Add workaround for androidx toolchain issues: try to load main dispat… (#709)

Embed proguard rules to JAR resources to workaround Androidx issue with ServiceLoader, update documentation

Fixes #657

Author: qwwdfsad

README.md

@@ -129,17 +129,9 @@ coroutine dispatcher and also makes sure that in case of crashed coroutine with
 exception is logged before crashing Android application, similarly to the way uncaught exceptions in 
 threads are handled by Android runtime. 
 
-### ProGuard
+### R8 and ProGuard
 
-In obfuscated code, fields with different types can have the same names,
-and `AtomicReferenceFieldUpdater` may be unable to find the correct ones.
-To avoid field overloading by type during obfuscation, add this to your config:
-
-```
--keepclassmembernames class kotlinx.** {
-    volatile <fields>;
-}
-```
+If you are using R8 or ProGuard add the options from [coroutines.pro](core/kotlinx-coroutines-core/resources/META-INF/proguard/coroutines.pro) file to your rules.
 
 ## Building 
 

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

@@ -4,7 +4,6 @@
 
 package kotlinx.coroutines
 
-import kotlinx.coroutines.internal.*
 import kotlin.coroutines.*
 
 internal expect fun handleCoroutineExceptionImpl(context: CoroutineContext, exception: Throwable)

core/kotlinx-coroutines-core/resources/META-INF/proguard/coroutines.pro

@@ -0,0 +1,8 @@
+# ServiceLoader support
+-keepnames class kotlinx.coroutines.internal.MainDispatcherFactory {}
+-keepnames class kotlinx.coroutines.CoroutineExceptionHandler {}
+
+# Most of volatile fields are updated with AFU and should not be mangled
+-keepclassmembernames class kotlinx.** {
+    volatile <fields>;
+}

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

@@ -8,8 +8,8 @@ package kotlinx.coroutines
 
 import kotlinx.coroutines.internal.*
 import kotlinx.coroutines.scheduling.*
-import kotlin.coroutines.*
 import java.util.*
+import kotlin.coroutines.*
 
 /**
  * Name of the property that defines the maximal number of threads that are used by [Dispatchers.IO] coroutines dispatcher.
@@ -20,7 +20,6 @@ public const val IO_PARALLELISM_PROPERTY_NAME = "kotlinx.coroutines.io.paralleli
  * Groups various implementations of [CoroutineDispatcher].
  */
 public actual object Dispatchers {
-
     /**
      * The default [CoroutineDispatcher] that is used by all standard builders like
      * [launch][CoroutineScope.launch], [async][CoroutineScope.async], etc

ui/kotlinx-coroutines-android/animation-app/app/proguard-rules.pro

@@ -1,3 +1,5 @@
+-keepnames class kotlinx.coroutines.internal.MainDispatcherFactory {}
+-keepnames class kotlinx.coroutines.CoroutineExceptionHandler {}
 -keepclassmembernames class kotlinx.** {
     volatile <fields>;
 }

ui/kotlinx-coroutines-android/example-app/app/proguard-rules.pro

@@ -1,3 +1,5 @@
+-keepnames class kotlinx.coroutines.internal.MainDispatcherFactory {}
+-keepnames class kotlinx.coroutines.CoroutineExceptionHandler {}
 -keepclassmembernames class kotlinx.** {
     volatile <fields>;
 }

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

@@ -33,6 +33,11 @@ public sealed class HandlerDispatcher : MainCoroutineDispatcher(), Delay {
 
 @Keep
 internal class AndroidDispatcherFactory : MainDispatcherFactory {
+    companion object {
+        @JvmStatic // accessed reflectively from core
+        fun getDispatcher(): MainCoroutineDispatcher = Main
+    }
+
     override fun createDispatcher(): MainCoroutineDispatcher = Main
 
     override val loadPriority: Int