IllegalStateException: Invisible parameter type of kotlin.jvm.internal.DefaultConstructorMarker

I have a Kotlin class:

open class SomeClass(val cheese: String = "brie") {
    fun foo() = "bar"
}

… and a Spock test:

class SomeClassTest extends Specification {

    def "should be able to mock"() {
      given:
        def someMock = Mock(SomeClass)
        someMock.foo() >> "cheese"

      expect: "that we actually can mock it"
        someMock.cheese == "brie"
        someMock.foo() == "cheese"
    }
}

… using the following Gradle dependencies:

testCompile(
    "org.spockframework:spock-core:1.1-groovy-2.4",
    "net.bytebuddy:byte-buddy:1.7.5",
)

Running the test gives me:

java.lang.IllegalArgumentException: Could not create type

	at net.bytebuddy.TypeCache.findOrInsert(TypeCache.java:140)
	at net.bytebuddy.TypeCache$WithInlineExpunction.findOrInsert(TypeCache.java:346)
	at net.bytebuddy.TypeCache.findOrInsert(TypeCache.java:161)
	at net.bytebuddy.TypeCache$WithInlineExpunction.findOrInsert(TypeCache.java:355)
	at org.spockframework.mock.runtime.ProxyBasedMockFactory$ByteBuddyMockFactory.createMock(ProxyBasedMockFactory.java:108)
	at org.spockframework.mock.runtime.ProxyBasedMockFactory.create(ProxyBasedMockFactory.java:65)
	at org.spockframework.mock.runtime.JavaMockFactory.createInternal(JavaMockFactory.java:59)
	at org.spockframework.mock.runtime.JavaMockFactory.create(JavaMockFactory.java:40)
	at org.spockframework.mock.runtime.CompositeMockFactory.create(CompositeMockFactory.java:44)
	at org.spockframework.lang.SpecInternals.createMock(SpecInternals.java:51)
	at org.spockframework.lang.SpecInternals.createMockImpl(SpecInternals.java:296)
	at org.spockframework.lang.SpecInternals.createMockImpl(SpecInternals.java:286)
	at org.spockframework.lang.SpecInternals.MockImpl(SpecInternals.java:105)
	at no.finn.travel.shared.common.kotlin.OpenTest.should be able to mock #subject(OpenTest.groovy:11)
Caused by: java.lang.IllegalStateException: Invisible parameter type of kotlin.jvm.internal.DefaultConstructorMarker arg2 for public no.finn.travel.shared.common.kotlin.SomeClass$SpockMock$bAkOnnH5(java.lang.String,int,kotlin.jvm.internal.DefaultConstructorMarker)
	at net.bytebuddy.dynamic.scaffold.InstrumentedType$Default.validated(InstrumentedType.java:925)
	at net.bytebuddy.dynamic.scaffold.MethodRegistry$Default.prepare(MethodRegistry.java:465)
	at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:162)
	at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:155)
	at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase.make(DynamicType.java:2639)
	at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$Delegator.make(DynamicType.java:2741)
	at org.spockframework.mock.runtime.ProxyBasedMockFactory$ByteBuddyMockFactory$1.call(ProxyBasedMockFactory.java:113)
	at org.spockframework.mock.runtime.ProxyBasedMockFactory$ByteBuddyMockFactory$1.call(ProxyBasedMockFactory.java:110)
	at net.bytebuddy.TypeCache.findOrInsert(TypeCache.java:138)
	... 13 more

The test works without the byte-buddy dependency.

[raphw]

This seems like a bug in Kotlin. Its compiler creates a synthetic constructor: public synthetic <init>(Ljava/lang/String;ILkotlin/jvm/internal/DefaultConstructorMarker;

The DefaultConstructorMarker type is package-private and therefore not visible to SomeClass$SpockMock. According to the spec, this is not legal as you must not refer to classes that are not visible to a class but the JVM is sometimes more forgiving like in this case.

The javac compiler does a similar thing but creates an anonymous type in the same package of the class it creates. The Kotlin compiler should do the same thing or make the default marker type public (whilst it could still retain the class’s constructor public.)

[raphw]

Its on my agenda and I hope to find some time next week!