Consistent toString for MainCoroutineDispatcher implementations (Kotlin#2131)

So that is shows as "Dispatchers.Main" and "Dispatchers.Main.immediate".
Also remove hardcoded "Main" name in places of code where it is not needed anymore.

Author: elizarov

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

@@ -52,7 +52,7 @@ public sealed class HandlerDispatcher : MainCoroutineDispatcher(), Delay {
 internal class AndroidDispatcherFactory : MainDispatcherFactory {
 
     override fun createDispatcher(allFactories: List<MainDispatcherFactory>) =
-        HandlerContext(Looper.getMainLooper().asHandler(async = true), "Main")
+        HandlerContext(Looper.getMainLooper().asHandler(async = true))
 
     override fun hintOnError(): String? = "For tests Dispatchers.setMain from kotlinx-coroutines-test module can be used"
 
@@ -97,7 +97,7 @@ internal fun Looper.asHandler(async: Boolean): Handler {
 
 @JvmField
 @Deprecated("Use Dispatchers.Main instead", level = DeprecationLevel.HIDDEN)
-internal val Main: HandlerDispatcher? = runCatching { HandlerContext(Looper.getMainLooper().asHandler(async = true), "Main") }.getOrNull()
+internal val Main: HandlerDispatcher? = runCatching { HandlerContext(Looper.getMainLooper().asHandler(async = true)) }.getOrNull()
 
 /**
  * Implements [CoroutineDispatcher] on top of an arbitrary Android [Handler].
@@ -149,12 +149,10 @@ internal class HandlerContext private constructor(
         }
     }
 
-    override fun toString(): String =
-        if (name != null) {
-            if (invokeImmediately) "$name [immediate]" else name
-        } else {
-            handler.toString()
-        }
+    override fun toString(): String = toStringInternalImpl() ?: run {
+        val str = name ?: handler.toString()
+        if (invokeImmediately) "$str.immediate" else str
+    }
 
     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

@@ -123,8 +123,8 @@ class HandlerDispatcherTest : TestBase() {
         ReflectionHelpers.setStaticField(Build.VERSION::class.java, "SDK_INT", 28)
         val main = Looper.getMainLooper().asHandler(async = true).asCoroutineDispatcher("testName")
         assertEquals("testName", main.toString())
-        assertEquals("testName [immediate]", main.immediate.toString())
-        assertEquals("testName [immediate]", main.immediate.immediate.toString())
+        assertEquals("testName.immediate", main.immediate.toString())
+        assertEquals("testName.immediate", main.immediate.immediate.toString())
     }
 
     private suspend fun Job.join(mainLooper: ShadowLooper) {
@@ -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())
+    }
 }