allow custom AnyValueGenerator

mockk/common/src/main/kotlin/io/mockk/impl/recording/CommonCallRecorder.kt

@@ -17,7 +17,7 @@ class CommonCallRecorder(
     val instantiator: AbstractInstantiator,
     val signatureValueGenerator: SignatureValueGenerator,
     val mockFactory: MockFactory,
-    val anyValueGenerator: AnyValueGenerator,
+    val anyValueGenerator: () -> AnyValueGenerator,
     val safeToString: SafeToString,
     val factories: CallRecorderFactories,
     val initialState: (CommonCallRecorder) -> CallRecordingState,

mockk/common/src/main/kotlin/io/mockk/impl/recording/states/RecordingState.kt

@@ -45,7 +45,7 @@ abstract class RecordingState(recorder: CommonCallRecorder) : CallRecordingState
     @Suppress("UNCHECKED_CAST")
     override fun <T : Any> matcher(matcher: Matcher<*>, cls: KClass<T>): T {
         val signatureValue = recorder.signatureValueGenerator.signatureValue(cls) {
-            recorder.anyValueGenerator.anyValue(cls, isNullable = false) {
+            recorder.anyValueGenerator().anyValue(cls, isNullable = false) {
                 recorder.instantiator.instantiate(cls)
             } as T
         }
@@ -67,7 +67,7 @@ abstract class RecordingState(recorder: CommonCallRecorder) : CallRecordingState
             if (invocation.method.isToString()) {
                 recorder.stubRepo[invocation.self]?.toStr() ?: ""
             } else {
-                recorder.anyValueGenerator.anyValue(retType, invocation.method.returnTypeNullable) {
+                recorder.anyValueGenerator().anyValue(retType, invocation.method.returnTypeNullable) {
                     isTemporaryMock = true
                     recorder.mockFactory.temporaryMock(retType)
                 }

mockk/common/src/main/kotlin/io/mockk/impl/stub/MockKStub.kt

@@ -83,7 +83,7 @@ open class MockKStub(
         return stdObjectFunctions(invocation.self, invocation.method, invocation.args) {
             if (shouldRelax(invocation)) {
                 if (invocation.method.returnsUnit) return Unit
-                return gatewayAccess.anyValueGenerator.anyValue(
+                return gatewayAccess.anyValueGenerator().anyValue(
                     invocation.method.returnType,
                     invocation.method.returnTypeNullable
                 ) {

mockk/common/src/main/kotlin/io/mockk/impl/stub/StubGatewayAccess.kt

@@ -7,7 +7,7 @@ import io.mockk.impl.log.SafeToString
 
 data class StubGatewayAccess(
     val callRecorder: () -> CallRecorder,
-    val anyValueGenerator: AnyValueGenerator,
+    val anyValueGenerator: () -> AnyValueGenerator,
     val stubRepository: StubRepository,
     val safeToString: SafeToString,
     val mockFactory: MockKGateway.MockFactory? = null

mockk/js/src/main/kotlin/io/mockk/impl/JsMockKGateway.kt

@@ -34,7 +34,7 @@ class JsMockKGateway : MockKGateway {
     override val mockFactory: MockFactory = JsMockFactory(
         stubRepo,
         instantiator,
-        StubGatewayAccess({ callRecorder }, anyValueGenerator, stubRepo, safeToString)
+        StubGatewayAccess({ callRecorder }, { anyValueGenerator }, stubRepo, safeToString)
     )
 
     override val clearer = CommonClearer(stubRepo, safeToString)
@@ -89,7 +89,7 @@ class JsMockKGateway : MockKGateway {
         instantiator,
         signatureValueGenerator,
         mockFactory,
-        anyValueGenerator,
+        { anyValueGenerator },
         safeToString,
         callRecorderFactories,
         { recorder -> callRecorderFactories.answeringState(recorder) },

mockk/jvm/src/main/kotlin/io/mockk/impl/JvmMockKGateway.kt

@@ -55,11 +55,16 @@ class JvmMockKGateway : MockKGateway {
         instanceFactoryRegistryIntrnl
     )
 
