ICU4C: Allow trailing whitespace after a match

icu4c/source/i18n/messageformat2_parser.cpp

@@ -2098,18 +2098,10 @@ void Parser::parseSelectors(UErrorCode& status) {
 
     // Parse variants
     while (isWhitespace(source[index]) || isKeyStart(source[index])) {
-        if (isWhitespace(source[index])) {
-            int32_t whitespaceStart = index;
-            parseOptionalWhitespace(status);
-            // Restore the precondition.
-            // Error out if we reached the end of input. The message
-            // cannot end with trailing whitespace if there are variants.
-            if (!inBounds(source, index)) {
-                // Use index of first whitespace for error message
-                index = whitespaceStart;
-                ERROR(parseError, status, index);
-                return;
-            }
+        // Trailing whitespace is allowed
+        parseOptionalWhitespace(status);
+        if (!inBounds(source, index)) {
+            return;
         }
 
         // At least one key is required

testdata/message2/syntax-errors-diagnostics.json

@@ -136,11 +136,6 @@
         "char": 28,
         "comment": "Trailing characters that are not whitespace"
     },
-    {
-        "src": ".match {$foo :string} {$bar :string}  one * {{one}}  * * {{other}}   ",
-        "char": 66,
-        "comment": "Trailing whitespace at end of message should not be accepted either"
-    },
     {
         "src": "empty { }",
         "char": 8,

testdata/message2/valid-tests.json

@@ -138,6 +138,11 @@
       "comment": "Test that parser and serializer treat optionally-escaped characters consistently",
       "src" : "{{{1}|}}",
       "exp": "1|"
+    },
+    {
+      "comment": "Trailing whitespace after match is valid",
+      "src": ".match {1 :string} * {{}} ",
+      "exp": ""
     }
   ]
 }