Revert some of the debug snapshotting stuff to prep for a better approach.

Reverts 2 commits:

- Revert "Step 2/2: Introduce diagnostics for workflow outputs."
  This reverts commit 29bae34.
- Revert "Step 1/2: Introduce debug snapshots for emitting diagnostic information about the workflow tree."
  This reverts commit 1cee014.

Author: zach-klippenstein

kotlin/samples/tictactoe/app/src/main/java/com/squareup/sample/mainactivity/MainActivity.kt

@@ -24,7 +24,6 @@ import com.squareup.sample.panel.PanelContainer
 import com.squareup.workflow.ui.ViewRegistry
 import com.squareup.workflow.ui.WorkflowRunner
 import com.squareup.workflow.ui.setContentWorkflow
-import io.reactivex.disposables.CompositeDisposable
 import io.reactivex.disposables.Disposables
 import timber.log.Timber
 
@@ -53,10 +52,7 @@ class MainActivity : AppCompatActivity() {
       finish()
     }
 
-    loggingSub = CompositeDisposable(
-        workflowRunner.renderings.subscribe { Timber.d("rendering: %s", it) },
-        workflowRunner.debugInfo.subscribe { Timber.v("debug snapshot: %s", it) }
-    )
+    loggingSub = workflowRunner.renderings.subscribe { Timber.d("rendering: %s", it) }
   }
 
   override fun onSaveInstanceState(outState: Bundle) {

kotlin/workflow-runtime/src/main/java/com/squareup/workflow/LaunchWorkflow.kt

@@ -15,7 +15,6 @@
  */
 package com.squareup.workflow
 
-import com.squareup.workflow.debugging.WorkflowDebugInfo
 import com.squareup.workflow.internal.RealWorkflowLoop
 import com.squareup.workflow.internal.WorkflowLoop
 import com.squareup.workflow.internal.unwrapCancellationCause
@@ -152,15 +151,10 @@ internal fun <PropsT, StateT, OutputT : Any, RenderingT, RunnerT> launchWorkflow
 ): RunnerT {
   val renderingsAndSnapshots = ConflatedBroadcastChannel<RenderingAndSnapshot<RenderingT>>()
   val outputs = BroadcastChannel<OutputT>(capacity = 1)
-  val debugSnapshots = ConflatedBroadcastChannel<WorkflowDebugInfo>()
   val workflowScope = scope + Job(parent = scope.coroutineContext[Job])
 
   // Give the caller a chance to start collecting outputs.
-  val session = WorkflowSession(
-      renderingsAndSnapshots.asFlow(),
-      outputs.asFlow(),
-      debugSnapshots.asFlow()
-  )
+  val session = WorkflowSession(renderingsAndSnapshots.asFlow(), outputs.asFlow())
   val result = beforeStart(workflowScope, session)
 
   val workflowJob = workflowScope.launch {
@@ -171,8 +165,7 @@ internal fun <PropsT, StateT, OutputT : Any, RenderingT, RunnerT> launchWorkflow
         initialSnapshot = initialSnapshot,
         initialState = initialState,
         onRendering = renderingsAndSnapshots::send,
-        onOutput = outputs::send,
-        onDebugSnapshot = debugSnapshots::send
+        onOutput = outputs::send
     )
   }
 
@@ -183,7 +176,6 @@ internal fun <PropsT, StateT, OutputT : Any, RenderingT, RunnerT> launchWorkflow
     val realCause = cause?.unwrapCancellationCause()
     renderingsAndSnapshots.close(realCause)
     outputs.close(realCause)
-    debugSnapshots.close(realCause)
 
     // If the cancellation came from inside the workflow loop, the outer runtime scope needs to be
     // explicitly cancelled. See https://github.com/square/workflow/issues/464.

kotlin/workflow-runtime/src/main/java/com/squareup/workflow/WorkflowSession.kt

@@ -15,18 +15,14 @@
  */
 package com.squareup.workflow
 
-import com.squareup.workflow.debugging.WorkflowDebugInfo
 import kotlinx.coroutines.flow.Flow
 
 /**
  * A tuple of [Flow]s representing all the emissions from the workflow runtime.
  *
  * Passed to the function taken by [launchWorkflowIn].
- *
- * @param debugInfo A stream of [diagnostic information][WorkflowDebugInfo] about the runtime.
  */
 class WorkflowSession<out OutputT : Any, out RenderingT>(
   val renderingsAndSnapshots: Flow<RenderingAndSnapshot<RenderingT>>,
-  val outputs: Flow<OutputT>,
-  val debugInfo: Flow<WorkflowDebugInfo>
+  val outputs: Flow<OutputT>
 )

kotlin/workflow-runtime/src/main/java/com/squareup/workflow/debugging/WorkflowDebugInfo.kt