-    val anyValueGenerator = JvmAnyValueGenerator(instantiator.instantiate(Void::class))
+    val anyValueGeneratorProvider: () -> AnyValueGenerator = {
+        if (anyValueGenerator == null) {
+            anyValueGenerator = anyValueGeneratorFactory.invoke(instantiator.instantiate(Void::class))
+        }
+        anyValueGenerator!!
+    }
     val signatureValueGenerator = JvmSignatureValueGenerator(Random())
 
 
-    val gatewayAccess = StubGatewayAccess({ callRecorder }, anyValueGenerator, stubRepo, safeToString)
+    val gatewayAccess = StubGatewayAccess({ callRecorder }, anyValueGeneratorProvider, stubRepo, safeToString)
 
     override val mockFactory: AbstractMockFactory = JvmMockFactory(
         agentFactory.proxyMaker,
@@ -137,7 +142,7 @@ class JvmMockKGateway : MockKGateway {
             instantiator,
             signatureValueGenerator,
             mockFactory,
-            anyValueGenerator,
+            anyValueGeneratorProvider,
             safeToString,
             callRecorderFactories,
             { recorder -> callRecorderFactories.answeringState(recorder) },
@@ -170,6 +175,14 @@ class JvmMockKGateway : MockKGateway {
             }
         }
 
+        private var anyValueGenerator: AnyValueGenerator? = null
+        var anyValueGeneratorFactory: (voidInstance: Any) -> JvmAnyValueGenerator =
+            { voidInstance -> JvmAnyValueGenerator(voidInstance) }
+            set(value) {
+                anyValueGenerator = null
+                field = value
+            }
+
         val defaultImplementation = JvmMockKGateway()
         val defaultImplementationBuilder = { defaultImplementation }
     }

mockk/jvm/src/main/kotlin/io/mockk/impl/instantiation/JvmAnyValueGenerator.kt

@@ -2,7 +2,7 @@ package io.mockk.impl.instantiation
 
 import kotlin.reflect.KClass
 
-class JvmAnyValueGenerator(
+open class JvmAnyValueGenerator(
     private val voidInstance: Any
 ) : AnyValueGenerator() {
 

mockk/jvm/src/main/kotlin/io/mockk/impl/instantiation/JvmMockFactory.kt

@@ -51,7 +51,7 @@ class JvmMockFactory(
                                 "This can help if it's last call in the chain"
                     }
 
-                    gatewayAccess.anyValueGenerator.anyValue(cls, isNullable = false) {
+                    gatewayAccess.anyValueGenerator().anyValue(cls, isNullable = false) {
                         instantiator.instantiate(cls)
                     } as T
                 }

mockk/jvm/src/test/kotlin/io/mockk/it/NullableValueGeneratorTest.kt

@@ -0,0 +1,48 @@
+package io.mockk.it
+
+import io.mockk.impl.JvmMockKGateway
+import io.mockk.impl.instantiation.JvmAnyValueGenerator
+import io.mockk.mockk
+import kotlinx.coroutines.runBlocking
+import kotlin.reflect.KClass
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+@Suppress("UNUSED_PARAMETER")
+class NullableValueGeneratorTest {
+    class NullableValueGenerator(
+        voidInstance: Any
+    ) : JvmAnyValueGenerator(voidInstance) {
+        override fun anyValue(cls: KClass<*>, isNullable: Boolean, orInstantiateVia: () -> Any?): Any? {
+            if (isNullable) return null
+            return super.anyValue(cls, isNullable, orInstantiateVia)
+        }
+    }
+
+    @Test
+    fun testRelaxedMockReturnsNull() {
+        JvmMockKGateway.anyValueGeneratorFactory = { voidInstance ->
+            NullableValueGenerator(voidInstance)
+        }
+
+        class Bar
+
+        @Suppress("RedundantNullableReturnType", "RedundantSuspendModifier")
+        class Foo {
+            val property: Bar? = Bar()
+            val isEnabled: Boolean? = false
+            fun getSomething(): Bar? = Bar()
+            suspend fun getOtherThing(): Bar? = Bar()
+        }
+
+        val mock = mockk<Foo>(relaxed = true)
+        assertEquals(null, mock.property)
+        assertEquals(null, mock.isEnabled)
+        assertEquals(null, mock.getSomething())
+        assertEquals(null, runBlocking { mock.getOtherThing() })
+
+        JvmMockKGateway.anyValueGeneratorFactory = { voidInstance ->
+            JvmAnyValueGenerator(voidInstance)
+        }
+    }
+}