tempfile.TemporaryFile(..., dir=dir) does not raise FileNotFoundError on Linux when directory does not exist

[vtsatskin]

Describe the bug
When invoking tempfile.TemporaryFile(..., dir=dir) when dir does not exist on a fake filesystem under Linux, a FileNotFoundError is not raised. This does not occur on macOS.

How To Reproduce

import pytest
from pyfakefs.fake_filesystem import FakeFilesystem
import tempfile

def test_file_not_found(fs: FakeFilesystem) -> None:
    with pytest.raises(FileNotFoundError):
        tempfile.TemporaryFile(dir="/bogus")

This test fails because FileNotFoundError is not raised. When running the test on macOS, it passes.

Checking the expected behaviour using the real filesystem:

# macOS
Python 3.6.7 (v3.6.7:6ec5cf24b7, Oct 20 2018, 03:02:14) 
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import tempfile
>>> tempfile.TemporaryFile(dir="/bogus")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/tempfile.py", line 622, in TemporaryFile
    (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags, output_type)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/tempfile.py", line 262, in _mkstemp_inner
    fd = _os.open(file, flags, 0o600)
FileNotFoundError: [Errno 2] No such file or directory: '/bogus/tmp9fiv_v7v'

# Linux
Python 3.6.9 (default, Nov  7 2019, 10:44:02) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tempfile
>>> tempfile.TemporaryFile(dir="/bogus")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.6/tempfile.py", line 761, in TemporaryFile
    (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags, output_type)
  File "/usr/lib/python3.6/tempfile.py", line 401, in _mkstemp_inner
    fd = _os.open(file, flags, 0o600)
FileNotFoundError: [Errno 2] No such file or directory: '/bogus/tmpnkiv2m_v'

Your enviroment

Linux-4.9.140-tegra-aarch64-with-Ubuntu-18.04-bionic
Python 3.6.9 (default, Nov  7 2019, 10:44:02)
pyfakefs 4.0

[mrbean-bremen]

Thanks - I will probably have a look at this later tomorrow.

[mrbean-bremen]

Ok, please check with master - hopefully this fixes the problem. It was caused by the same linux-specific O_TMPFILE flag as the previous one.