Fix resize in JsonPath

Author: larshagencognite

formats/json-tests/commonTest/src/kotlinx/serialization/JsonPathTest.kt

@@ -156,6 +156,27 @@ class JsonPathTest : JsonTestBase() {
         expectPath(expectedPath) { json.decodeFromString(Sealed.serializer(), malformed) }
     }
 
+    @Serializable
+    data class SimpleNested(val n: SimpleNested? = null, val t: DataObject? = null)
+
+    @Serializable
+    data object DataObject
+
+    @Test
+    fun testMalformedDataObjectInDeeplyNestedStructure() {
+        var outer = SimpleNested(t = DataObject)
+        repeat(20) {
+            outer = SimpleNested(n = outer)
+        }
+        val str = Json.encodeToString(SimpleNested.serializer(), outer)
+        // throw-away data
+        Json.decodeFromString(SimpleNested.serializer(), str)
+
+        val malformed = str.replace("{}", "42")
+        val expectedPath = "$" + ".n".repeat(20) + ".t\n"
+        expectPath(expectedPath) { Json.decodeFromString(SimpleNested.serializer(), malformed) }
+    }
+
     private inline fun expectPath(path: String, block: () -> Unit) {
         val message = runCatching { block() }
             .exceptionOrNull()!!.message!!

formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonPath.kt

@@ -134,7 +134,9 @@ internal class JsonPath {
     private fun resize() {
         val newSize = currentDepth * 2
         currentObjectPath = currentObjectPath.copyOf(newSize)
-        indicies = indicies.copyOf(newSize)
+        val newIndices = IntArray(newSize) { -1 }
+        indicies.copyInto(newIndices)
+        indicies = newIndices
     }
 
     override fun toString(): String = getPath()