feat(js/ts/python): Add missing standard DateTime format specifiers for JS/TS and Python

src/fable-library-py/fable_library/date.py

@@ -167,6 +167,48 @@ def to_long_time_string(date: datetime) -> str:
     return datetime.strftime(date, "%H:%M:%S")
 
 
+def _to_plain_utc(date: datetime) -> datetime:
+    # Strip any datetime subclass (e.g. DateTimeOffset) so astimezone's internal
+    # reconstruction doesn't hit an incompatible __new__ signature.
+    plain = datetime(
+        date.year, date.month, date.day, date.hour, date.minute, date.second, date.microsecond, tzinfo=date.tzinfo
+    )
+    return plain.astimezone(UTC)
+
+
+def to_rfc1123_string(date: datetime) -> str:
+    """RFC 1123: "Thu, 01 Jan 2009 00:00:00 GMT" — always UTC"""
+    utc_date = _to_plain_utc(date)
+    return (
+        short_days[day_of_week(utc_date)]
+        + ", "
+        + utc_date.strftime("%d ")
+        + short_months[utc_date.month - 1]
+        + utc_date.strftime(" %Y %H:%M:%S GMT")
+    )
+
+
+def to_sortable_string(date: datetime) -> str:
+    """Sortable ISO 8601, no timezone: "2009-06-15T13:45:30" """
+    return date.strftime("%Y-%m-%dT%H:%M:%S")
+
+
+def to_universal_sortable_string(date: datetime) -> str:
+    """Universal sortable: "2009-06-15 13:45:30Z" — always UTC"""
+    utc_date = _to_plain_utc(date)
+    return utc_date.strftime("%Y-%m-%d %H:%M:%SZ")
+
+
+def to_month_day_string(date: datetime) -> str:
+    """Month/day (InvariantCulture "MMMM dd"): "June 15" """
+    return long_months[date.month - 1] + " " + f"{date.day:02d}"
+
+
+def to_year_month_string(date: datetime) -> str:
+    """Year/month (InvariantCulture "yyyy MMMM"): "2009 June" """
+    return str(date.year) + " " + long_months[date.month - 1]
+
+
 def parse_repeat_token(format: str, pos: int, pattern_char: str) -> int:
     token_length = 0
     internal_pos = pos
@@ -426,6 +468,35 @@ def date_to_string_with_offset(date: datetime, format: str | None = None) -> str
                 return date.strftime("%Y-%m-%dT%H:%M:%S.%f%z")
         case "O" | "o":
             return date.strftime("%Y-%m-%dT%H:%M:%S.%fZ")
+        case "D":
+            return to_long_date_string(date)
+        case "d":
+            return to_short_date_string(date)
+        case "F":
+            return to_long_date_string(date) + " " + to_long_time_string(date)
+        case "f":
+            return to_long_date_string(date) + " " + to_short_time_string(date)
+        case "G":
+            return to_short_date_string(date) + " " + to_long_time_string(date)
+        case "g":
+            return to_short_date_string(date) + " " + to_short_time_string(date)
+        case "M" | "m":
+            return to_month_day_string(date)
+        case "R" | "r":
+            return to_rfc1123_string(date)
+        case "s":
+            return to_sortable_string(date)
+        case "T":
+            return to_long_time_string(date)
+        case "t":
+            return to_short_time_string(date)
+        case "u":
+            return to_universal_sortable_string(date)
+        case "U":
+            utc_date = _to_plain_utc(date)
+            return to_long_date_string(utc_date) + " " + to_long_time_string(utc_date)
+        case "Y" | "y":
+            return to_year_month_string(date)
         case _ if len(format) == 1:
             raise Exception("Unrecognized Date print format")
         case _:
@@ -435,24 +506,44 @@ def date_to_string_with_offset(date: datetime, format: str | None = None) -> str
 def date_to_string_with_kind(date: datetime, format: str | None = None) -> str:
     utc = date.tzinfo == UTC
 
