extmod/uasyncio: Fix gather cancelling and handling of exceptions.

The following fixes are made:
- cancelling a gather now cancels all sub-tasks of the gather (previously
  it would only cancel the first)
- if any sub-task of a gather raises an exception then the gather finishes
  (previously it would only finish if the first sub-task raised)

Fixes issues #5798, #7807, #7901.

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 53 insertions, 0 deletions

diff --git a/tests/extmod/uasyncio_gather_notimpl.py b/tests/extmod/uasyncio_gather_notimpl.py
new file mode 100644
index 0000000000..3ebab9bad6
--- /dev/null
+++ b/tests/extmod/uasyncio_gather_notimpl.py
@@ -0,0 +1,53 @@
+# Test uasyncio.gather() function, features that are not implemented.
+
+try:
+    import uasyncio as asyncio
+except ImportError:
+    try:
+        import asyncio
+    except ImportError:
+        print("SKIP")
+        raise SystemExit
+
+
+def custom_handler(loop, context):
+    print(repr(context["exception"]))
+
+
+async def task(id):
+    print("task start", id)
+    await asyncio.sleep(0.01)
+    print("task end", id)
+    return id
+
+
+async def gather_task(t0, t1):
+    print("gather_task start")
+    await asyncio.gather(t0, t1)
+    print("gather_task end")
+
+
+async def main():
+    loop = asyncio.get_event_loop()
+    loop.set_exception_handler(custom_handler)
+
+    # Test case where can't wait on a task being gathered.
+    tasks = [asyncio.create_task(task(1)), asyncio.create_task(task(2))]
+    gt = asyncio.create_task(gather_task(tasks[0], tasks[1]))
+    await asyncio.sleep(0)  # let the gather start
+    try:
+        await tasks[0]  # can't await because this task is part of the gather
+    except RuntimeError as er:
+        print(repr(er))
+    await gt
+
+    print("====")
+
+    # Test case where can't gather on a task being waited.
+    tasks = [asyncio.create_task(task(1)), asyncio.create_task(task(2))]
+    asyncio.create_task(gather_task(tasks[0], tasks[1]))
+    await tasks[0]  # wait on this task before the gather starts
+    await tasks[1]
+
+
+asyncio.run(main())