Consistent toString for MainCoroutineDispatcher implementations

So that is shows as "Dispatchers.Main" and "Dispatchers.Main.immediate"

kotlinx-coroutines-core/api/kotlinx-coroutines-core.api

@@ -446,6 +446,8 @@ public class kotlinx/coroutines/JobSupport : kotlinx/coroutines/ChildJob, kotlin
 public abstract class kotlinx/coroutines/MainCoroutineDispatcher : kotlinx/coroutines/CoroutineDispatcher {
  public fun <init> ()V
  public abstract fun getImmediate ()Lkotlinx/coroutines/MainCoroutineDispatcher;
+ public fun toString ()Ljava/lang/String;
+ protected final fun toStringInternalImpl ()Ljava/lang/String;
 }
 
 public final class kotlinx/coroutines/NonCancellable : kotlin/coroutines/AbstractCoroutineContextElement, kotlinx/coroutines/Job {

kotlinx-coroutines-core/common/src/MainCoroutineDispatcher.kt

@@ -43,4 +43,27 @@ public abstract class MainCoroutineDispatcher : CoroutineDispatcher() {
  * [Dispatchers.Main] supports immediate execution for Android, JavaFx and Swing platforms.
  */
  public abstract val immediate: MainCoroutineDispatcher
+
+ /**
+ * Returns a name of this main dispatcher for debugging purposes. This implementation returns
+ * `Dispatchers.Main` or `Dispatchers.Main.immediate` if it is the same as the corresponding
+ * reference in [Dispatchers] or a short class-name representation with address otherwise.
+ */
+ override fun toString(): String = toStringInternalImpl() ?: "$classSimpleName@$hexAddress"
+
+ /**
+ * Internal method for more specific [toString] implementations. It returns non-null
+ * string if this dispatcher is set in the platform as the main one.
+ * @suppress
+ */
+ @InternalCoroutinesApi
+ protected fun toStringInternalImpl(): String? {
+ val main = Dispatchers.Main
+ if (this === main) return "Dispatchers.Main"
+ val immediate =
+ try { main.immediate }
+ catch (e: UnsupportedOperationException) { null }
+ if (this === immediate) return "Dispatchers.Main.immediate"
+ return null
+ }
 }

kotlinx-coroutines-core/js/src/Dispatchers.kt

@@ -26,5 +26,5 @@ private class JsMainDispatcher(val delegate: CoroutineDispatcher) : MainCoroutin
 
  override fun dispatchYield(context: CoroutineContext, block: Runnable) = delegate.dispatchYield(context, block)
 
- override fun toString(): String = delegate.toString()
+ override fun toString(): String = toStringInternalImpl() ?: delegate.toString()
 }

kotlinx-coroutines-core/jvm/src/internal/MainDispatchers.kt

@@ -114,7 +114,7 @@ private class MissingMainCoroutineDispatcher(
  }
  }
 
- override fun toString(): String = "Main[missing${if (cause != null) ", cause=$cause" else ""}]"
+ override fun toString(): String = "Dispatchers.Main[missing${if (cause != null) ", cause=$cause" else ""}]"
 }
 
 /**

kotlinx-coroutines-core/jvm/test/DispatchersToStringTest.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2016-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines
+
+import kotlin.test.*
+
+class DispatchersToStringTest {
+ @Test
+ fun testStrings() {
+ assertEquals("Dispatchers.Unconfined", Dispatchers.Unconfined.toString())
+ assertEquals("Dispatchers.Default", Dispatchers.Default.toString())
+ assertEquals("Dispatchers.IO", Dispatchers.IO.toString())
+ assertEquals("Dispatchers.Main[missing]", Dispatchers.Main.toString())
+ assertEquals("Dispatchers.Main[missing]", Dispatchers.Main.immediate.toString())
+ }
+}

kotlinx-coroutines-core/native/src/Dispatchers.kt

@@ -26,5 +26,5 @@ private class NativeMainDispatcher(val delegate: CoroutineDispatcher) : MainCoro
 
  override fun dispatchYield(context: CoroutineContext, block: Runnable) = delegate.dispatchYield(context, block)
 
