Editorial: refactor offset string formatting

Simplify offset formatting by using FormatTimeString instead of bespoke
formatting logic. This commit completes the time-formatting refactor that
tc39#2629 started.

polyfill/lib/ecmascript.mjs

@@ -2209,22 +2209,15 @@ export function GetOffsetStringFor(timeZone, instant) {
 // In the spec, the code below only exists as part of GetOffsetStringFor.
 // But in the polyfill, we re-use it to provide clearer error messages.
 function formatOffsetStringNanoseconds(offsetNs) {
-  const offsetMinutes = MathTrunc(offsetNs / 6e10);
-  let offsetStringMinutes = FormatOffsetTimeZoneIdentifier(offsetMinutes);
-  const subMinuteNanoseconds = MathAbs(offsetNs) % 6e10;
-  if (!subMinuteNanoseconds) return offsetStringMinutes;
-
-  // For offsets between -1s and 0, exclusive, FormatOffsetTimeZoneIdentifier's
-  // return value of "+00:00" is incorrect if there are sub-minute units.
-  if (!offsetMinutes && offsetNs < 0) offsetStringMinutes = '-00:00';
-
-  const seconds = MathFloor(subMinuteNanoseconds / 1e9) % 60;
-  const secondString = ISODateTimePartString(seconds);
-  const nanoseconds = subMinuteNanoseconds % 1e9;
-  if (!nanoseconds) return `${offsetStringMinutes}:${secondString}`;
-
-  let fractionString = `${nanoseconds}`.padStart(9, '0').replace(/0+$/, '');
-  return `${offsetStringMinutes}:${secondString}.${fractionString}`;
+  const sign = offsetNs < 0 ? '-' : '+';
+  const absoluteNs = MathAbs(offsetNs);
+  const hour = MathFloor(absoluteNs / 3600e9);
+  const minute = MathFloor(absoluteNs / 60e9) % 60;
+  const second = MathFloor(absoluteNs / 1e9) % 60;
+  const subSecondNs = absoluteNs % 1e9;
+  const precision = second === 0 && subSecondNs === 0 ? 'minute' : 'auto';
+  const timeString = FormatTimeString(hour, minute, second, subSecondNs, precision);
+  return `${sign}${timeString}`;
 }
 
 export function GetPlainDateTimeFor(timeZone, instant, calendar) {
@@ -2742,11 +2735,10 @@ export function GetNamedTimeZoneOffsetNanoseconds(id, epochNanoseconds) {
 export function FormatOffsetTimeZoneIdentifier(offsetMinutes) {
   const sign = offsetMinutes < 0 ? '-' : '+';
   const absoluteMinutes = MathAbs(offsetMinutes);
-  const intHours = MathFloor(absoluteMinutes / 60);
-  const hh = ISODateTimePartString(intHours);
-  const intMinutes = absoluteMinutes % 60;
-  const mm = ISODateTimePartString(intMinutes);
-  return `${sign}${hh}:${mm}`;
+  const hour = MathFloor(absoluteMinutes / 60);
+  const minute = absoluteMinutes % 60;
+  const timeString = FormatTimeString(hour, minute, 0, 0, 'minute');
+  return `${sign}${timeString}`;
 }
 
 export function FormatDateTimeUTCOffsetRounded(offsetNanoseconds) {

spec/abstractops.html

@@ -719,26 +719,26 @@ <h1>
         _minute_: an integer,
         _second_: an integer,
         _subSecondNanoseconds_: an integer,
-        _precision_: an integer in the inclusive range 0 to 9, *"minute"*, or *"auto"*
+        _precision_: an integer in the inclusive range 0 to 9, *"minute"*, *"minute-legacy"*, or *"auto"*
       ): a String
     </h1>
     <dl class="header">
       <dt>description</dt>
       <dd>
         The output will be formatted like ±HH:MM if _precision_ is *"minute"*.
-        Otherwise, the output will be formatted like ±HH:MM:SS if _precision_ is zero, or if _subSecondNanoseconds_ is zero and _precision is *"auto"*.
+        The output will be formatted like ±HHMM if _precision_ is *"minute-legacy"*.
+        Otherwise, the output will be formatted like ±HH:MM:SS if _precision_ is zero, or if _subSecondNanoseconds_ is zero and _precision_ is *"auto"*.
         Otherwise, the output will be formatted like ±HH:MM:SS.fff where "fff" is a sequence of fractional seconds digits, truncated to _precision_ digits or (if _precision_ is *"auto"*) to the last non-zero digit.
       </dd>
     </dl>
     <emu-alg>
       1. Let _hh_ be ToZeroPaddedDecimalString(_hour_, 2).
       1. Let _mm_ be ToZeroPaddedDecimalString(_minute_, 2).
-      1. Let _result_ be the string-concatenation of _hh_, the code unit 0x003A (COLON), and _mm_.
-      1. If _precision_ is *"minute"*, return _result_.
+      1. If _precision_ is *"minute-legacy"*, return the string-concatenation of _hh_ and _mm_.
+      1. If _precision_ is *"minute"*, return the string-concatenation of _hh_, the code unit 0x003A (COLON), and _mm_.
       1. Let _ss_ be ToZeroPaddedDecimalString(_second_, 2).
       1. Let _subSecondsPart_ be FormatFractionalSeconds(_subSecondNanoseconds_, _precision_).
-      1. Set _result_ to the string-concatenation of _result_, the code unit 0x003A (COLON), _ss_, and _subSecondsPart_.
-      1. Return _result_.
+      1. Return the string-concatenation of _hh_, the code unit 0x003A (COLON), _mm_, the code unit 0x003A (COLON), _ss_, and _subSecondsPart_.
     </emu-alg>
   </emu-clause>
 

