Avoid formatting irrelevant parts of dateStyle/timeStyle for Temporal…

… types

timeStyle: 'long' and timeStyle: 'full' include the time zone name for
legacy Date formatting. However, PlainTime and PlainDateTime don't include
a time zone in their data model, so they shouldn't format a time zone name
when using timeStyle. Similarly, PlainYearMonth and PlainMonthDay
shouldn't format a day or year respectively when using dateStyle. This was
already the consensus but somewhere along the line the spec text got out
of sync, probably in a rebase on latest ECMA-402.

In the polyfill, we already handled dateStyle for PlainYearMonth and
PlainMonthDay. Try to hack around this the same way for timeStyle.

Closes: #2795

polyfill/lib/intl.mjs

@@ -329,6 +329,11 @@ function timeAmend(originalOptions) {
     timeZoneName: false,
     dateStyle: false
   });
+  if (options.timeStyle === 'long' || options.timeStyle === 'full') {
+    // Try to fake what timeStyle should do if not printing the time zone name
+    delete options.timeStyle;
+    ObjectAssign(options, { hour: 'numeric', minute: '2-digit', second: '2-digit' });
+  }
   if (!hasTimeOptions(options)) {
     if (hasAnyDateTimeOptions(originalOptions)) {
       throw new TypeError(`cannot format Temporal.PlainTime with options [${ObjectKeys(originalOptions)}]`);
@@ -431,6 +436,11 @@ function dateAmend(originalOptions) {
 
 function datetimeAmend(originalOptions) {
   const options = amend(originalOptions, { timeZoneName: false });
+  if (options.timeStyle === 'long' || options.timeStyle === 'full') {
+    // Try to fake what timeStyle should do if not printing the time zone name
+    delete options.timeStyle;
+    ObjectAssign(options, { hour: 'numeric', minute: '2-digit', second: '2-digit' });
+  }
   if (!hasTimeOptions(options) && !hasDateOptions(options)) {
     if (hasAnyDateTimeOptions(originalOptions)) {
       throw new TypeError(`cannot format PlainDateTime with options [${ObjectKeys(originalOptions)}]`);

spec/intl.html

@@ -701,17 +701,17 @@ <h1>
           1. Let _bestFormat_ be DateTimeStyleFormat(_dateStyle_, _timeStyle_, _styles_).
           1. <ins>If _dateStyle_ is not *undefined*, then</ins>
             1. <ins>Set _dateTimeFormat_.[[TemporalPlainDateFormat]] to _bestFormat_.</ins>
-            1. <ins>Set _dateTimeFormat_.[[TemporalPlainYearMonthFormat]] to _bestFormat_.</ins>
-            1. <ins>Set _dateTimeFormat_.[[TemporalPlainMonthDayFormat]] to _bestFormat_.</ins>
+            1. <ins>Set _dateTimeFormat_.[[TemporalPlainYearMonthFormat]] to GetDateTimeFormat(_styles_, _formatMatcher_, _bestFormat_, ~year-month~, ~year-month~, ~relevant~).</ins>
+            1. <ins>Set _dateTimeFormat_.[[TemporalPlainMonthDayFormat]] to GetDateTimeFormat(_styles_, _formatMatcher_, _bestFormat_, ~month-day~, ~month-day~, ~relevant~).</ins>
           1. <ins>Else,</ins>
             1. <ins>Set _dateTimeFormat_.[[TemporalPlainDateFormat]] to *null*.</ins>
             1. <ins>Set _dateTimeFormat_.[[TemporalPlainYearMonthFormat]] to *null*.</ins>
             1. <ins>Set _dateTimeFormat_.[[TemporalPlainMonthDayFormat]] to *null*.</ins>
           1. <ins>If _timeStyle_ is not *undefined*, then</ins>
-            1. <ins>Set _dateTimeFormat_.[[TemporalPlainTimeFormat]] to _bestFormat_.</ins>
+            1. <ins>Set _dateTimeFormat_.[[TemporalPlainTimeFormat]] to GetDateTimeFormat(_styles_, _formatMatcher_, _bestFormat_, ~time~, ~time~, ~relevant~).</ins>
           1. <ins>Else,</ins>
             1. <ins>Set _dateTimeFormat_.[[TemporalPlainTimeFormat]] to *null*.</ins>
-          1. <ins>Set _dateTimeFormat_.[[TemporalPlainDateTimeFormat]] to _bestFormat_.</ins>
+          1. <ins>Set _dateTimeFormat_.[[TemporalPlainDateTimeFormat]] to GetDateTimeFormat(_styles_, _formatMatcher_, _bestFormat_, ~any~, ~all~, ~relevant~).</ins>
           1. <ins>Set _dateTimeFormat_.[[TemporalInstantFormat]] to _bestFormat_.</ins>
         1. Else,
           1. <del>Let _needDefaults_ be *true*.</del>