From 22ce1cdd1ceeb4d4a956de1a881f0d3103907e44 Mon Sep 17 00:00:00 2001
From: Tim Chevalier <tjc@igalia.com>
Date: Wed, 7 Aug 2024 13:04:50 -0700
Subject: [PATCH] ICU4J: Fix bug with '||' in a reserved statement being
 misparsed

---
 .../core/src/main/java/com/ibm/icu/message2/MFParser.java     | 4 +++-
 testdata/message2/reserved-syntax-2.json                      | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/icu4j/main/core/src/main/java/com/ibm/icu/message2/MFParser.java b/icu4j/main/core/src/main/java/com/ibm/icu/message2/MFParser.java
index 65e7d3e3e9b9..94470b9271ce 100644
--- a/icu4j/main/core/src/main/java/com/ibm/icu/message2/MFParser.java
+++ b/icu4j/main/core/src/main/java/com/ibm/icu/message2/MFParser.java
@@ -369,8 +369,10 @@ private String getReservedBody() throws MFParseException {
         result.append(firstPart);
         while (true) {
             int spaceCount = skipWhitespaces();
+            int beforeNextPart = input.getPosition();
             String nextPart = getReservedBodyPart();
-            if (nextPart.length() == 0) {
+            // If we didn't parse anything, restore the whitespace
+            if (input.getPosition() <= beforeNextPart) {
                 input.backup(spaceCount);
                 break;
             }
diff --git a/testdata/message2/reserved-syntax-2.json b/testdata/message2/reserved-syntax-2.json
index 23e115f8206b..e8ef9a782a69 100644
--- a/testdata/message2/reserved-syntax-2.json
+++ b/testdata/message2/reserved-syntax-2.json
@@ -8,7 +8,8 @@
       { "src" : "\\\\{   ?   󗟋   𫓜|@}   |}", "ignoreCpp": "This would be an error in ICU4C" },
       { "src" : "\\\\{   ?   󗟋   𫓜|@}   |   \\}   @𠟅򑚎𥪙𽧫=||   @򒘒򳷦㥞򉊷=$򸚶񽱆񅗽񤕞   @𰺱:񎫛񢶛򶈎񄮒}", "ignoreCpp": "This would be an error in ICU4C" },
       { "src" : "{  $iFN  ^  @USh  =$u  @l}", "ignoreCpp": "This would be an error in ICU4C" },
-      { "src" : ".local $dS ={ $p4 ^ |.| \\\\ @g:FV = $kd}{{@}}", "ignoreCpp": "This would be an error in ICU4C" }
+      { "src" : ".local $dS ={ $p4 ^ |.| \\\\ @g:FV = $kd}{{@}}", "ignoreCpp": "This would be an error in ICU4C" },
+      { "src" : ".D. \\\\ ||{1}{{}} ", "ignoreCpp": "This would be an error in ICU4C" }
   ]
 }