-    if not format:
-        return date.isoformat() if utc else str(date)
-    elif len(format) == 1:
-        if format == "d":
+    match format:
+        case None | "":
+            return date.isoformat() if utc else str(date)
+        case "d":
             return to_short_date_string(date)
-        elif format == "D":
+        case "D":
             return to_long_date_string(date)
-        elif format == "T":
+        case "F":
+            return to_long_date_string(date) + " " + to_long_time_string(date)
+        case "f":
+            return to_long_date_string(date) + " " + to_short_time_string(date)
+        case "G":
+            return to_short_date_string(date) + " " + to_long_time_string(date)
+        case "g":
+            return to_short_date_string(date) + " " + to_short_time_string(date)
+        case "M" | "m":
+            return to_month_day_string(date)
+        case "O" | "o":
+            return date.astimezone().isoformat(timespec="milliseconds")
+        case "R" | "r":
+            return to_rfc1123_string(date)
+        case "s":
+            return to_sortable_string(date)
+        case "T":
             return to_long_time_string(date)
-        elif format == "t":
+        case "t":
             return to_short_time_string(date)
-        elif format == "O" or format == "o":
-            return date.astimezone().isoformat(timespec="milliseconds")
-        else:
+        case "u":
+            return to_universal_sortable_string(date)
+        case "U":
+            utc_date = _to_plain_utc(date)
+            return to_long_date_string(utc_date) + " " + to_long_time_string(utc_date)
+        case "Y" | "y":
+            return to_year_month_string(date)
+        case _ if len(format) == 1:
             raise Exception("Unrecognized Date print format")
-
-    else:
-        return date_to_string_with_custom_format(date, format, utc)
+        case _:
+            return date_to_string_with_custom_format(date, format, utc)
 
 
 def to_string(date: datetime, format: str | None = None, provider: Any | None = None) -> str:

src/fable-library-ts/Date.ts

@@ -410,9 +410,28 @@ function dateToStringWithOffset(date: IDateTimeOffset, format?: string) {
     switch (format) {
       case "D": return dateToString_D(d);
       case "d": return dateToString_d(d);
+      case "F": return dateToString_D(d) + " " + dateToString_T(d);
+      case "f": return dateToString_D(d) + " " + dateToString_t(d);
+      case "G": return dateToString_d(d) + " " + dateToString_T(d);
+      case "g": return dateToString_d(d) + " " + dateToString_t(d);
+      case "M": case "m": return dateToString_M(d);
+      case "O": case "o": return dateToISOStringWithOffset(d, (date.offset ?? 0));
+      case "R": case "r": {
+        const utcDate = DateTime(date.getTime(), DateTimeKind.Utc);
+        return dateToString_R(utcDate);
+      }
+      case "s": return dateToString_s(d);
       case "T": return dateToString_T(toUniversalTime(d));
       case "t": return dateToString_t(toUniversalTime(d));
-      case "O": case "o": return dateToISOStringWithOffset(d, (date.offset ?? 0));
+      case "u": {
+        const utcDate = DateTime(date.getTime(), DateTimeKind.Utc);
+        return dateToString_u(utcDate);
+      }
+      case "U": {
+        const utcDate = DateTime(date.getTime(), DateTimeKind.Utc);
+        return dateToString_D(utcDate) + " " + dateToString_T(utcDate);
+      }
+      case "Y": case "y": return dateToString_Y(d);
       default: throw new Exception("Unrecognized Date print format");
     }
   } else {
@@ -444,6 +463,49 @@ function dateToString_t(date: IDateTime) {
     + ":" + padWithZeros(minute(date), 2);
 }
 
