I am occasionally seeing Windows tests fail with errors of the form (for various tests):

Traceback (most recent call last):
  File "/c/GitLabRunner/builds/pA2hwqzM/0/SkyWriter/ghc/testsuite/driver/testlib.py", line 973, in test_common_work
    do_test(name, way, func, args, files)
  File "/c/GitLabRunner/builds/pA2hwqzM/0/SkyWriter/ghc/testsuite/driver/testlib.py", line 1071, in do_test
    result = func(*[name,way] + args)
  File "/c/GitLabRunner/builds/pA2hwqzM/0/SkyWriter/ghc/testsuite/driver/testlib.py", line 1199, in compile_fail
    return do_compile( name, way, True, None, [], extra_hc_opts )
  File "/c/GitLabRunner/builds/pA2hwqzM/0/SkyWriter/ghc/testsuite/driver/testlib.py", line 1252, in do_compile
    expected_stderr_file = find_expected_file(name, 'stderr')
  File "/c/GitLabRunner/builds/pA2hwqzM/0/SkyWriter/ghc/testsuite/driver/testlib.py", line 2353, in find_expected_file
    if in_srcdir(f).exists():
  File "/usr/lib/python3.7/pathlib.py", line 1329, in exists
    self.stat()
  File "/usr/lib/python3.7/pathlib.py", line 1151, in stat
    return self._accessor.stat(self)
OSError: [Errno 0] Error: '/c/GitLabRunner/builds/pA2hwqzM/0/SkyWriter/ghc/testsuite/tests/typecheck/should_fail/tcfail161.stderr-mingw32'

Note the Errno 0; this is just bizarre given that tcfail161.sterr-mingw32 doesn't even exist.