Fix #470: Prevent error `AsyncToSync.main_wrap() got multiple values …

…for argument '<kwarg>'` (#471)

Replace partial with pre-created awaitable to ensure kwargs/args can't be stepped on

asgiref/sync.py

@@ -217,8 +217,12 @@ def __call__(self, *args: _P.args, **kwargs: _P.kwargs) -> _R:
                 sys.exc_info(),
                 task_context,
                 context,
-                *args,
-                **kwargs,
+                # prepare an awaitable which can be passed as is to self.main_wrap,
+                # so that `args` and `kwargs` don't need to be
+                # destructured when passed to self.main_wrap
+                # (which is required by `ParamSpec`)
+                # as that may cause overlapping arguments
+                self.awaitable(*args, **kwargs),
             )
 
             if not (self.main_event_loop and self.main_event_loop.is_running()):
@@ -302,8 +306,7 @@ async def main_wrap(
         exc_info: "OptExcInfo",
         task_context: "Optional[List[asyncio.Task[Any]]]",
         context: List[contextvars.Context],
-        *args: _P.args,
-        **kwargs: _P.kwargs,
+        awaitable: Union[Coroutine[Any, Any, _R], Awaitable[_R]],
     ) -> None:
         """
         Wraps the awaitable with something that puts the result into the
@@ -326,9 +329,9 @@ async def main_wrap(
                 try:
                     raise exc_info[1]
                 except BaseException:
-                    result = await self.awaitable(*args, **kwargs)
+                    result = await awaitable
             else:
-                result = await self.awaitable(*args, **kwargs)
+                result = await awaitable
         except BaseException as e:
             call_result.set_exception(e)
         else:

tests/test_sync.py

@@ -7,6 +7,7 @@
 import warnings
 from concurrent.futures import ThreadPoolExecutor
 from functools import wraps
+from typing import Any
 from unittest import TestCase
 
 import pytest
@@ -1174,3 +1175,36 @@ async def async_task():
         assert task_complete
 
     assert task_executed
+
+
+def test_async_to_sync_overlapping_kwargs() -> None:
+    """
+    Tests that AsyncToSync correctly passes through kwargs to the wrapped function,
+    particularly in the case where the wrapped function uses same names for the parameters
+    as the wrapper.
+    """
+
+    @async_to_sync
+    async def test_function(**kwargs: Any) -> None:
+        assert kwargs
+
+    # AsyncToSync.main_wrap has a param named `context`.
+    # So we pass the same argument here to test for the error
+    # "AsyncToSync.main_wrap() got multiple values for argument '<kwarg>'"
+    test_function(context=1)
+
+
+@pytest.mark.asyncio
+async def test_sync_to_async_overlapping_kwargs() -> None:
+    """
+    Tests that SyncToAsync correctly passes through kwargs to the wrapped function,
+    particularly in the case where the wrapped function uses same names for the parameters
+    as the wrapper.
+    """
+
+    @sync_to_async
+    def test_function(**kwargs: Any) -> None:
+        assert kwargs
+
+    # SyncToAsync.__call__.loop.run_in_executor has a param named `task_context`.
+    await test_function(task_context=1)