Use toString implementation for continuations to leverage debug metadata

Fixes #679

Author: qwwdfsad

core/kotlinx-coroutines-core/src/Debug.kt

@@ -41,17 +41,9 @@ internal val DEBUG = systemProp(DEBUG_PROPERTY_NAME).let { value ->
 internal actual val Any.hexAddress: String
     get() = Integer.toHexString(System.identityHashCode(this))
 
-internal fun Any?.toSafeString(): String =
-    try { toString() }
-    catch (e: Throwable) { "toString() failed with $e" }
-
-// **KLUDGE**: there is no reason to include continuation into debug string until the following ticket is resolved:
-// KT-18986 Debug-friendly toString implementation for CoroutineImpl
-// (the current string representation of continuation is useless and uses buggy reflection internals)
-// So, this function is a replacement that extract a usable information from continuation -> its class name, at least
 internal actual fun Continuation<*>.toDebugString(): String = when (this) {
     is DispatchedContinuation -> toString()
-    else -> "${this::class.java.name}@$hexAddress"
+    else -> "$this@$hexAddress"
 }
 
 internal actual val Any.classSimpleName: String get() = this::class.java.simpleName

core/kotlinx-coroutines-core/test/CancellableContinuationJvmTest.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines
+
+import kotlin.coroutines.*
+import kotlin.test.*
+
+class CancellableContinuationJvmTest : TestBase() {
+    @Test
+    fun testToString() = runTest {
+        checkToString()
+    }
+
+    private suspend fun checkToString() {
+        suspendCancellableCoroutine<Unit> {
+            it.resume(Unit)
+            assertTrue(it.toString().contains("kotlinx/coroutines/CancellableContinuationJvmTest.checkToString(CancellableContinuationJvmTest.kt:16"))
+        }
+    }
+}