JVM Json Serialization Broken with Array<Array<Primitive> types

Describe the bug

Given the following code

@Serializable
    data class Matrix2(val data: Array<Array<Int>>) {
        override fun equals(other: Any?): Boolean {
            if (this === other) return true
            if (other == null || this::class != other::class) return false

            other as Matrix2

            if (!data.contentDeepEquals(other.data)) return false

            return true
        }

        override fun hashCode(): Int {
            return data.contentDeepHashCode()
        }
    }

    @Test
    fun test() {
        val m = Matrix2(
            arrayOf(
                arrayOf(1, 0, 0),
                arrayOf(0, 1, 0),
                arrayOf(0, 0, 1)
            )
        )
        val json = Json.encodeToString(m)
        val result: Matrix2 = Json.decodeFromString(json)

        assertEquals(m, result)
    }

The test should pass, but on the JVM it fails with the following error.

java.lang.ClassCastException: class [[Ljava.lang.Object; cannot be cast to class [[Ljava.lang.Integer; ([[Ljava.lang.Object; and [[Ljava.lang.Integer; are in module java.base of loader 'bootstrap')
	at serialization.JsonSerializationTest$Matrix2$$serializer.deserialize(JsonSerializationTest.kt:68)
	at serialization.JsonSerializationTest$Matrix2$$serializer.deserialize(JsonSerializationTest.kt:68)
	at kotlinx.serialization.json.internal.PolymorphicKt.decodeSerializableValuePolymorphic(Polymorphic.kt:63)
	at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableValue(StreamingJsonDecoder.kt:32)
	at kotlinx.serialization.json.Json.decodeFromString(Json.kt:85)
	at raytracer.serialization.JsonSerializationTest.test(JsonSerializationTest.kt:111)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)

The generic type of Array<Array<Int> can be changed to any other primitive and the same behavior occurs. On js targets and native targets the code works as expected.

Expected behavior

Expected behavior would be that the Matrix2 class would be able to be serialized and deserialized on all target platforms.

Environment kotlin = 1.4.32 kotlinx-serialization = 1.1.0 gradle = 7.0 jvm = 11.0.2 (Oracle Corporation 11.0.2+9)

[qwwdfsad]

Fixed in Kotlin 1.5.0+

[sandwwraith]

@judos That was a bug in the compiler plugin, that has the same versioning as the Kotlin compiler itself.