Fix mypy test temporary config file creation

[Avasam]

For a long while now I noticed that when the mypy test fails, No [mypy] section in config file is printed, but I never really paid attention to it. Turns our the temporary mypy config file was never actually being written to.

I also noticed an additional bug where the same config section would be repeated a lot.

I have an upcoming experimental PR that depends on the [mypy-tests] feature, so here you go with some bugfixes and removing a bogus error line that affects current tests.

When there's a mypy error:

Before:

testing setuptools (104 files)... failure (exit code 1)

stubs\setuptools\setuptools\namespaces.pyi:10: error: Name "this_name_doesnt_exist" is not defined  [name-defined]

C:\Users\Avasam\AppData\Local\Temp\tmpe41876qa: No [mypy] section in config file

After:

testing setuptools (104 files)... failure (exit code 1)

stubs\setuptools\setuptools\namespaces.pyi:10: error: Name "this_name_doesnt_exist" is not defined  [name-defined]

On top of the above fix, with the following in METADATA.toml:

[mypy-tests.example]
module_name = "example"
values = { "follow_untyped_imports" = true }

Before (content written to temp file):

[mypy]

[mypy-example]

follow_untyped_imports = True

[mypy-example]

follow_untyped_imports = True

[mypy-example]

follow_untyped_imports = True

[mypy-example]

follow_untyped_imports = True

After (content written to temp file):

[mypy]

[mypy-example]

follow_untyped_imports = True

[Avasam]

According to https://docs.python.org/3/library/tempfile.html#tempfile.NamedTemporaryFile

[...] in case the temporary file is created in a with statement, set the delete_on_close parameter to be false. The latter approach is recommended as it provides assistance in automatic cleaning of the temporary file upon the context manager exit.

[Avasam]

Oh, that's not usable until Python 3.12 . Hopefully delete=False is fine...

I think it should be fine as long as the mypy call closes the file after reading it:

Opening the temporary file again by its name while it is still open works as follows:

• On POSIX the file can always be opened again.
• On Windows, make sure that at least one of the following conditions are fulfilled:

• delete is false

• additional open shares delete access (e.g. by calling os.open() with the flag O_TEMPORARY)

• delete is true but delete_on_close is false. Note, that in this case the additional opens that do not share delete access (e.g. created via builtin open()) must be closed before exiting the context manager, else the os.unlink() call on context manager exit will fail with a PermissionError.

[Akuli]

This will pollute the developer's temp folder with mypy config files.

Are you sure that this change is needed? As far as I can tell, the file is only needed while mypy is running (i.e. we are inside the with block), so there's no need to pass delete=False.

I can't reproduce your No [mypy] section in config file error locally. I added x = asoijfasoif to the end of stubs/setuptools/setuptools/monkey.pyi, and this is what I get:

akuli@akuli-desktop:~/typeshed$ python3 tests/mypy_test.py stubs/setuptools -p 3.13
*** Testing Python 3.13 on linux
Testing third-party packages...
testing setuptools (104 files)... failure (exit code 1)

stubs/setuptools/setuptools/monkey.pyi:17: error: Name "asoijfasoif" is not defined  [name-defined]


--- 1 package with errors, 104 files checked ---

[Avasam]

I think it's a Windows-only issue, I don't get it on WSL either. Likely due to those quirks of tempfile.NamedTemporaryFile mentioned in the documentation.

And yeah that leaves the file behind, maybe I mixed up my tests because I thought I checks for that...

Edit: delete_on_close doesn't leave files behind, it just changes when the deletion happens.

Here's the relevant CPython PR: python/cpython#97015 and original issue: python/cpython#58451

[Akuli]

Maybe try the following:

• Add a manual os.remove() or similar to clean up the file, make sure it works
• Move the os.remove() as close to the end of the with statement as possible
• Figure out why it cannot be simply at the end of the with statement (default behavior of NamedTemporaryFile)

[AlexWaygood]

I remember getting this issue when I used Windows as well FWIW; can confirm that it's not an issue specific to Avasam's environment :-)

[Akuli]

Perhaps we could place a regular file inside the td folder, created in the main() function.

[Avasam]

Well I know why it's a windows issue (after reading the docs): To read the tempfile, you need to first close the tempfile. But the tempfile is immediately deleted on close. Unless you "call os.open() with the flag O_TEMPORARY", but mypy doesn't do that.

So on Pyton >= 3.12, I could just use delete_on_close=False. Before that on Windows specifically I have to pass delete=False and manually delete the file.

[AlexWaygood]

Yeah, I think TemporaryDirectory() has much more reliable cross-platform behaviour than the other tempfile functions

[Avasam]

Ah those comments loaded after I wrote my last answer.

I wrapped NamedTemporaryFile, but it's true there's already a temporary directory that I could try to pass further along. (test_third_party_stubs doesn't pass tempdir to test_third_party_distribution, which is what eventually calls run_mypy)

[sobolevn]

If any contributor runs this on win, it will be a NameError to access _named_temporary_file. I guess we have to explicitly say that win32 platform is not supported for running tests.