- override fun toString(): String = delegate.toString()
+ override fun toString(): String = toStringInternalImpl() ?: delegate.toString()
 }

ui/kotlinx-coroutines-android/src/HandlerDispatcher.kt

@@ -149,12 +149,13 @@ internal class HandlerContext private constructor(
  }
  }
 
- override fun toString(): String =
+ override fun toString(): String = toStringInternalImpl() ?: run {
  if (name != null) {
- if (invokeImmediately) "$name [immediate]" else name
+ if (invokeImmediately) "$name.immediate" else name
  } else {
  handler.toString()
  }
+ }
 
  override fun equals(other: Any?): Boolean = other is HandlerContext && other.handler === handler
  override fun hashCode(): Int = System.identityHashCode(handler)

ui/kotlinx-coroutines-android/test/HandlerDispatcherTest.kt

@@ -155,4 +155,10 @@ class HandlerDispatcherTest : TestBase() {
  yield() // yield back
  finish(5)
  }
+
+ @Test
+ fun testMainDispatcherToString() {
+ assertEquals("Dispatchers.Main", Dispatchers.Main.toString())
+ assertEquals("Dispatchers.Main.immediate", Dispatchers.Main.immediate.toString())
+ }
 }

ui/kotlinx-coroutines-javafx/src/JavaFxDispatcher.kt

@@ -70,7 +70,7 @@ private object ImmediateJavaFxDispatcher : JavaFxDispatcher() {
 
  override fun isDispatchNeeded(context: CoroutineContext): Boolean = !Platform.isFxApplicationThread()
 
- override fun toString() = "JavaFx [immediate]"
+ override fun toString() = toStringInternalImpl() ?: "JavaFx.immediate"
 }
 
 /**
@@ -85,7 +85,7 @@ internal object JavaFx : JavaFxDispatcher() {
  override val immediate: MainCoroutineDispatcher
  get() = ImmediateJavaFxDispatcher
 
- override fun toString() = "JavaFx"
+ override fun toString() = toStringInternalImpl() ?: "JavaFx"
 }
 
 private val pulseTimer by lazy {

ui/kotlinx-coroutines-javafx/test/JavaFxDispatcherTest.kt

@@ -7,6 +7,8 @@ package kotlinx.coroutines.javafx
 import javafx.application.*
 import kotlinx.coroutines.*
 import org.junit.*
+import org.junit.Test
+import kotlin.test.*
 
 class JavaFxDispatcherTest : TestBase() {
  @Before
@@ -56,4 +58,10 @@ class JavaFxDispatcherTest : TestBase() {
  finish(5)
  }
  }
+
+ @Test
+ fun testMainDispatcherToString() {
+ assertEquals("Dispatchers.Main", Dispatchers.Main.toString())
+ assertEquals("Dispatchers.Main.immediate", Dispatchers.Main.immediate.toString())
+ }
 }

ui/kotlinx-coroutines-swing/src/SwingDispatcher.kt

@@ -67,7 +67,7 @@ private object ImmediateSwingDispatcher : SwingDispatcher() {
 
  override fun isDispatchNeeded(context: CoroutineContext): Boolean = !SwingUtilities.isEventDispatchThread()
 
- override fun toString() = "Swing [immediate]"
+ override fun toString() = toStringInternalImpl() ?: "Swing.immediate"
 }
 
 /**
@@ -77,5 +77,5 @@ internal object Swing : SwingDispatcher() {
  override val immediate: MainCoroutineDispatcher
  get() = ImmediateSwingDispatcher
 
- override fun toString() = "Swing"
+ override fun toString() = toStringInternalImpl() ?: "Swing"
 }

ui/kotlinx-coroutines-swing/test/SwingTest.kt

@@ -97,4 +97,10 @@ class SwingTest : TestBase() {
  yield() // yield back
  finish(5)
  }
+
+ @Test
+ fun testMainDispatcherToString() {
+ assertEquals("Dispatchers.Main", Dispatchers.Main.toString())
+ assertEquals("Dispatchers.Main.immediate", Dispatchers.Main.immediate.toString())
+ }
 }