LibJS: Selectively display DateTimeFormat day periods as noon

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

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Find.h>
 #include <AK/IterationDecision.h>
 #include <AK/NumericLimits.h>
 #include <LibJS/Runtime/AbstractOperations.h>
@@ -503,6 +504,30 @@ static Optional<StyleAndValue> find_calendar_field(StringView name, Unicode::Cal
     return {};
 }
 
+static Optional<StringView> resolve_day_period(StringView locale, StringView calendar, Unicode::CalendarPatternStyle style, Span<PatternPartition const> pattern_parts, LocalTime local_time)
+{
+    // Use the "noon" day period if the locale has it, but only if the time is either exactly 12:00.00 or would be displayed as such.
+    if (local_time.hour == 12) {
+        auto it = find_if(pattern_parts.begin(), pattern_parts.end(), [&](auto const& part) {
+            if (part.type == "minute"sv && local_time.minute != 0)
+                return true;
+            if (part.type == "second"sv && local_time.second != 0)
+                return true;
+            if (part.type == "fractionalSecondDigits"sv && local_time.millisecond != 0)
+                return true;
+            return false;
+        });
+
+        if (it == pattern_parts.end()) {
+            auto noon_symbol = Unicode::get_calendar_day_period_symbol(locale, calendar, style, Unicode::DayPeriod::Noon);
+            if (noon_symbol.has_value())
+                return *noon_symbol;
+        }
+    }
+
+    return Unicode::get_calendar_day_period_symbol_for_hour(locale, calendar, style, local_time.hour);
+}
+
 // 11.5.6 FormatDateTimePattern ( dateTimeFormat, patternParts, x, rangeFormatOptions ), https://tc39.es/ecma402/#sec-formatdatetimepattern
 ThrowCompletionOr<Vector<PatternPartition>> format_date_time_pattern(GlobalObject& global_object, DateTimeFormat& date_time_format, Vector<PatternPartition> pattern_parts, double time, Unicode::CalendarPattern const* range_format_options)
 {
@@ -606,7 +631,7 @@ ThrowCompletionOr<Vector<PatternPartition>> format_date_time_pattern(GlobalObjec
             auto style = date_time_format.day_period();
 
             // ii. Let fv be a String value representing the day period of tm in the form given by f; the String value depends upon the implementation and the effective locale of dateTimeFormat.
-            auto symbol = Unicode::get_calendar_day_period_symbol_for_hour(data_locale, date_time_format.calendar(), style, local_time.hour);
+            auto symbol = resolve_day_period(data_locale, date_time_format.calendar(), style, pattern_parts, local_time);
             if (symbol.has_value())
                 formatted_value = *symbol;
 

Userland/Libraries/LibJS/Tests/builtins/Intl/DateTimeFormat/DateTimeFormat.prototype.format.js

@@ -273,6 +273,48 @@ describe("dayPeriod", () => {
         expect(en.format(date1)).toBe("5 at night");
         expect(en.format(date2)).toBe("11 at night");
     });
+
+    test("noon", () => {
+        const date0 = Date.UTC(2017, 11, 12, 12, 0, 0, 0);
+        const date1 = Date.UTC(2017, 11, 12, 12, 1, 0, 0);
+        const date2 = Date.UTC(2017, 11, 12, 12, 0, 1, 0);
+        const date3 = Date.UTC(2017, 11, 12, 12, 0, 0, 500);
+
+        // prettier-ignore
+        const data = [
+            { minute: undefined, second: undefined, fractionalSecondDigits: undefined, en0: "12 noon", en1: "12 noon", en2: "12 noon", en3: "12 noon", ar0: "١٢ ظهرًا", ar1: "١٢ ظهرًا", ar2: "١٢ ظهرًا", ar3: "١٢ ظهرًا" },
+            { minute: "numeric", second: undefined, fractionalSecondDigits: undefined, en0: "12:00 noon", en1: "12:01 in the afternoon", en2: "12:00 noon", en3: "12:00 noon", ar0: "١٢:٠٠ ظهرًا", ar1: "١٢:٠١ ظهرًا", ar2: "١٢:٠٠ ظهرًا", ar3: "١٢:٠٠ ظهرًا" },
+            { minute: "numeric", second: "numeric", fractionalSecondDigits: undefined, en0: "12:00:00 noon", en1: "12:01:00 in the afternoon", en2: "12:00:01 in the afternoon", en3: "12:00:00 noon", ar0: "١٢:٠٠:٠٠ ظهرًا", ar1: "١٢:٠١:٠٠ ظهرًا", ar2: "١٢:٠٠:٠١ ظهرًا", ar3: "١٢:٠٠:٠٠ ظهرًا" },
+            { minute: "numeric", second: "numeric", fractionalSecondDigits: 1, en0: "12:00:00.0 noon", en1: "12:01:00.0 in the afternoon", en2: "12:00:01.0 in the afternoon", en3: "12:00:00.5 in the afternoon", ar0: "١٢:٠٠:٠٠٫٠ ظهرًا", ar1: "١٢:٠١:٠٠٫٠ ظهرًا", ar2: "١٢:٠٠:٠١٫٠ ظهرًا", ar3: "١٢:٠٠:٠٠٫٥ ظهرًا" },
+        ];
+
+        // The en locale includes the "noon" fixed day period, whereas the ar locale does not.
+        data.forEach(d => {
+            const en = new Intl.DateTimeFormat("en", {
+                dayPeriod: "short",
+                timeZone: "UTC",
+                minute: d.minute,
+                second: d.second,
+                fractionalSecondDigits: d.fractionalSecondDigits,
+            });
+            expect(en.format(date0)).toBe(d.en0);
+            expect(en.format(date1)).toBe(d.en1);
+            expect(en.format(date2)).toBe(d.en2);
+            expect(en.format(date3)).toBe(d.en3);
+
+            const ar = new Intl.DateTimeFormat("ar", {
+                dayPeriod: "short",
+                timeZone: "UTC",
+                minute: d.minute,
+                second: d.second,
+                fractionalSecondDigits: d.fractionalSecondDigits,
+            });
+            expect(ar.format(date0)).toBe(d.ar0);
+            expect(ar.format(date1)).toBe(d.ar1);
+            expect(ar.format(date2)).toBe(d.ar2);
+            expect(ar.format(date3)).toBe(d.ar3);
+        });
+    });
 });
 
 describe("hour", () => {