat.prototype.formatRange.js

@@ -41,12 +41,12 @@ describe("correct behavior", () => {
         const en1 = new Intl.NumberFormat("en");
         expect(en1.formatRange(100, 101)).toBe("100–101");
         expect(en1.formatRange(3.14, 6.28)).toBe("3.14–6.28");
-        expect(en1.formatRange(-0, 1)).toBe("-0–1");
+        expect(en1.formatRange(-0, 1)).toBe("-0 – 1");
 
         const ja1 = new Intl.NumberFormat("ja");
         expect(ja1.formatRange(100, 101)).toBe("100～101");
         expect(ja1.formatRange(3.14, 6.28)).toBe("3.14～6.28");
-        expect(ja1.formatRange(-0, 1)).toBe("-0～1");
+        expect(ja1.formatRange(-0, 1)).toBe("-0 ～ 1");
     });
 
     test("approximately formatting", () => {
@@ -79,7 +79,7 @@ describe("correct behavior", () => {
         const en1 = new Intl.NumberFormat("en");
         expect(en1.formatRange(3, 5)).toBe("3–5");
         expect(en1.formatRange(-1, -0)).toBe("-1 – -0");
-        expect(en1.formatRange(0, Infinity)).toBe("0 – ∞");
+        expect(en1.formatRange(0, Infinity)).toBe("0–∞");
         expect(en1.formatRange(-Infinity, 0)).toBe("-∞ – 0");
 
         const en2 = new Intl.NumberFormat("en", {
@@ -92,7 +92,7 @@ describe("correct behavior", () => {
         const ja1 = new Intl.NumberFormat("ja");
         expect(ja1.formatRange(3, 5)).toBe("3～5");
         expect(ja1.formatRange(-1, -0)).toBe("-1 ～ -0");
-        expect(ja1.formatRange(0, Infinity)).toBe("0 ～ ∞");
+        expect(ja1.formatRange(0, Infinity)).toBe("0～∞");
         expect(ja1.formatRange(-Infinity, 0)).toBe("-∞ ～ 0");
 
         const ja2 = new Intl.NumberFormat("ja", {
@@ -106,21 +106,21 @@ describe("correct behavior", () => {
     test("numbers in reverse order", () => {
         const en = new Intl.NumberFormat("en");
         expect(en.formatRange(1, 0)).toBe("1–0");
-        expect(en.formatRange(1, -Infinity)).toBe("1 – -∞");
-        expect(en.formatRange(1, -0)).toBe("1 – -0");
-        expect(en.formatRange(Infinity, 0)).toBe("∞ – 0");
-        expect(en.formatRange(Infinity, -Infinity)).toBe("∞ – -∞");
-        expect(en.formatRange(Infinity, -0)).toBe("∞ – -0");
+        expect(en.formatRange(1, -Infinity)).toBe("1–-∞");
+        expect(en.formatRange(1, -0)).toBe("1–-0");
+        expect(en.formatRange(Infinity, 0)).toBe("∞–0");
+        expect(en.formatRange(Infinity, -Infinity)).toBe("∞–-∞");
+        expect(en.formatRange(Infinity, -0)).toBe("∞–-0");
         expect(en.formatRange(-0, -1)).toBe("-0 – -1");
         expect(en.formatRange(-0, -Infinity)).toBe("-0 – -∞");
 
         const ja = new Intl.NumberFormat("ja");
         expect(ja.formatRange(1, 0)).toBe("1～0");
-        expect(ja.formatRange(1, -Infinity)).toBe("1 ～ -∞");
-        expect(ja.formatRange(1, -0)).toBe("1 ～ -0");
-        expect(ja.formatRange(Infinity, 0)).toBe("∞ ～ 0");
-        expect(ja.formatRange(Infinity, -Infinity)).toBe("∞ ～ -∞");
-        expect(ja.formatRange(Infinity, -0)).toBe("∞ ～ -0");
+        expect(ja.formatRange(1, -Infinity)).toBe("1～-∞");
+        expect(ja.formatRange(1, -0)).toBe("1～-0");
+        expect(ja.formatRange(Infinity, 0)).toBe("∞～0");
+        expect(ja.formatRange(Infinity, -Infinity)).toBe("∞～-∞");
+        expect(ja.formatRange(Infinity, -0)).toBe("∞～-0");
         expect(ja.formatRange(-0, -1)).toBe("-0 ～ -1");
         expect(ja.formatRange(-0, -Infinity)).toBe("-0 ～ -∞");
     });

