From 52cc925e0e34580403b1a405ec8b4fa44c844de5 Mon Sep 17 00:00:00 2001
From: Dominik Picheta <dominikpicheta@gmail.com>
Date: Fri, 22 Dec 2017 21:14:27 +0000
Subject: [PATCH] Fixes #6100.

---
 lib/pure/asyncfutures.nim     |  6 +++---
 lib/pure/asyncmacro.nim       |  6 ++++++
 tests/async/t6100.nim         | 15 +++++++++++++++
 tests/async/tfuturestream.nim |  2 +-
 4 files changed, 25 insertions(+), 4 deletions(-)
 create mode 100644 tests/async/t6100.nim

diff --git a/lib/pure/asyncfutures.nim b/lib/pure/asyncfutures.nim
index 4bd3227a11..69db4d7125 100644
--- a/lib/pure/asyncfutures.nim
+++ b/lib/pure/asyncfutures.nim
@@ -263,12 +263,12 @@ proc mget*[T](future: FutureVar[T]): var T =
   ## Future has not been finished.
   result = Future[T](future).value
 
-proc finished*[T](future: Future[T] | FutureVar[T]): bool =
+proc finished*(future: FutureBase | FutureVar): bool =
   ## Determines whether ``future`` has completed.
   ##
   ## ``True`` may indicate an error or a value. Use ``failed`` to distinguish.
-  when future is FutureVar[T]:
-    result = (Future[T](future)).finished
+  when future is FutureVar:
+    result = (FutureBase(future)).finished
   else:
     result = future.finished
 
diff --git a/lib/pure/asyncmacro.nim b/lib/pure/asyncmacro.nim
index a8e378d5c4..35523702d4 100644
--- a/lib/pure/asyncmacro.nim
+++ b/lib/pure/asyncmacro.nim
@@ -32,6 +32,12 @@ template createCb(retFutureSym, iteratorNameSym,
     try:
       if not nameIterVar.finished:
         var next = nameIterVar()
+        # Continue while the yielded future is already finished.
+        while (not next.isNil) and next.finished:
+          next = nameIterVar()
+          if nameIterVar.finished:
+            break
+
         if next == nil:
           if not retFutureSym.finished:
             let msg = "Async procedure ($1) yielded `nil`, are you await'ing a " &
diff --git a/tests/async/t6100.nim b/tests/async/t6100.nim
new file mode 100644
index 0000000000..b4dc0f1469
--- /dev/null
+++ b/tests/async/t6100.nim
@@ -0,0 +1,15 @@
+discard """
+  file: "t6100.nim"
+  exitcode: 0
+  output: "10000000"
+"""
+import asyncdispatch
+
+let done = newFuture[int]()
+done.complete(1)
+
+proc asyncSum: Future[int] {.async.} =
+  for _ in 1..10_000_000:
+    result += await done
+
+echo waitFor asyncSum()
\ No newline at end of file
diff --git a/tests/async/tfuturestream.nim b/tests/async/tfuturestream.nim
index 9a8e986a09..d76752b7ea 100644
--- a/tests/async/tfuturestream.nim
+++ b/tests/async/tfuturestream.nim
@@ -18,8 +18,8 @@ var fs = newFutureStream[int]()
 
 proc alpha() {.async.} =
   for i in 0 .. 5:
-    await sleepAsync(1000)
     await fs.write(i)
+    await sleepAsync(1000)
 
   echo("Done")
   fs.complete()