spec/timezone.html

@@ -488,13 +488,11 @@ <h1>
       <emu-alg>
         1. If _offsetMinutes_ &ge; 0, let _sign_ be the code unit 0x002B (PLUS SIGN); otherwise, let _sign_ be the code unit 0x002D (HYPHEN-MINUS).
         1. Let _absoluteMinutes_ be abs(_offsetMinutes_).
-        1. Let _intHours_ be floor(_absoluteMinutes_ / 60).
-        1. Let _hh_ be ToZeroPaddedDecimalString(_intHours_, 2).
-        1. Let _intMinutes_ be _absoluteMinutes_ modulo 60.
-        1. Let _mm_ be ToZeroPaddedDecimalString(_intMinutes_, 2).
-        1. If _style_ is ~legacy~, then
-          1. Return the string-concatenation of _sign_, _hh_, and _mm_.
-        1. Return the string-concatenation of _sign_, _hh_, the code unit 0x003A (COLON), and _mm_.
+        1. Let _hour_ be floor(_absoluteMinutes_ / 60).
+        1. Let _minute_ be _absoluteMinutes_ modulo 60.
+        1. If _style_ is ~legacy~, let _precision_ be *"minute-legacy"*; otherwise, let _precision_ be *"minute"*.
+        1. Let _timeString_ be FormatTimeString(_hour_, _minute_, 0, 0, _precision_).
+        1. Return the string-concatenation of _sign_ and _timeString_.
       </emu-alg>
     </emu-clause>
 
@@ -653,20 +651,15 @@ <h1>
       </dl>
       <emu-alg>
         1. Let _offsetNanoseconds_ be ? GetOffsetNanosecondsFor(_timeZone_, _instant_).
-        1. Let _offsetMinutes_ be truncate(_offsetNanoseconds_ / (6 × 10<sup>10</sup>)).
-        1. Let _offsetString_ be FormatOffsetTimeZoneIdentifier(_offsetMinutes_, ~separate~).
-        1. Let _subMinuteNanoseconds_ be abs(_offsetNanoseconds_) modulo (6 × 10<sup>10</sup>).
-        1. If _subMinuteNanoseconds_ = 0, then
-          1. Return _offsetString_.
-        1. If _offsetMinutes_ = 0 and _offsetNanoseconds_ &lt; 0, set _offsetString_ to *"-00:00"*.
-        1. Let _seconds_ be floor(_subMinuteNanoseconds_ / 10<sup>9</sup>) modulo 60.
-        1. Let _ss_ be ToZeroPaddedDecimalString(_seconds_, 2).
-        1. Let _nanoseconds_ be _subMinuteNanoseconds_ modulo 10<sup>9</sup>.
-        1. If _nanoseconds_ = 0, then
-          1. Return the string-concatenation of _offsetString_, the code unit 0x003A (COLON), and _ss_.
-        1. Let _fractionString_ be ToZeroPaddedDecimalString(_nanoseconds_, 9).
-        1. Set _fractionString_ to the longest prefix of _fractionString_ ending with a code unit other than 0x0030 (DIGIT ZERO).
-        1. Return the string-concatenation of _offsetString_, the code unit 0x003A (COLON), _ss_, the code unit 0x002E (FULL STOP), and _fractionString_.
+        1. If _offsetNanoseconds_ &ge; 0, let _sign_ be the code unit 0x002B (PLUS SIGN); otherwise, let _sign_ be the code unit 0x002D (HYPHEN-MINUS).
+        1. Let _absoluteNanoseconds_ be abs(_offsetNanoseconds_).
+        1. Let _hour_ be floor(_absoluteNanoseconds_ / (3600 × 10<sup>9</sup>)).
+        1. Let _minute_ be floor(_absoluteNanoseconds_ / (60 × 10<sup>9</sup>)) modulo 60.
+        1. Let _second_ be floor(_absoluteNanoseconds_ / 10<sup>9</sup>) modulo 60.
+        1. Let _subSecondNanoseconds_ be _absoluteNanoseconds_ modulo 10<sup>9</sup>.
+        1. If _second_ = 0 and _subSecondNanoseconds_ = 0, let _precision_ be *"minute"*; otherwise, let _precision_ be *"auto"*.
+        1. Let _timeString_ be FormatTimeString(_hour_, _minute_, _second_, _subSecondNanoseconds_, _precision_).
+        1. Return the string-concatenation of _sign_ and _timeString_.
       </emu-alg>
     </emu-clause>