+// RFC 1123: "Thu, 01 Jan 2009 00:00:00 GMT" — always UTC
+function dateToString_R(date: IDateTime) {
+  const utcDate = toUniversalTime(date);
+  return shortDays[dayOfWeek(utcDate)] + ", "
+    + padWithZeros(day(utcDate), 2) + " "
+    + shortMonths[month(utcDate) - 1] + " "
+    + year(utcDate) + " "
+    + padWithZeros(hour(utcDate), 2) + ":"
+    + padWithZeros(minute(utcDate), 2) + ":"
+    + padWithZeros(second(utcDate), 2) + " GMT";
+}
+
+// Sortable ISO 8601, no timezone: "2009-06-15T13:45:30"
+function dateToString_s(date: IDateTime) {
+  return padWithZeros(year(date), 4) + "-"
+    + padWithZeros(month(date), 2) + "-"
+    + padWithZeros(day(date), 2) + "T"
+    + padWithZeros(hour(date), 2) + ":"
+    + padWithZeros(minute(date), 2) + ":"
+    + padWithZeros(second(date), 2);
+}
+
+// Universal sortable: "2009-06-15 13:45:30Z" — always UTC
+function dateToString_u(date: IDateTime) {
+  const utcDate = toUniversalTime(date);
+  return padWithZeros(year(utcDate), 4) + "-"
+    + padWithZeros(month(utcDate), 2) + "-"
+    + padWithZeros(day(utcDate), 2) + " "
+    + padWithZeros(hour(utcDate), 2) + ":"
+    + padWithZeros(minute(utcDate), 2) + ":"
+    + padWithZeros(second(utcDate), 2) + "Z";
+}
+
+// Month/day (InvariantCulture "MMMM dd"): "June 15"
+function dateToString_M(date: IDateTime) {
+  return longMonths[month(date) - 1] + " " + padWithZeros(day(date), 2);
+}
+
+// Year/month (InvariantCulture "yyyy MMMM"): "2009 June"
+function dateToString_Y(date: IDateTime) {
+  return year(date) + " " + longMonths[month(date) - 1];
+}
+
 function dateToStringWithKind(date: IDateTime, format?: string) {
   const utc = date.kind === DateTimeKind.Utc;
   if (typeof format !== "string") {
@@ -452,10 +514,19 @@ function dateToStringWithKind(date: IDateTime, format?: string) {
     switch (format) {
       case "D": return dateToString_D(date);
       case "d": return dateToString_d(date);
+      case "F": return dateToString_D(date) + " " + dateToString_T(date);
+      case "f": return dateToString_D(date) + " " + dateToString_t(date);
+      case "G": return dateToString_d(date) + " " + dateToString_T(date);
+      case "g": return dateToString_d(date) + " " + dateToString_t(date);
+      case "M": case "m": return dateToString_M(date);
+      case "O": case "o": return dateToISOString(date, utc);
+      case "R": case "r": return dateToString_R(date);
+      case "s": return dateToString_s(date);
       case "T": return dateToString_T(date);
       case "t": return dateToString_t(date);
-      case "O": case "o":
-        return dateToISOString(date, utc);
+      case "u": return dateToString_u(date);
+      case "U": return dateToString_D(toUniversalTime(date)) + " " + dateToString_T(toUniversalTime(date));
+      case "Y": case "y": return dateToString_Y(date);
       default:
         throw new Exception("Unrecognized Date print format");
     }

tests/Js/Main/DateTimeOffsetTests.fs

@@ -97,6 +97,21 @@ let tests =
         |> format
         |> equal "05:07"
 
+    testCase "DateTimeOffset.ToString('R') works" <| fun _ ->
+        // R always formats in UTC
+        DateTimeOffset(2014, 9, 1, 16, 37, 2, TimeSpan.FromHours 2).ToString("R", CultureInfo.InvariantCulture)
+        |> equal "Mon, 01 Sep 2014 14:37:02 GMT"
+
+    testCase "DateTimeOffset.ToString('u') works" <| fun _ ->
+        // u always formats in UTC
+        DateTimeOffset(2014, 9, 1, 16, 37, 2, TimeSpan.FromHours 2).ToString("u", CultureInfo.InvariantCulture)
+        |> equal "2014-09-01 14:37:02Z"
+
+    testCase "DateTimeOffset.ToString('s') works" <| fun _ ->
+        // s uses the offset-local time with no timezone designator
+        DateTimeOffset(2014, 9, 1, 16, 37, 2, TimeSpan.Zero).ToString("s", CultureInfo.InvariantCulture)
+        |> equal "2014-09-01T16:37:02"
+
     testCase "DateTimeOffset from Year 1 to 99 works" <| fun () ->
         let date = DateTimeOffset(1, 1, 2, 0, 0, 0, TimeSpan.Zero)
         date.Year |> equal 1

