From 8f491b464719c6faa2e28240e377642b9aec13ac Mon Sep 17 00:00:00 2001
From: Philip Chimento <pchimento@igalia.com>
Date: Thu, 13 Feb 2025 16:03:22 -0800
Subject: [PATCH] Polyfill: Fix handling of hour12/hourCycle to conform to spec

The strategy of caching the output of DTF resolvedOptions() failed in the
case of hour12/hourCycle, because those options are silently dropped if
the chosen format does not include an hour component. Manually add them to
the cached resolvedOptions object if the user included them.

See: #3065
---
 polyfill/lib/intl.mjs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/polyfill/lib/intl.mjs b/polyfill/lib/intl.mjs
index cb56addf0..4a186851b 100644
--- a/polyfill/lib/intl.mjs
+++ b/polyfill/lib/intl.mjs
@@ -137,6 +137,11 @@ function createDateTimeFormat(dtf, locale, options) {
     for (const prop in clonedResolved) {
       if (!ES.HasOwnProperty(options, prop)) delete clonedResolved[prop];
     }
+    // hour12/hourCycle don't show up in resolvedOptions() unless the chosen
+    // format includes an hour component, so copy them explicitly in case they
+    // would otherwise be lost
+    clonedResolved.hour12 = options.hour12;
+    clonedResolved.hourCycle = options.hourCycle;
     SetSlot(dtf, OPTIONS, clonedResolved);
   } else {
     SetSlot(dtf, OPTIONS, options);