Userland/Libraries/LibJS/Tests/builtins/Intl/NumberFormat/NumberFormat.prototype.formatRangeToParts.js

@@ -135,13 +135,13 @@ describe("correct behavior", () => {
         const en = new Intl.NumberFormat("en");
         expect(en.formatRangeToParts(1, -Infinity)).toEqual([
             { type: "integer", value: "1", source: "startRange" },
-            { type: "literal", value: " – ", source: "shared" },
+            { type: "literal", value: "–", source: "shared" },
             { type: "minusSign", value: "-", source: "endRange" },
             { type: "infinity", value: "∞", source: "endRange" },
         ]);
         expect(en.formatRangeToParts(Infinity, -Infinity)).toEqual([
             { type: "infinity", value: "∞", source: "startRange" },
-            { type: "literal", value: " – ", source: "shared" },
+            { type: "literal", value: "–", source: "shared" },
             { type: "minusSign", value: "-", source: "endRange" },
             { type: "infinity", value: "∞", source: "endRange" },
         ]);
@@ -156,13 +156,13 @@ describe("correct behavior", () => {
         const ja = new Intl.NumberFormat("ja");
         expect(ja.formatRangeToParts(1, -Infinity)).toEqual([
             { type: "integer", value: "1", source: "startRange" },
-            { type: "literal", value: " ～ ", source: "shared" },
+            { type: "literal", value: "～", source: "shared" },
             { type: "minusSign", value: "-", source: "endRange" },
             { type: "infinity", value: "∞", source: "endRange" },
         ]);
         expect(ja.formatRangeToParts(Infinity, -Infinity)).toEqual([
             { type: "infinity", value: "∞", source: "startRange" },
-            { type: "literal", value: " ～ ", source: "shared" },
+            { type: "literal", value: "～", source: "shared" },
             { type: "minusSign", value: "-", source: "endRange" },
             { type: "infinity", value: "∞", source: "endRange" },
         ]);

Userland/Libraries/LibLocale/NumberFormat.cpp

@@ -16,10 +16,7 @@
 #include <math.h>
 
 #include <unicode/numberformatter.h>
-
-#if ENABLE_UNICODE_DATA
-#    include <LibUnicode/UnicodeData.h>
-#endif
+#include <unicode/numberrangeformatter.h>
 
 namespace Locale {
 
@@ -534,6 +531,11 @@ static constexpr StringView icu_number_format_field_to_string(i32 field, NumberF
 }
 
 struct Range {
+    constexpr bool contains(i32 position) const
+    {
+        return start <= position && position < end;
+    }
+
     constexpr bool operator<(Range const& other) const
     {
         if (start < other.start)
@@ -604,8 +606,9 @@ static void flatten_partitions(Vector<Range>& partitions)
 
 class NumberFormatImpl : public NumberFormat {
 public:
-    NumberFormatImpl(icu::number::LocalizedNumberFormatter formatter, bool is_unit)
-        : m_formatter(move(formatter))
+    NumberFormatImpl(icu::Locale& locale, icu::number::LocalizedNumberFormatter formatter, bool is_unit)
+        : m_locale(locale)
+        , m_formatter(move(formatter))
         , m_is_unit(is_unit)
     {
     }
@@ -648,10 +651,46 @@ public:
         if (!formatted.has_value())
             return {};
 
