Fix PackedMap entry equality and hash codes (#27396)

core/src/main/java/hudson/util/PackedMap.java

@@ -92,22 +92,7 @@ public final class PackedMap<K, V> extends AbstractMap<K, V> {
                 public Entry<K, V> next() {
                     final K k = (K) kvpairs[index++];
                     final V v = (V) kvpairs[index++];
-                    return new Entry<>() {
-                        @Override
-                        public K getKey() {
-                            return k;
-                        }
-
-                        @Override
-                        public V getValue() {
-                            return v;
-                        }
-
-                        @Override
-                        public V setValue(V value) {
-                            throw new UnsupportedOperationException();
-                        }
-                    };
+                    return new SimpleImmutableEntry<>(k, v);
                 }
 
                 @Override

core/src/test/java/hudson/util/PackedMapTest.java

@@ -1,6 +1,7 @@
 package hudson.util;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -55,6 +56,19 @@ class PackedMapTest {
         xs.fromXML(xml);
     }
 
+    @Test
+    void entryEqualityAndHashCode() {
+        Map<String, String> source = Map.of("a", "b", "c", "d");
+        PackedMap<String, String> packed = PackedMap.of(source);
+
+        assertEquals(source.entrySet(), packed.entrySet());
+        assertEquals(packed.entrySet(), source.entrySet());
+        assertEquals(source.hashCode(), packed.hashCode());
+        assertEquals(packed.hashCode(), packed.hashCode());
+        assertThrows(UnsupportedOperationException.class,
+                () -> packed.entrySet().iterator().next().setValue("changed"));
+    }
+
     @Test
     void values() {
         Map<String, String> o = new TreeMap<>();