pythongh-104340: Suppress warning about unawaited exception for closed pipe stdin (python#104586)

Author: gvanrossum

Lib/asyncio/subprocess.py

@@ -81,6 +81,9 @@ def pipe_connection_lost(self, fd, exc):
                 self._stdin_closed.set_result(None)
             else:
                 self._stdin_closed.set_exception(exc)
+                # Since calling `wait_closed()` is not mandatory,
+                # we shouldn't log the traceback if this is not awaited.
+                self._stdin_closed._log_traceback = False
             return
         if fd == 1:
             reader = self.stdout

Misc/NEWS.d/next/Library/2023-05-17-20-03-01.gh-issue-104340.kp_XmX.rst

@@ -0,0 +1 @@
+When an ``asyncio`` pipe protocol loses its connection due to an error, and the caller doesn't await ``wait_closed()`` on the corresponding ``StreamWriter``, don't log a warning about an exception that was never retrieved. After all, according to the ``StreamWriter.close()`` docs, the ``wait_closed()`` call is optional ("not mandatory").