Fix bug where PlainDateTime since/until would maintain date/time-diff…

… sign compatibility by backing-off from wrong end and erroneously falling across month boundaries
tc39 · May 14, 2024 · 20790d7 · 20790d7
1 parent c0be58d
commit 20790d7
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/polyfill/lib/ecmascript.mjs b/polyfill/lib/ecmascript.mjs
@@ -3879,8 +3879,10 @@ export function DifferenceISODateTime(
 
   const timeSign = timeDuration.sign();
   const dateSign = CompareISODate(y2, mon2, d2, y1, mon1, d1);
+
+  // back-off a day from date2 so that the signs of the date a time diff match
   if (dateSign === -timeSign) {
-    ({ year: y1, month: mon1, day: d1 } = BalanceISODate(y1, mon1, d1 - timeSign));
+    ({ year: y2, month: mon2, day: d2 } = BalanceISODate(y2, mon2, d2 + timeSign));
     timeDuration = timeDuration.add24HourDays(-timeSign);
   }