@@ -18,7 +18,6 @@ package com.squareup.workflow.internal
 import com.squareup.workflow.Worker
 import com.squareup.workflow.Workflow
 import com.squareup.workflow.WorkflowAction
-import com.squareup.workflow.debugging.WorkflowHierarchyDebugSnapshot.Child
 import kotlinx.coroutines.Deferred
 
 /**
@@ -30,7 +29,6 @@ import kotlinx.coroutines.Deferred
  */
 data class Behavior<StateT, out OutputT : Any> internal constructor(
   val childCases: List<WorkflowOutputCase<*, *, StateT, OutputT>>,
-  val childDebugSnapshots: List<Child>,
   val workerCases: List<WorkerCase<*, StateT, OutputT>>,
   val nextActionFromEvent: Deferred<WorkflowAction<StateT, OutputT>>
 ) {

kotlin/workflow-runtime/src/main/java/com/squareup/workflow/internal/Behavior.kt

@@ -23,7 +23,6 @@ import com.squareup.workflow.Sink
 import com.squareup.workflow.Worker
 import com.squareup.workflow.Workflow
 import com.squareup.workflow.WorkflowAction
-import com.squareup.workflow.debugging.WorkflowHierarchyDebugSnapshot.Child
 import com.squareup.workflow.internal.Behavior.WorkerCase
 import com.squareup.workflow.internal.Behavior.WorkflowOutputCase
 import kotlinx.coroutines.CompletableDeferred
@@ -43,13 +42,12 @@ class RealRenderContext<StateT, OutputT : Any>(
       child: Workflow<ChildPropsT, ChildOutputT, ChildRenderingT>,
       id: WorkflowId<ChildPropsT, ChildOutputT, ChildRenderingT>,
       props: ChildPropsT
-    ): RenderingEnvelope<ChildRenderingT>
+    ): ChildRenderingT
   }
 
   private val nextUpdateFromEvent = CompletableDeferred<WorkflowAction<StateT, OutputT>>()
   private val workerCases = mutableListOf<WorkerCase<*, StateT, OutputT>>()
   private val childCases = mutableListOf<WorkflowOutputCase<*, *, StateT, OutputT>>()
-  private val childDebugSnapshots = mutableListOf<Child>()
 
   /** Used to prevent modifications to this object after [buildBehavior] is called. */
   private var frozen = false
@@ -95,11 +93,7 @@ class RealRenderContext<StateT, OutputT : Any>(
     val case: WorkflowOutputCase<ChildPropsT, ChildOutputT, StateT, OutputT> =
       WorkflowOutputCase(child, id, props, handler)
     childCases += case
-    val (rendering, debugSnapshot) = renderer.render(case, child, id, props)
-    // Hold onto the description of this child's state for later, so we can include it in the
-    // parent's debug snapshot tree.
-    childDebugSnapshots += Child(key, debugSnapshot)
-    return rendering
+    return renderer.render(case, child, id, props)
   }
 
   override fun <T> runningWorker(
@@ -119,7 +113,6 @@ class RealRenderContext<StateT, OutputT : Any>(
     frozen = true
     return Behavior(
         childCases = childCases.toList(),
-        childDebugSnapshots = childDebugSnapshots.toList(),
         workerCases = workerCases.toList(),
         nextActionFromEvent = nextUpdateFromEvent
     )

kotlin/workflow-runtime/src/main/java/com/squareup/workflow/internal/OutputEnvelope.kt

