Introduce CoroutineStackFrame interface for coroutine stack reconstruction in debugger

Fixes KT-26339

libraries/stdlib/coroutines/jvm/src/kotlin/coroutines/SafeContinuationJvm.kt

@@ -8,6 +8,7 @@ import java.util.concurrent.atomic.AtomicReferenceFieldUpdater
 import kotlin.*
 import kotlin.coroutines.intrinsics.CoroutineSingletons.*
 import kotlin.coroutines.intrinsics.COROUTINE_SUSPENDED
+import kotlin.coroutines.jvm.internal.CoroutineStackFrame
 
 @PublishedApi
 @SinceKotlin("1.3")
@@ -15,7 +16,7 @@ internal actual class SafeContinuation<in T>
 internal actual constructor(
     private val delegate: Continuation<T>,
     initialResult: Any?
-) : Continuation<T> {
+) : Continuation<T>, CoroutineStackFrame {
     @PublishedApi
     internal actual constructor(delegate: Continuation<T>) : this(delegate, UNDECIDED)
 
@@ -60,4 +61,15 @@ internal actual constructor(
             else -> result // either COROUTINE_SUSPENDED or data
         }
     }
+
+    // --- CoroutineStackFrame implementation
+
+    public override val callerFrame: CoroutineStackFrame?
+        get() = delegate as? CoroutineStackFrame
+
+    override fun getStackTraceElement(): StackTraceElement? =
+        null
+
+    override fun toString(): String =
+        "SafeContinuation for $delegate"
 }

libraries/stdlib/coroutines/jvm/src/kotlin/coroutines/jvm/internal/ContinuationImpl.kt

@@ -16,7 +16,7 @@ internal abstract class BaseContinuationImpl(
     // This is `public val` so that it is private on JVM and cannot be modified by untrusted code, yet
     // it has a public getter (since even untrusted code is allowed to inspect its call stack).
     public val completion: Continuation<Any?>?
-) : Continuation<Any?>, Serializable {
+) : Continuation<Any?>, CoroutineStackFrame, Serializable {
     // This implementation is final. This fact is used to unroll resumeWith recursion.
     public final override fun resumeWith(result: SuccessOrFailure<Any?>) {
         // Invoke "resume" debug probe only once, even if previous frames are "resumed" in the loop below, too
@@ -63,9 +63,16 @@ internal abstract class BaseContinuationImpl(
         throw UnsupportedOperationException("create(Any?;Continuation) has not been overridden")
     }
 
-    public override fun toString(): String {
-        return "Continuation at ${getStackTraceElement() ?: this::class.java.name}"
-    }
+    public override fun toString(): String =
+        "Continuation at ${getStackTraceElement() ?: this::class.java.name}"
+
+    // --- CoroutineStackFrame implementation
+    
+    public override val callerFrame: CoroutineStackFrame?
+        get() = completion as? CoroutineStackFrame
+
+    public override fun getStackTraceElement(): StackTraceElement? =
+        getStackTraceElementImpl()
 }
 
 @SinceKotlin("1.3")

libraries/stdlib/coroutines/jvm/src/kotlin/coroutines/jvm/internal/CoroutineStackFrame.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.coroutines.jvm.internal
+
+import kotlin.coroutines.*
+
+/**
+ * Represents one frame in the coroutine call stack for debugger.
+ * This interface is implemented by compiler-generated implementations of
+ * [Continuation] interface.
+ */
+public interface CoroutineStackFrame {
+    /**
+     * Returns a reference to the stack frame of the caller of this frame,
+     * that is a frame before this frame in coroutine call stack.
+     * The result is `null` for the first frame of coroutine.
+     */
+    public val callerFrame: CoroutineStackFrame?
+
+    /**
+     * Returns stack trace element that correspond to this stack frame.
+     * The result is `null` if the stack trace element is not available for this frame.
+     * In this case, the debugger represents this stack frame using the
+     * result of [toString] function.
+     */
+    public fun getStackTraceElement(): StackTraceElement?
+}

libraries/stdlib/coroutines/jvm/src/kotlin/coroutines/jvm/internal/DebugMetadata.kt