tests/Js/Main/DateTimeTests.fs

@@ -503,6 +503,60 @@ let tests =
     //     DateTime(2014, 9, 11, 16, 37, 2, DateTimeKind.Local).ToString("O")
     //     |> equal "2014-09-11T16:37:02.000+02:00" // Here the time zone is Europe/Paris (GMT+2)
 
+    testCase "DateTime.ToString('R') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("R", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "Mon, 01 Sep 2014 16:37:02 GMT"
+
+    testCase "DateTime.ToString('s') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("s", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "2014-09-01T16:37:02"
+
+    testCase "DateTime.ToString('u') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("u", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "2014-09-01 16:37:02Z"
+
+    testCase "DateTime.ToString('F') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("F", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "Monday, 01 September 2014 16:37:02"
+
+    testCase "DateTime.ToString('f') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("f", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "Monday, 01 September 2014 16:37"
+
+    testCase "DateTime.ToString('G') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("G", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "09/01/2014 16:37:02"
+
+    testCase "DateTime.ToString('g') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("g", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "09/01/2014 16:37"
+
+    testCase "DateTime.ToString('M') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("M", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "September 01"
+
+    testCase "DateTime.ToString('Y') works" <| fun _ ->
+        let format (d: DateTime) = d.ToString("Y", CultureInfo.InvariantCulture)
+        DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc)
+        |> format
+        |> equal "2014 September"
+
     testCase "DateTime from Year 1 to 99 works" <| fun () ->
         let date = DateTime(1, 1, 2)
         date.Year |> equal 1

tests/Python/TestDateTime.fs

@@ -556,6 +556,51 @@ let ``test DateTime.ToString with Round-trip format works for Utc`` () =
     str.Replace("0000000Z", "000000Z")
     |> equal "2014-09-11T16:37:02.000000Z"
 
+[<Fact>]
+let ``test DateTime.ToString("R") works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("R", CultureInfo.InvariantCulture)
+    |> equal "Mon, 01 Sep 2014 16:37:02 GMT"
+
+[<Fact>]
+let ``test DateTime.ToString("s") works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("s", CultureInfo.InvariantCulture)
+    |> equal "2014-09-01T16:37:02"
+
+[<Fact>]
+let ``test DateTime.ToString("u") works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("u", CultureInfo.InvariantCulture)
+    |> equal "2014-09-01 16:37:02Z"
+
+[<Fact>]
+let ``test DateTime.ToString full date long time format works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("F", CultureInfo.InvariantCulture)
+    |> equal "Monday, 01 September 2014 16:37:02"
+
+[<Fact>]
+let ``test DateTime.ToString full date short time format works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("f", CultureInfo.InvariantCulture)
+    |> equal "Monday, 01 September 2014 16:37"
+
+[<Fact>]
+let ``test DateTime.ToString general long time format works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("G", CultureInfo.InvariantCulture)
+    |> equal "09/01/2014 16:37:02"
+
+[<Fact>]
+let ``test DateTime.ToString general short time format works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("g", CultureInfo.InvariantCulture)
+    |> equal "09/01/2014 16:37"
+
+[<Fact>]
+let ``test DateTime.ToString("M") works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("M", CultureInfo.InvariantCulture)
+    |> equal "September 01"
+
+[<Fact>]
+let ``test DateTime.ToString("Y") works`` () =
+    DateTime(2014, 9, 1, 16, 37, 2, DateTimeKind.Utc).ToString("Y", CultureInfo.InvariantCulture)
+    |> equal "2014 September"
+
 [<Fact>]
 let ``test DateTime from Year 1 to 99 works`` () =
     let date = DateTime(1, 1, 2)