Disallow formatRange() and formatRangeToParts() between different cal…

…endars

In Intl.DateTimeFormat.formatRange() and formatRangeToParts(), check if
the calendars of the two operands are different. If they are different,
then throw. The previous behaviour was to throw only if both calendars
were non-ISO.

This brings the behaviour in line with that of difference().

Closes: #587

polyfill/lib/intl.mjs

@@ -59,7 +59,7 @@ function resolvedOptions() {
 
 function adjustFormatterCalendar(formatter, calendar) {
   const options = formatter.resolvedOptions();
-  if (!calendar || calendar === options.calendar || calendar === 'gregory' || calendar === 'iso8601') return formatter;
+  if (!calendar || calendar === options.calendar || calendar === 'iso8601') return formatter;
   const locale = `${options.locale}-u-ca-${calendar}`;
   return new IntlDateTimeFormat(locale, options);
 }
@@ -68,8 +68,6 @@ function pickRangeCalendar(a, b) {
   if (!a) return b;
   if (!b) return a;
   if (a === b) return a;
-  if (a === 'iso8601' || a === 'gregory') return b;
-  if (b === 'iso8601' || b === 'gregory') return a;
   throw new RangeError(`cannot format range between two dates of ${a} and ${b} calendars`);
 }
 

polyfill/test/intl.mjs

@@ -334,6 +334,16 @@ describe('Intl', () => {
       });
       it('should throw a TypeError when called with dissimilar types', () =>
         throws(() => us.formatRange(Temporal.Absolute.from(t1), Temporal.DateTime.from(t2)), TypeError));
+      it('should throw a RangeError when called with different calendars', () => {
+        throws(
+          () => us.formatRange(Temporal.DateTime.from(t1), Temporal.DateTime.from(t2).withCalendar('japanese')),
+          RangeError
+        );
+        throws(
+          () => us.formatRange(Temporal.Date.from(t1), Temporal.Date.from(t2).withCalendar('japanese')),
+          RangeError
+        );
+      });
     });
     describe('formatRangeToParts', () => {
       it('should work for Absolute', () => {
@@ -579,6 +589,16 @@ describe('Intl', () => {
       });
       it('should throw a TypeError when called with dissimilar types', () =>
         throws(() => at.formatRangeToParts(Temporal.Absolute.from(t1), Temporal.DateTime.from(t2)), TypeError));
+      it('should throw a RangeError when called with different calendars', () => {
+        throws(
+          () => at.formatRangeToParts(Temporal.DateTime.from(t1), Temporal.DateTime.from(t2).withCalendar('japanese')),
+          RangeError
+        );
+        throws(
+          () => at.formatRangeToParts(Temporal.Date.from(t1), Temporal.Date.from(t2).withCalendar('japanese')),
+          RangeError
+        );
+      });
     });
   });
 });