@@ -19,9 +19,6 @@ import com.squareup.workflow.Snapshot
 import com.squareup.workflow.StatefulWorkflow
 import com.squareup.workflow.Workflow
 import com.squareup.workflow.WorkflowAction
-import com.squareup.workflow.WorkflowAction.Companion.noAction
-import com.squareup.workflow.debugging.WorkflowUpdateDebugInfo.Kind
-import com.squareup.workflow.debugging.WorkflowUpdateDebugInfo.Source
 import com.squareup.workflow.internal.Behavior.WorkflowOutputCase
 import com.squareup.workflow.parse
 import com.squareup.workflow.readByteStringWithLength
@@ -62,7 +59,7 @@ internal class SubtreeManager<StateT, OutputT : Any>(
         child: Workflow<ChildPropsT, ChildOutputT, ChildRenderingT>,
         id: WorkflowId<ChildPropsT, ChildOutputT, ChildRenderingT>,
         props: ChildPropsT
-      ): RenderingEnvelope<ChildRenderingT> {
+      ): ChildRenderingT {
   // @formatter:on
     // Start tracking this case so we can be ready to render it.
     @Suppress("UNCHECKED_CAST")
@@ -83,36 +80,15 @@ internal class SubtreeManager<StateT, OutputT : Any>(
   /**
    * Uses [selector] to invoke [WorkflowNode.tick] for every running child workflow this instance
    * is managing.
-   *
-   * If one of this workflow's children emits an output, [handler] will be called with the action
-   * assigned to that workflow and a [Source.Subtree] describing the child that triggered the
-   * update.
-   *
-   * Note that if [handler] is called with [Kind.Passthrough], the workflow action that gets
-   * passed in will always be [noAction]. This is the only logical value because
-   * [Kind.Passthrough] specifically means that this workflow did not actually get updated
-   * itself, but one of its descendants did and this one is just part of the path down the tree.
    */
   fun <T : Any> tickChildren(
-    selector: SelectBuilder<OutputEnvelope<T>>,
-    handler: (WorkflowAction<StateT, OutputT>, Kind) -> OutputEnvelope<T>
+    selector: SelectBuilder<T?>,
+    handler: (WorkflowAction<StateT, OutputT>) -> T?
   ) {
     for ((case, host) in hostLifetimeTracker.lifetimes) {
       host.tick(selector) { output ->
-        return@tick if (output.output != null) {
-          val componentUpdate = case.acceptChildOutput(output.output)
-          // This workflow's child emitted a non-null output: the WorkflowNode will execute the
-          // WorkflowAction, and we need to pass DidUpdate to indicate that this workflow actually
-          // got updated.
-          handler(
-              componentUpdate,
-              Kind.Updated(Source.Subtree(case.id.name, output.output, output.debugInfo))
-          )
-        } else {
-          // The child didn't actually emit an output, which means this workflow has nothing to do,
-          // which means we will only report our child updating.
-          handler(noAction(), Kind.Passthrough(case.id.name, output.debugInfo))
-        }
+        val componentUpdate = case.acceptChildOutput(output)
+        return@tick handler(componentUpdate)
       }
     }
   }

kotlin/workflow-runtime/src/main/java/com/squareup/workflow/internal/RealRenderContext.kt

@@ -18,7 +18,6 @@ package com.squareup.workflow.internal
 import com.squareup.workflow.RenderingAndSnapshot
 import com.squareup.workflow.Snapshot
 import com.squareup.workflow.StatefulWorkflow
-import com.squareup.workflow.debugging.WorkflowDebugInfo
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.FlowPreview
 import kotlinx.coroutines.channels.consume
@@ -44,8 +43,7 @@ internal interface WorkflowLoop {
     initialSnapshot: Snapshot?,
     initialState: StateT? = null,
     onRendering: suspend (RenderingAndSnapshot<RenderingT>) -> Unit,
-    onOutput: suspend (OutputT) -> Unit,
-    onDebugSnapshot: suspend (WorkflowDebugInfo) -> Unit
+    onOutput: suspend (OutputT) -> Unit
   ): Nothing
 }
 
@@ -58,12 +56,11 @@ internal object RealWorkflowLoop : WorkflowLoop {
     initialSnapshot: Snapshot?,
     initialState: StateT?,
     onRendering: suspend (RenderingAndSnapshot<RenderingT>) -> Unit,
-    onOutput: suspend (OutputT) -> Unit,
-    onDebugSnapshot: suspend (WorkflowDebugInfo) -> Unit
+    onOutput: suspend (OutputT) -> Unit
   ): Nothing = coroutineScope {
     val inputsChannel = props.produceIn(this)
     inputsChannel.consume {
-      var output: OutputEnvelope<OutputT>? = null
+      var output: OutputT? = null
       var input: PropsT = inputsChannel.receive()
       var inputsClosed = false
       val rootNode = WorkflowNode(
@@ -79,12 +76,11 @@ internal object RealWorkflowLoop : WorkflowLoop {
         while (true) {
           coroutineContext.ensureActive()
 
-          val (rendering, debugSnapshot) = rootNode.render(workflow, input)
+          val rendering = rootNode.render(workflow, input)
           val snapshot = rootNode.snapshot(workflow)
 
           onRendering(RenderingAndSnapshot(rendering, snapshot))
-          onDebugSnapshot(WorkflowDebugInfo(debugSnapshot, output?.debugInfo))
-          output?.output?.let { onOutput(it) }
+          output?.let { onOutput(it) }
 
           // Tick _might_ return an output, but if it returns null, it means the state or a child
           // probably changed, so we should re-render/snapshot and emit again.