APIs for easier freeze debugging. (#1783)

backend.native/tests/build.gradle

@@ -692,6 +692,12 @@ task freeze3(type: RunKonanTest) {
     source = "runtime/workers/freeze3.kt"
 }
 
+task freeze4(type: RunKonanTest) {
+    disabled = (project.testTarget == 'wasm32') // No exceptions on WASM.
+    goldValue = "OK\n"
+    source = "runtime/workers/freeze4.kt"
+}
+
 task atomic0(type: RunKonanTest) {
     disabled = (project.testTarget == 'wasm32') // Workers need pthreads.
     goldValue = "35\n" + "20\n" + "OK\n"

backend.native/tests/runtime/workers/freeze4.kt

@@ -0,0 +1,24 @@
+package runtime.workers.freeze4
+
+import kotlin.test.*
+
+import konan.worker.*
+
+data class Data(val x: Int, val s: String, val next: Data? = null)
+
+@Test fun runTest() {
+    val data1 = Data(1, "")
+    data1.freeze()
+    assertFailsWith<FreezingException> {
+        data1.ensureNeverFrozen()
+    }
+
+    val dataNF = Data(42, "42")
+    dataNF.ensureNeverFrozen()
+    val data2 = Data(2, "2", dataNF)
+    assertFailsWith<FreezingException> {
+        data2.freeze()
+    }
+    assert(!data2.isFrozen)
+    println("OK")
+}