(Merge 3.4) Issue #21163, asyncio: Ignore "destroy pending task" warnings for

private tasks in gather().

Lib/asyncio/tasks.py

@@ -558,21 +558,33 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
     prevent the cancellation of one child to cause other children to
     be cancelled.)
     """
-    arg_to_fut = {arg: async(arg, loop=loop) for arg in set(coros_or_futures)}
-    children = [arg_to_fut[arg] for arg in coros_or_futures]
-    n = len(children)
-    if n == 0:
+    if not coros_or_futures:
         outer = futures.Future(loop=loop)
         outer.set_result([])
         return outer
+
+    arg_to_fut = {}
+    for arg in set(coros_or_futures):
+        if not isinstance(arg, futures.Future):
+            fut = async(arg, loop=loop)
             if loop is None:
-        loop = children[0]._loop
-    for fut in children:
-        if fut._loop is not loop:
+                loop = fut._loop
+            # The caller cannot control this future, the "destroy pending task"
+            # warning should not be emitted.
+            fut._log_destroy_pending = False
+        else:
+            fut = arg
+            if loop is None:
+                loop = fut._loop
+            elif fut._loop is not loop:
                 raise ValueError("futures are tied to different event loops")
+        arg_to_fut[arg] = fut
+
+    children = [arg_to_fut[arg] for arg in coros_or_futures]
+    nchildren = len(children)
     outer = _GatheringFuture(children, loop=loop)
     nfinished = 0
-    results = [None] * n
+    results = [None] * nchildren
 
     def _done_callback(i, fut):
         nonlocal nfinished
@@ -595,7 +607,7 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
             res = fut._result
         results[i] = res
         nfinished += 1
-        if nfinished == n:
+        if nfinished == nchildren:
             outer.set_result(results)
 
     for i, fut in enumerate(children):