@@ -31,26 +31,30 @@ internal annotation class DebugMetadata(
  * The coroutine can be either running coroutine, that calls the function on its continuation and obtaining
  * the information about current file and line number, or, more likely, the function is called to produce accurate stack traces of
  * suspended coroutine.
+ *
+ * The result is `null` when debug metadata is not available.
  */
 @SinceKotlin("1.3")
 @JvmName("getStackTraceElement")
-internal fun BaseContinuationImpl.getStackTraceElement(): StackTraceElement? {
-    val debugMetadata = getDebugMetadataAnnotation()
+internal fun BaseContinuationImpl.getStackTraceElementImpl(): StackTraceElement? {
+    val debugMetadata = getDebugMetadataAnnotation() ?: return null
     val label = getLabel()
     val fileName = if (label < 0) "" else debugMetadata.sourceFiles[label]
     val lineNumber = if (label < 0) -1 else debugMetadata.lineNumbers[label]
     return StackTraceElement(debugMetadata.className, debugMetadata.methodName, fileName, lineNumber)
 }
 
-private fun BaseContinuationImpl.getDebugMetadataAnnotation(): DebugMetadata {
-    return javaClass.annotations.filterIsInstance<DebugMetadata>()[0]
-}
+private fun BaseContinuationImpl.getDebugMetadataAnnotation(): DebugMetadata? =
+    javaClass.getAnnotation(DebugMetadata::class.java)
 
-private fun BaseContinuationImpl.getLabel(): Int {
-    val field = javaClass.getDeclaredField("label") ?: return -1
-    field.isAccessible = true
-    return (field.get(this) as? Int ?: 0) - 1
-}
+private fun BaseContinuationImpl.getLabel(): Int =
+    try {
+        val field = javaClass.getDeclaredField("label")
+        field.isAccessible = true
+        (field.get(this) as? Int ?: 0) - 1
+    } catch (e: Exception) { // NoSuchFieldException, SecurityException, or IllegalAccessException
+        -1
+    }
 
 /**
  * Returns an array of spilled variable names and continuation's field names where the variable has been spilled.
@@ -60,10 +64,13 @@ private fun BaseContinuationImpl.getLabel(): Int {
  *
  * The function is for debugger to use, thus it returns simplest data type possible.
  * This function should only be called on suspended coroutines to get accurate mapping.
+ *
+ * The result is `null` when debug metadata is not available.
  */
 @SinceKotlin("1.3")
-internal fun BaseContinuationImpl.getSpilledVariableFieldMapping(): Array<String> {
-    val debugMetadata = getDebugMetadataAnnotation()
+@JvmName("getSpilledVariableFieldMapping")
+internal fun BaseContinuationImpl.getSpilledVariableFieldMapping(): Array<String>? {
+    val debugMetadata = getDebugMetadataAnnotation() ?: return null
     val res = arrayListOf<String>()
     val label = getLabel()
     for ((i, labelOfIndex) in debugMetadata.indexToLabel.withIndex()) {

libraries/stdlib/coroutines/jvm/test/DebugMetadataTest.kt

@@ -46,18 +46,18 @@ class DebugMetadataTest {
             StackTraceElement("SomeClass", "testMethod", "test.kt", 10),
             myContinuation.getStackTraceElement()
         )
-        assertEquals(listOf("L$1", "a", "L$2", "b"), myContinuation.getSpilledVariableFieldMapping().toList())
+        assertEquals(listOf("L$1", "a", "L$2", "b"), myContinuation.getSpilledVariableFieldMapping()!!.toList())
         myContinuation.label = 2
         assertEquals(
             StackTraceElement("SomeClass", "testMethod", "test1.kt", 2),
             myContinuation.getStackTraceElement()
         )
-        assertEquals(listOf("L$1", "b", "L$2", "c"), myContinuation.getSpilledVariableFieldMapping().toList())
+        assertEquals(listOf("L$1", "b", "L$2", "c"), myContinuation.getSpilledVariableFieldMapping()!!.toList())
         myContinuation.label = 3
         assertEquals(
             StackTraceElement("SomeClass", "testMethod", "test.kt", 11),
             myContinuation.getStackTraceElement()
         )
-        assertEquals(listOf("L$1", "c"), myContinuation.getSpilledVariableFieldMapping().toList())
+        assertEquals(listOf("L$1", "c"), myContinuation.getSpilledVariableFieldMapping()!!.toList())
     }
 }