From ff8880537075fa5511bffbdea2d1a94a5f64f180 Mon Sep 17 00:00:00 2001
From: Joey Connor <stephen.m.connor@accenture.com>
Date: Thu, 18 Jun 2026 15:45:42 +0100
Subject: [PATCH] fix(cy): set abbreviated am/pm to yb/yh instead of inheriting
 from root
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The format/abbreviated and stand-alone/abbreviated am and pm entries for
Welsh (cy) were ↑↑↑, causing ICU to inherit AM/PM from the root locale.

Under ICU 77 (CLDR 47) this was masked by a lateral fallback that
resolved ↑↑↑ at the abbreviated width to the locale's own wide entries
(yb/yh). ICU 78 (CLDR 48) now resolves ↑↑↑ correctly against the
parent locale, surfacing the gap.

Fix: replace ↑↑↑ with explicit Welsh values yb (y bore, AM) and yh
(yr hwyr, PM) in both format/abbreviated and stand-alone/abbreviated
contexts, consistent with the existing wide entries.

Also adds four datetime test cases (hm/hms × AM/PM) for locale cy to
prevent silent regression.

Identified via: commit f81989f8b (CLDR-18850 v48 vxml merge to main)
---
 common/main/cy.xml                     |  8 +--
 common/testData/datetime/datetime.json | 80 ++++++++++++++++++++++++++
 2 files changed, 84 insertions(+), 4 deletions(-)

diff --git a/common/main/cy.xml b/common/main/cy.xml
index 535c6962956..7070d126a57 100644
--- a/common/main/cy.xml
+++ b/common/main/cy.xml
@@ -1702,9 +1702,9 @@ Warnings: All cp values have U+FE0F characters removed. See /annotationsDerived/
 					<dayPeriodContext type="format">
 						<dayPeriodWidth type="abbreviated">
 							<dayPeriod type="midnight">canol nos</dayPeriod>
-							<dayPeriod type="am">↑↑↑</dayPeriod>
+							<dayPeriod type="am">yb</dayPeriod>
 							<dayPeriod type="noon">canol dydd</dayPeriod>
-							<dayPeriod type="pm">↑↑↑</dayPeriod>
+							<dayPeriod type="pm">yh</dayPeriod>
 							<dayPeriod type="morning1">y bore</dayPeriod>
 							<dayPeriod type="afternoon1">y prynhawn</dayPeriod>
 							<dayPeriod type="evening1">yr hwyr</dayPeriod>
@@ -1731,9 +1731,9 @@ Warnings: All cp values have U+FE0F characters removed. See /annotationsDerived/
 					<dayPeriodContext type="stand-alone">
 						<dayPeriodWidth type="abbreviated">
 							<dayPeriod type="midnight">↑↑↑</dayPeriod>
-							<dayPeriod type="am">↑↑↑</dayPeriod>
+							<dayPeriod type="am">yb</dayPeriod>
 							<dayPeriod type="noon">↑↑↑</dayPeriod>
-							<dayPeriod type="pm">↑↑↑</dayPeriod>
+							<dayPeriod type="pm">yh</dayPeriod>
 							<dayPeriod type="morning1">bore</dayPeriod>
 							<dayPeriod type="afternoon1">prynhawn</dayPeriod>
 							<dayPeriod type="evening1">↑↑↑</dayPeriod>
diff --git a/common/testData/datetime/datetime.json b/common/testData/datetime/datetime.json
index 06dbdc7c52b..f883e6d38f1 100644
--- a/common/testData/datetime/datetime.json
+++ b/common/testData/datetime/datetime.json
@@ -2886,5 +2886,85 @@
     "locale": "ja-JP",
     "input": "2014-07-15T12:00Z[Etc/GMT]",
     "expected": "12:00:00"
+  },
+  {
+    "semanticSkeleton": "T",
+    "semanticSkeletonLength": "short",
+    "classicalSkeleton": "hm",
+    "hourCycle": "H12",
+    "calendar": "gregorian",
+    "locale": "cy",
+    "input": "2024-07-01T09:30:00Z[Etc/GMT]",
+    "expected": "9:30 yb"
+  },
+  {
+    "semanticSkeleton": "T",
+    "semanticSkeletonLength": "short",
+    "classicalSkeleton": "hm",
+    "hourCycle": "H12",
+    "calendar": "gregorian",
+    "locale": "cy",
+    "input": "2024-07-01T14:30:00Z[Etc/GMT]",
+    "expected": "2:30 yh"
+  },
+  {
+    "semanticSkeleton": "T",
+    "semanticSkeletonLength": "short",
+    "classicalSkeleton": "hms",
+    "hourCycle": "H12",
+    "calendar": "gregorian",
+    "locale": "cy",
+    "input": "2024-07-01T09:30:00Z[Etc/GMT]",
+    "expected": "9:30:00 yb"
+  },
+  {
+    "semanticSkeleton": "T",
+    "semanticSkeletonLength": "short",
+    "classicalSkeleton": "hms",
+    "hourCycle": "H12",
+    "calendar": "gregorian",
+    "locale": "cy",
+    "input": "2024-07-01T14:30:00Z[Etc/GMT]",
+    "expected": "2:30:00 yh"
+  },
+  {
+    "semanticSkeleton": "T",
+    "semanticSkeletonLength": "short",
+    "classicalSkeleton": "hm",
+    "hourCycle": "H12",
+    "calendar": "gregorian",
+    "locale": "cy",
+    "input": "2024-07-01T09:30:00Z[Etc/GMT]",
+    "expected": "9:30 yb"
+  },
+  {
+    "semanticSkeleton": "T",
+    "semanticSkeletonLength": "short",
+    "classicalSkeleton": "hm",
+    "hourCycle": "H12",
+    "calendar": "gregorian",
+    "locale": "cy",
+    "input": "2024-07-01T14:30:00Z[Etc/GMT]",
+    "expected": "2:30 yh"
+  },
+  {
+    "semanticSkeleton": "T",
+    "semanticSkeletonLength": "short",
+    "classicalSkeleton": "hms",
+    "hourCycle": "H12",
+    "calendar": "gregorian",
+    "locale": "cy",
+    "input": "2024-07-01T09:30:00Z[Etc/GMT]",
+    "expected": "9:30:00 yb"
+  },
+  {
+    "semanticSkeleton": "T",
+    "semanticSkeletonLength": "short",
+    "classicalSkeleton": "hms",
+    "hourCycle": "H12",
+    "calendar": "gregorian",
+    "locale": "cy",
+    "input": "2024-07-01T14:30:00Z[Etc/GMT]",
+    "expected": "2:30:00 yh"
   }
 ]