IEnumerator.ToUniTask() behave same as StartCoroutine #120

src/UniTask/Assets/Plugins/UniTask/Runtime/EnumeratorAsyncExtensions.cs

@@ -44,6 +44,7 @@ namespace Cysharp.Threading.Tasks
 
             IEnumerator innerEnumerator;
             CancellationToken cancellationToken;
+            int initialFrame;
 
             UniTaskCompletionSourceCore<object> core;
 
@@ -66,10 +67,13 @@ namespace Cysharp.Threading.Tasks
 
                 result.innerEnumerator = ConsumeEnumerator(innerEnumerator);
                 result.cancellationToken = cancellationToken;
+                result.initialFrame = -1;
 
                 PlayerLoopHelper.AddAction(timing, result);
 
                 token = result.core.Version;
+
+                result.MoveNext(); // run immediately.
                 return result;
             }
 
@@ -108,6 +112,19 @@ namespace Cysharp.Threading.Tasks
                     return false;
                 }
 
+                if (initialFrame == -1)
+                {
+                    // Time can not touch in threadpool.
+                    if (PlayerLoopHelper.IsMainThread)
+                    {
+                        initialFrame = Time.frameCount;
+                    }
+                }
+                else if (initialFrame == Time.frameCount)
+                {
+                    return true; // already executed in first frame, skip.
+                }
+
                 try
                 {
                     if (innerEnumerator.MoveNext())

src/UniTask/Assets/Tests/CoroutineToUniTaskTest.cs

@@ -0,0 +1,126 @@
+#if CSHARP_7_OR_LATER || (UNITY_2018_3_OR_NEWER && (NET_STANDARD_2_0 || NET_4_6))
+#pragma warning disable CS1591 // Missing XML comment for publicly visible type or member
+
+using UnityEngine;
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using UnityEngine.UI;
+using UnityEngine.Scripting;
+using Cysharp.Threading.Tasks;
+using Unity.Collections;
+using System.Threading;
+using NUnit.Framework;
+using UnityEngine.TestTools;
+using FluentAssertions;
+
+namespace Cysharp.Threading.TasksTests
+{
+    public class CoroutineToUniTaskTest
+    {
+        [UnityTest]
+        public IEnumerator EarlyUpdate() => UniTask.ToCoroutine(async () =>
+        {
+            await UniTask.Yield(PlayerLoopTiming.EarlyUpdate);
+
+            var l = new List<(int, int)>();
+            var currentFrame = Time.frameCount;
+            var t = Worker(l).ToUniTask();
+
+            l.Count.Should().Be(1);
+            l[0].Should().Be((0, currentFrame));
+
+            await t;
+
+            l[1].Should().Be((1, Time.frameCount));
+            l[1].Item2.Should().NotBe(currentFrame);
+        });
+
+        [UnityTest]
+        public IEnumerator LateUpdate() => UniTask.ToCoroutine(async () =>
+        {
+            await UniTask.Yield(PlayerLoopTiming.PostLateUpdate);
+
+            var l = new List<(int, int)>();
+            var currentFrame = Time.frameCount;
+            var t = Worker(l).ToUniTask();
+
+            l.Count.Should().Be(1);
+            l[0].Should().Be((0, currentFrame));
+
+            await t;
+
+            l[1].Should().Be((1, Time.frameCount));
+            l[1].Item2.Should().NotBe(currentFrame);
+        });
+
+        //[UnityTest]
+        //public IEnumerator TestCoroutine()
+        //{
+        //    yield return UniTask.Yield(PlayerLoopTiming.EarlyUpdate).ToUniTask().ToCoroutine();
+
+        //    var nanika = (UnityEngine.MonoBehaviour)GameObject.FindObjectOfType(typeof(UnityEngine.MonoBehaviour));
+
+        //    var l = new List<(int, int)>();
+        //    var currentFrame = Time.frameCount;
+        //    var t = nanika.StartCoroutine(Worker(l));
+
+        //    l.Count.Should().Be(1);
+        //    l[0].Should().Be((0, currentFrame));
+
+        //    yield return t;
+
+        //    l[1].Should().Be((1, Time.frameCount));
+        //    l[1].Item2.Should().NotBe(currentFrame);
+        //}
+
+        //[UnityTest]
+        //public IEnumerator TestCoroutine2()
+        //{
+        //    yield return UniTask.Yield(PlayerLoopTiming.PostLateUpdate).ToUniTask().ToCoroutine();
+
+        //    var nanika = (UnityEngine.MonoBehaviour)GameObject.FindObjectOfType(typeof(UnityEngine.MonoBehaviour));
+
+        //    var l = new List<(int, int)>();
+        //    var currentFrame = Time.frameCount;
+        //    var t = nanika.StartCoroutine(Worker(l));
+
+        //    l.Count.Should().Be(1);
+        //    l[0].Should().Be((0, currentFrame));
+
+        //    yield return t;
+
+        //    l[1].Should().Be((1, Time.frameCount));
+        //    l[1].Item2.Should().NotBe(currentFrame);
+        //}
+
+        IEnumerator Worker(List<(int, int)> l)
+        {
+            l.Add((0, Time.frameCount));
+            yield return null;
+            l.Add((1, Time.frameCount));
+        }
+
+        public async UniTask Foo()
+        {
+            var tasks = new List<UniTask>();
+            var t = Bar<int>();
+            tasks.Add(t);
+
+            t = Bar<int>();
+            tasks.Add(t);
+
+            await UniTask.WhenAll(tasks);
+        }
+
+        public async UniTask<T> Bar<T>()
+        {
+            await UniTask.Yield();
+            return default(T);
+        }
+    }
+}
+
+#endif

src/UniTask/Assets/Tests/CoroutineToUniTaskTest.cs.meta

@@ -0,0 +1,11 @@
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