Make the code build without changes to the core module

Author: dkhalanskyjb

kotlinx-coroutines-core/build.gradle

@@ -81,7 +81,7 @@ kotlin {
         }
         languageSettings {
             progressiveMode = true
-            optInAnnotations.each { useExperimentalAnnotation(it) }
+            optInAnnotations.each { optIn(it) }
         }
     }
 

kotlinx-coroutines-core/common/src/internal/MainDispatchers.kt renamed to kotlinx-coroutines-core/jvm/src/internal/MainDispatchers.kt

@@ -5,8 +5,45 @@
 package kotlinx.coroutines.internal
 
 import kotlinx.coroutines.*
+import java.util.*
 import kotlin.coroutines.*
 
+/**
+ * Name of the boolean property that enables using of [FastServiceLoader].
+ */
+private const val FAST_SERVICE_LOADER_PROPERTY_NAME = "kotlinx.coroutines.fast.service.loader"
+
+// Lazy loader for the main dispatcher
+internal object MainDispatcherLoader {
+
+    private val FAST_SERVICE_LOADER_ENABLED = systemProp(FAST_SERVICE_LOADER_PROPERTY_NAME, true)
+
+    @JvmField
+    val dispatcher: MainCoroutineDispatcher = loadMainDispatcher()
+
+    private fun loadMainDispatcher(): MainCoroutineDispatcher {
+        return try {
+            val factories = if (FAST_SERVICE_LOADER_ENABLED) {
+                FastServiceLoader.loadMainDispatcherFactory()
+            } else {
+                // We are explicitly using the
+                // `ServiceLoader.load(MyClass::class.java, MyClass::class.java.classLoader).iterator()`
+                // form of the ServiceLoader call to enable R8 optimization when compiled on Android.
+                ServiceLoader.load(
+                        MainDispatcherFactory::class.java,
+                        MainDispatcherFactory::class.java.classLoader
+                ).iterator().asSequence().toList()
+            }
+            @Suppress("ConstantConditionIf")
+            factories.maxByOrNull { it.loadPriority }?.tryCreateDispatcher(factories)
+                ?: createMissingDispatcher()
+        } catch (e: Throwable) {
+            // Service loader can throw an exception as well
+            createMissingDispatcher(e)
+        }
+    }
+}
+
 /**
  * If anything goes wrong while trying to create main dispatcher (class not found,
  * initialization failed, etc), then replace the main dispatcher with a special
@@ -34,7 +71,7 @@ private val SUPPORT_MISSING = true
     "ConstantConditionIf",
     "IMPLICIT_NOTHING_TYPE_ARGUMENT_AGAINST_NOT_NOTHING_EXPECTED_TYPE" // KT-47626
 )
-internal fun createMissingDispatcher(cause: Throwable? = null, errorHint: String? = null): MainCoroutineDispatcher =
+private fun createMissingDispatcher(cause: Throwable? = null, errorHint: String? = null) =
     if (SUPPORT_MISSING) MissingMainCoroutineDispatcher(cause, errorHint) else
         cause?.let { throw it } ?: throwMissingMainDispatcherException()
 

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

@@ -19,7 +19,7 @@ kotlin {
             resources.srcDir("$platform/test-resources")
         }
         languageSettings {
-            experimentalAnnotations.forEach { useExperimentalAnnotation(it) }
+            experimentalAnnotations.forEach { optIn(it) }
         }
     }
 }

kotlinx-coroutines-test/build.gradle.kts

@@ -1,14 +1,10 @@
 /*
  * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
  */
-@file:Suppress("unused")
-@file:JvmName("TestDispatchers")
 
 package kotlinx.coroutines.test
 
 import kotlinx.coroutines.*
-import kotlinx.coroutines.test.internal.*
-import kotlin.jvm.*
 
 /**
  * Sets the given [dispatcher] as an underlying dispatcher of [Dispatchers.Main].
@@ -17,12 +13,7 @@ import kotlin.jvm.*
  * It is unsafe to call this method if alive coroutines launched in [Dispatchers.Main] exist.
  */
 @ExperimentalCoroutinesApi
-public fun Dispatchers.setMain(dispatcher: CoroutineDispatcher) {
-    require(dispatcher !is TestMainDispatcher) { "Dispatchers.setMain(Dispatchers.Main) is prohibited, probably Dispatchers.resetMain() should be used instead" }
-    val mainDispatcher = Main
-    require(mainDispatcher is TestMainDispatcher) { "TestMainDispatcher is not set as main dispatcher, have $mainDispatcher instead." }
-    mainDispatcher.setDispatcher(dispatcher)
-}
+public expect fun Dispatchers.setMain(dispatcher: CoroutineDispatcher)
 
 /**
  * Resets state of the [Dispatchers.Main] to the original main dispatcher.
@@ -32,8 +23,4 @@ public fun Dispatchers.setMain(dispatcher: CoroutineDispatcher) {
  * It is unsafe to call this method if alive coroutines launched in [Dispatchers.Main] exist.
  */
 @ExperimentalCoroutinesApi
-public fun Dispatchers.resetMain() {
-    val mainDispatcher = Main
-    require(mainDispatcher is TestMainDispatcher) { "TestMainDispatcher is not set as main dispatcher, have $mainDispatcher instead." }
-    mainDispatcher.resetDispatcher()
-}
+public expect fun Dispatchers.resetMain()

kotlinx-coroutines-test/common/src/TestDispatchers.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.test
+import kotlinx.coroutines.*
+
+@ExperimentalCoroutinesApi
+public actual fun Dispatchers.setMain(dispatcher: CoroutineDispatcher) {
+    throw UnsupportedOperationException("`setMain` is not supported on JS")
+}
+
+@ExperimentalCoroutinesApi
+public actual fun Dispatchers.resetMain() {
+    throw UnsupportedOperationException("`resetMain` is not supported on JS")
+}

kotlinx-coroutines-test/js/src/TestDispatchers.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+@file:JvmName("TestDispatchers")
+
+package kotlinx.coroutines.test
+
+import kotlinx.coroutines.*
+import kotlinx.coroutines.test.internal.*
+
+@ExperimentalCoroutinesApi
+public actual fun Dispatchers.setMain(dispatcher: CoroutineDispatcher) {
+    require(dispatcher !is TestMainDispatcher) { "Dispatchers.setMain(Dispatchers.Main) is prohibited, probably Dispatchers.resetMain() should be used instead" }
+    val mainDispatcher = Main
+    require(mainDispatcher is TestMainDispatcher) { "TestMainDispatcher is not set as main dispatcher, have $mainDispatcher instead." }
+    mainDispatcher.setDispatcher(dispatcher)
+}
+
+@ExperimentalCoroutinesApi
+public actual fun Dispatchers.resetMain() {
+    val mainDispatcher = Main
+    require(mainDispatcher is TestMainDispatcher) { "TestMainDispatcher is not set as main dispatcher, have $mainDispatcher instead." }
+    mainDispatcher.resetDispatcher()
+}

kotlinx-coroutines-test/jvm/src/TestDispatchers.kt

@@ -0,0 +1,17 @@
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.test
+
+import kotlinx.coroutines.*
+
+@ExperimentalCoroutinesApi
+public actual fun Dispatchers.setMain(dispatcher: CoroutineDispatcher) {
+    throw UnsupportedOperationException("`setMain` is not supported on Native")
+}
+
+@ExperimentalCoroutinesApi
+public actual fun Dispatchers.resetMain() {
+    throw UnsupportedOperationException("`resetMain` is not supported on Native")
+}