Remove intrinsics usage in RibCoroutineWorker

This commit changes dispatching logic to a much simpler one that does not require usage of intrinsics.

In order to synchronously get an instance of `bindJob`, we start the `unbindJob` coroutine undispatched (`bindJob` is a child of `unbindJob`, so we need an instance of `unbindJob` to create an instance of `bindJob`).

After saving `bindJob`, we properly dispatch in a cancellable way by simply `launch`ing a new coroutine.

Author: psteiger

android/libraries/rib-base/src/main/kotlin/com/uber/rib/core/RibCoroutineWorker.kt

@@ -16,20 +16,10 @@
 package com.uber.rib.core
 
 import com.uber.autodispose.coroutinesinterop.asScopeProvider
-import kotlin.contracts.ExperimentalContracts
-import kotlin.contracts.InvocationKind
-import kotlin.contracts.contract
-import kotlin.coroutines.ContinuationInterceptor
 import kotlin.coroutines.CoroutineContext
 import kotlin.coroutines.EmptyCoroutineContext
-import kotlin.coroutines.coroutineContext
-import kotlin.coroutines.intrinsics.COROUTINE_SUSPENDED
-import kotlin.coroutines.intrinsics.intercepted
-import kotlin.coroutines.intrinsics.suspendCoroutineUninterceptedOrReturn
-import kotlin.coroutines.resume
 import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.CompletableJob
-import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.CoroutineStart
 import kotlinx.coroutines.Job
@@ -122,10 +112,17 @@ public fun CoroutineScope.bind(
   worker: RibCoroutineWorker,
   context: CoroutineContext = RibDispatchers.Default,
 ): BindWorkerHandle {
-  val bindJob: CompletableJob // A job that completes once worker's onStart completes
+  var bindJob: CompletableJob? = null // A job that completes once worker's onStart completes
   val unbindJob =
-    launch(context, { bindJob = createBindingJob() }) { bindAndAwaitCancellation(worker, bindJob) }
-  return BindWorkerHandleImpl(bindJob, unbindJob)
+    launch(context, CoroutineStart.UNDISPATCHED) {
+      val job = createBindingJob()
+      bindJob = job
+      // launch again -- this time, we will dispatch if installed dispatcher
+      // tell us to (CoroutineDispatcher.isDispatchNeeded()).
+      launch { bindAndAwaitCancellation(worker, job) }
+    }
+  // !! is safe here -- outer coroutine was started undispatched.
+  return BindWorkerHandleImpl(bindJob!!, unbindJob)
 }
 
 /** Binds [workers] in a scope that is a child of the [CoroutineScope] receiver. */
@@ -139,46 +136,6 @@ public fun CoroutineScope.bind(
   }
 }
 
-/**
- * Guarantees to run synchronous [init] block exactly once in an undispatched manner.
- *
- * **Exceptions thrown in [init] block will be rethrown at call site.**
- */
-@OptIn(ExperimentalContracts::class)
-private fun CoroutineScope.launch(
-  context: CoroutineContext = EmptyCoroutineContext,
-  init: CoroutineScope.() -> Unit = {},
-  block: suspend CoroutineScope.() -> Unit,
-): Job {
-  contract {
-    callsInPlace(init, InvocationKind.EXACTLY_ONCE)
-    callsInPlace(block, InvocationKind.AT_MOST_ONCE)
-  }
-  var initError: Throwable? = null
-  val job =
-    launch(context, CoroutineStart.UNDISPATCHED) {
-      runCatching(init).onFailure { initError = it }.getOrThrow()
-      dispatchIfNeeded()
-      block()
-    }
-  initError?.let { throw it }
-  return job
-}
-
-private suspend inline fun dispatchIfNeeded() {
-  suspendCoroutineUninterceptedOrReturn sc@{ cont ->
-    val context = cont.context
-    val dispatcher = context[ContinuationInterceptor] as CoroutineDispatcher
-    if (!dispatcher.isDispatchNeeded(context)) return@sc Unit
-    // Coroutine was not in the right context -- we'll dispatch.
-    context.ensureActive()
-    cont.intercepted().resume(Unit)
-    COROUTINE_SUSPENDED
-  }
-  // Don't continue if coroutine was cancelled after returning from dispatch.
-  coroutineContext.ensureActive()
-}
-
 private fun CoroutineScope.createBindingJob(): CompletableJob =
   Job(coroutineContext.job).also {
     // Cancel `unbindJob` if `bindJob` has cancelled. This is important to abort `onStart` if

android/libraries/rib-base/src/test/kotlin/com/uber/rib/core/RibCoroutineWorkerTest.kt

@@ -208,15 +208,18 @@ class RibCoroutineWorkerTest {
     val router = mock<Router<*>>()
     val interactor = object : Interactor<Any, Router<*>>() {}
     val subject = PublishSubject.create<Unit>()
+    var started = false
     var disposed = false
-    val ribCoroutineWorker = RibCoroutineWorker {
-      subject.doOnDispose { disposed = true }.autoDispose(this).subscribe()
+    val ribCoroutineWorker = RibCoroutineWorker { scope ->
+      started = true
+      subject.doOnDispose { disposed = true }.autoDispose(scope).subscribe()
     }
     val worker = ribCoroutineWorker.asWorker()
     InteractorHelper.attach(interactor, Any(), router, null)
     val unbinder = WorkerBinder.bind(interactor, worker)
     runCurrent()
     subject.onNext(Unit)
+    assertThat(started).isTrue()
     assertThat(disposed).isFalse()
     unbinder.unbind()
     runCurrent()