mypy does not detect pytest-assume

[trym-b]

I am not sure if this is the correct place to file this issue, but the issue I am having with mypy is that it does not detect the functions added by a pytest-plugin.

I created a reproducer script:

mkdir temp_dir
python -m venv temp_dir/virtual-env || exit $?
source temp_dir/virtual-env/bin/activate || exit $?
python -m pip install pytest pytest-assume mypy || exit $?

echo "import pytest
def test_dummy() -> None:
    pytest.assume(1 != 2)
    pytest.assume(3 == 3)" >> "temp_dir/test_dummy_file.py" || exit $?

echo "Mypy version:"
mypy --version || exit $?

echo "Running pytest:"
pytest "temp_dir/test_dummy_file.py" || exit $?

echo "Running mypy:"
mypy "temp_dir/test_dummy_file.py" || exit $?

When run, I get the output:

$ ./pytest-assume.sh 
Collecting pytest
  Using cached pytest-6.0.1-py3-none-any.whl (270 kB)
Collecting pytest-assume
  Using cached pytest_assume-2.3.2-py3-none-any.whl (5.6 kB)
Collecting mypy
  Using cached mypy-0.782-cp38-cp38-manylinux1_x86_64.whl (21.7 MB)
Collecting more-itertools>=4.0.0
  Using cached more_itertools-8.4.0-py3-none-any.whl (43 kB)
Collecting toml
  Using cached toml-0.10.1-py2.py3-none-any.whl (19 kB)
Collecting py>=1.8.2
  Using cached py-1.9.0-py2.py3-none-any.whl (99 kB)
Collecting pluggy<1.0,>=0.12
  Using cached pluggy-0.13.1-py2.py3-none-any.whl (18 kB)
Collecting packaging
  Using cached packaging-20.4-py2.py3-none-any.whl (37 kB)
Collecting iniconfig
  Using cached iniconfig-1.0.1-py3-none-any.whl (4.2 kB)
Collecting attrs>=17.4.0
  Using cached attrs-19.3.0-py2.py3-none-any.whl (39 kB)
Collecting typing-extensions>=3.7.4
  Using cached typing_extensions-3.7.4.2-py3-none-any.whl (22 kB)
Collecting typed-ast<1.5.0,>=1.4.0
  Using cached typed_ast-1.4.1-cp38-cp38-manylinux1_x86_64.whl (768 kB)
Collecting mypy-extensions<0.5.0,>=0.4.3
  Using cached mypy_extensions-0.4.3-py2.py3-none-any.whl (4.5 kB)
Collecting pyparsing>=2.0.2
  Using cached pyparsing-2.4.7-py2.py3-none-any.whl (67 kB)
Collecting six
  Using cached six-1.15.0-py2.py3-none-any.whl (10 kB)
Installing collected packages: more-itertools, toml, py, pluggy, pyparsing, six, packaging, iniconfig, attrs, pytest, pytest-assume, typing-extensions, typed-ast, mypy-extensions, mypy
Successfully installed attrs-19.3.0 iniconfig-1.0.1 more-itertools-8.4.0 mypy-0.782 mypy-extensions-0.4.3 packaging-20.4 pluggy-0.13.1 py-1.9.0 pyparsing-2.4.7 pytest-6.0.1 pytest-assume-2.3.2 six-1.15.0 toml-0.10.1 typed-ast-1.4.1 typing-extensions-3.7.4.2
Mypy version:
mypy 0.782
Running pytest:
================================= test session starts =================================
platform linux -- Python 3.8.2, pytest-6.0.1, py-1.9.0, pluggy-0.13.1
rootdir: /home/trym/testing/bug-mypy
plugins: assume-2.3.2
collected 1 item                                                                      

temp_dir/test_dummy_file.py .                                                   [100%]

================================== 1 passed in 0.02s ==================================
Running mypy:
temp_dir/test_dummy_file.py:3: error: Module has no attribute "assume"
temp_dir/test_dummy_file.py:4: error: Module has no attribute "assume"
Found 2 errors in 1 file (checked 1 source file)

I would expect mypy to be able to find this function, but this is not the case. Is this a quirk of pytest-plugins or is this a bug in mypy?

[gvanrossum]

Is there a typeshed stub for pytest? Does it have a sub-stub for assume? I’m guessing the answers are Yes, No, respectively. Then it would be a typeshed issue.

[trym-b]

I was under the impression that they had enabled type hint in pytest with the latest 6.0.1 release, seen in this issue: pytest-dev/pytest#3342, but this is not the case for pytest-assume.
So the solution is to either add type-hints to the plugin itself, of add a pytest_assume entry in typeshed? If yes, I then I will close this issue.

[gvanrossum]

Since pytest went the way of inline typing and a py.typed marker file, I believe this needs to be added there, not to typeshed.