-        return format_to_parts_impl(formatted, value);
+        return format_to_parts_impl(formatted, value, value);
+    }
+
+    virtual String format_range(Value const& start, Value const& end) const override
+    {
+        UErrorCode status = U_ZERO_ERROR;
+
+        auto formatted = format_range_impl(start, end);
+        if (!formatted.has_value())
+            return {};
+
+        auto result = formatted->toTempString(status);
+        if (icu_failure(status))
+            return {};
+
+        return icu_string_to_string(result);
+    }
+
+    virtual Vector<Partition> format_range_to_parts(Value const& start, Value const& end) const override
+    {
+        auto formatted = format_range_impl(start, end);
+        if (!formatted.has_value())
+            return {};
+
+        return format_to_parts_impl(formatted, start, end);
     }
 
 private:
+    static icu::Formattable value_to_formattable(Value const& value)
+    {
+        UErrorCode status = U_ZERO_ERROR;
+
+        auto formattable = value.visit(
+            [&](double number) { return icu::Formattable { number }; },
+            [&](String const& number) { return icu::Formattable(icu_string_piece(number), status); });
+        VERIFY(icu_success(status));
+
+        return formattable;
+    }
+
     Optional<icu::number::FormattedNumber> format_impl(Value const& value) const
     {
         UErrorCode status = U_ZERO_ERROR;
@@ -670,8 +709,34 @@ private:
         return formatted;
     }
 
+    Optional<icu::number::FormattedNumberRange> format_range_impl(Value const& start, Value const& end) const
+    {
+        UErrorCode status = U_ZERO_ERROR;
+
+        if (!m_range_formatter.has_value()) {
+            auto skeleton = icu::number::NumberFormatter::forSkeleton(m_formatter.toSkeleton(status), status);
+            if (icu_failure(status))
+                return {};
+
+            auto formatter = icu::number::UnlocalizedNumberRangeFormatter().numberFormatterBoth(move(skeleton)).locale(m_locale);
+            if (icu_failure(status))
+                return {};
+
+            m_range_formatter = move(formatter);
+        }
+
+        auto formattable_start = value_to_formattable(start);
+        auto formattable_end = value_to_formattable(end);
+
+        auto formatted = m_range_formatter->formatFormattableRange(formattable_start, formattable_end, status);
+        if (icu_failure(status))
+            return {};
+
+        return formatted;
+    }
+
     template<typename Formatted>
-    Vector<Partition> format_to_parts_impl(Formatted const& formatted, Value const& value) const
+    Vector<Partition> format_to_parts_impl(Formatted const& formatted, Value const& start, Value const& end) const
     {
         UErrorCode status = U_ZERO_ERROR;
 
@@ -683,22 +748,48 @@ private:
         ranges.empend(LITERAL_FIELD, 0, formatted_number.length());
 
         icu::ConstrainedFieldPosition position;
+        Optional<Range> start_range;
+        Optional<Range> end_range;
 
         while (static_cast<bool>(formatted->nextPosition(position, status)) && icu_success(status)) {
-            ranges.empend(position.getField(), position.getStart(), position.getLimit());
+            if (position.getCategory() == UFIELD_CATEGORY_NUMBER_RANGE_SPAN) {
+                if (position.getField() == 0)
+                    start_range.emplace(position.getField(), position.getStart(), position.getLimit());
+                else
+                    end_range.emplace(position.getField(), position.getStart(), position.getLimit());
+            } else {
+                ranges.empend(position.getField(), position.getStart(), position.getLimit());
+            }
         }
 
         flatten_partitions(ranges);
 
+        auto apply_to_partition = [&](Partition& partition, auto field, auto index) {
+            if (start_range.has_value() && start_range->contains(index)) {
+                partition.type = icu_number_format_field_to_string(field, start, m_is_unit);
+                partition.source = "startRange"sv;
+                return;
+            }
+
+            if (end_range.has_value() && end_range->contains(index)) {
+                partition.type = icu_number_format_field_to_string(field, end, m_is_unit);
+                partition.source = "endRange"sv;
+                return;
+            }
+
+            partition.type = icu_number_format_field_to_string(field, end, m_is_unit);
+            partition.source = "shared"sv;
+        };
+
         Vector<Partition> result;
         result.ensure_capacity(ranges.size());
 
         for (auto const& range : ranges) {
-            auto string = formatted_number.tempSubStringBetween(range.start, range.end);
+            auto value = formatted_number.tempSubStringBetween(range.start, range.end);
 
