From 85328f5d5b94349902238935dff6436174039aaf Mon Sep 17 00:00:00 2001
From: Zach Klippenstein <zachklipp@squareup.com>
Date: Sun, 28 Jun 2020 13:36:07 -0700
Subject: [PATCH 1/2] Add a passing test for the ordering of rendering and
 output emissions.

---
 .../squareup/workflow/RenderWorkflowInTest.kt | 35 +++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/workflow-runtime/src/test/java/com/squareup/workflow/RenderWorkflowInTest.kt b/workflow-runtime/src/test/java/com/squareup/workflow/RenderWorkflowInTest.kt
index 1c402b498a..89c3bfda8f 100644
--- a/workflow-runtime/src/test/java/com/squareup/workflow/RenderWorkflowInTest.kt
+++ b/workflow-runtime/src/test/java/com/squareup/workflow/RenderWorkflowInTest.kt
@@ -26,6 +26,8 @@ import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.consumeAsFlow
+import kotlinx.coroutines.flow.launchIn
+import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.isActive
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.suspendCancellableCoroutine
@@ -363,5 +365,38 @@ class RenderWorkflowInTest {
     assertFalse(scope.isActive)
   }
 
+  @Test fun `output is emitted before next render pass`() {
+    val outputTrigger = CompletableDeferred<String>()
+    // A workflow whose state and rendering is the last output that it emitted.
+    val workflow = Workflow.stateful<Unit, String, String, String>(
+        initialState = { "{no output}" },
+        render = { _, state ->
+          runningWorker(Worker.from { outputTrigger.await() }) { output ->
+            action {
+              setOutput(output)
+              nextState = output
+            }
+          }
+          return@stateful state
+        }
+    )
+    val scope = TestCoroutineScope()
+    val events = mutableListOf<String>()
+    renderWorkflowIn(workflow, scope, MutableStateFlow(Unit)) { events += "output($it)" }
+        .onEach { events += "rendering(${it.rendering})" }
+        .launchIn(scope)
+    assertEquals(listOf("rendering({no output})"), events)
+
+    outputTrigger.complete("output")
+    assertEquals(
+        listOf(
+            "rendering({no output})",
+            "rendering(output)",
+            "output(output)"
+        ),
+        events
+    )
+  }
+
   private class ExpectedException : RuntimeException()
 }

From b084b16cf72618702e442e8ceac99cf168debbcd Mon Sep 17 00:00:00 2001
From: Zach Klippenstein <zachklipp@squareup.com>
Date: Sun, 28 Jun 2020 09:12:59 -0700
Subject: [PATCH 2/2] Emit output before next render pass.

Fixes #54.
---
 .../src/main/java/com/squareup/workflow/RenderWorkflow.kt   | 6 ++----
 .../test/java/com/squareup/workflow/RenderWorkflowInTest.kt | 4 ++--
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/workflow-runtime/src/main/java/com/squareup/workflow/RenderWorkflow.kt b/workflow-runtime/src/main/java/com/squareup/workflow/RenderWorkflow.kt
index 98425aef84..179dae4c51 100644
--- a/workflow-runtime/src/main/java/com/squareup/workflow/RenderWorkflow.kt
+++ b/workflow-runtime/src/main/java/com/squareup/workflow/RenderWorkflow.kt
@@ -158,12 +158,10 @@ fun <PropsT, OutputT, RenderingT> renderWorkflowIn(
         // It might look weird to start by consuming the output before getting the rendering below,
         // but remember the first render pass already occurred above, before this coroutine was even
         // launched.
-        val output = runner.nextOutput()
+        runner.nextOutput()
+            ?.let { onOutput(it.value) }
 
-        // After receiving an output, the next render pass must be done before emitting that output,
-        // so that the workflow states appear consistent to observers of the outputs and renderings.
         renderingsAndSnapshots.value = runner.nextRendering()
-        output?.let { onOutput(it.value) }
       }
   }
 
diff --git a/workflow-runtime/src/test/java/com/squareup/workflow/RenderWorkflowInTest.kt b/workflow-runtime/src/test/java/com/squareup/workflow/RenderWorkflowInTest.kt
index 89c3bfda8f..cb06bdd98d 100644
--- a/workflow-runtime/src/test/java/com/squareup/workflow/RenderWorkflowInTest.kt
+++ b/workflow-runtime/src/test/java/com/squareup/workflow/RenderWorkflowInTest.kt
@@ -391,8 +391,8 @@ class RenderWorkflowInTest {
     assertEquals(
         listOf(
             "rendering({no output})",
-            "rendering(output)",
-            "output(output)"
+            "output(output)",
+            "rendering(output)"
         ),
         events
     )