             Partition partition;
-            partition.type = icu_number_format_field_to_string(range.field, value, m_is_unit);
-            partition.value = icu_string_to_string(string);
+            partition.value = icu_string_to_string(value);
+            apply_to_partition(partition, range.field, range.start);
 
             result.unchecked_append(move(partition));
         }
@@ -706,7 +797,9 @@ private:
         return result;
     }
 
+    icu::Locale& m_locale;
     icu::number::LocalizedNumberFormatter m_formatter;
+    mutable Optional<icu::number::LocalizedNumberRangeFormatter> m_range_formatter;
     bool m_is_unit { false };
 };
 
@@ -731,7 +824,7 @@ NonnullOwnPtr<NumberFormat> NumberFormat::create(
     }
 
     bool is_unit = display_options.style == NumberFormatStyle::Unit;
-    return adopt_own(*new NumberFormatImpl(move(formatter), is_unit));
+    return adopt_own(*new NumberFormatImpl(locale_data->locale(), move(formatter), is_unit));
 }
 
 Optional<StringView> __attribute__((weak)) get_number_system_symbol(StringView, StringView, NumericSymbol) { return {}; }
@@ -764,50 +857,4 @@ String replace_digits_for_number_system(StringView system, StringView number)
     return MUST(builder.to_string());
 }
 
-#if ENABLE_UNICODE_DATA
-static u32 last_code_point(StringView string)
-{
-    Utf8View utf8_string { string };
-    u32 code_point = 0;
-
-    for (auto it = utf8_string.begin(); it != utf8_string.end(); ++it)
-        code_point = *it;
-
-    return code_point;
-}
-#endif
-
-// https://unicode.org/reports/tr35/tr35-numbers.html#83-range-pattern-processing
-Optional<String> augment_range_pattern([[maybe_unused]] StringView range_separator, [[maybe_unused]] StringView lower, [[maybe_unused]] StringView upper)
-{
-#if ENABLE_UNICODE_DATA
-    auto range_pattern_with_spacing = [&]() {
-        return MUST(String::formatted(" {} ", range_separator));
-    };
-
-    Utf8View utf8_range_separator { range_separator };
-    Utf8View utf8_upper { upper };
-
-    // NOTE: Our implementation does the prescribed checks backwards for simplicity.
-
-    // To determine whether to add spacing, the currently recommended heuristic is:
-    // 2. If the range pattern does not contain a character having the White_Space binary Unicode property after the {0} or before the {1} placeholders.
-    for (auto it = utf8_range_separator.begin(); it != utf8_range_separator.end(); ++it) {
-        if (Unicode::code_point_has_property(*it, Unicode::Property::White_Space))
-            return {};
-    }
-
-    // 1. If the lower string ends with a character other than a digit, or if the upper string begins with a character other than a digit.
-    if (auto it = utf8_upper.begin(); it != utf8_upper.end()) {
-        if (!Unicode::code_point_has_general_category(*it, Unicode::GeneralCategory::Decimal_Number))
-            return range_pattern_with_spacing();
-    }
-
-    if (!Unicode::code_point_has_general_category(last_code_point(lower), Unicode::GeneralCategory::Decimal_Number))
-        return range_pattern_with_spacing();
-#endif
-
-    return {};
-}
-
 }

Userland/Libraries/LibLocale/NumberFormat.h

@@ -151,6 +151,7 @@ public:
     struct Partition {
         StringView type;
         String value;
+        StringView source;
     };
 
     using Value = Variant<double, String>;
@@ -159,6 +160,9 @@ public:
     virtual String format_to_decimal(Value const&) const = 0;
     virtual Vector<Partition> format_to_parts(Value const&) const = 0;
 
+    virtual String format_range(Value const&, Value const&) const = 0;
+    virtual Vector<Partition> format_range_to_parts(Value const&, Value const&) const = 0;
+
 protected:
     NumberFormat() = default;
 };
@@ -181,6 +185,4 @@ Optional<StringView> get_number_system_symbol(StringView locale, StringView syst
 Optional<ReadonlySpan<u32>> get_digits_for_number_system(StringView system);
 String replace_digits_for_number_system(StringView system, StringView number);
 
-Optional<String> augment_range_pattern(StringView range_separator, StringView lower, StringView upper);
-
 }