Error when running on code inside venv containing `typing-extensions`

Bug Report

When running mypy on code installed in a virtualenv environment, mypy will fail outright if the environment contains typing-extensions.

To Reproduce

See repo containing a minimal example. The steps below describe the general idea:

1. Create a fresh virtual environment.
2. Create a minimal library with a setup.py that lists typing-extensions in install_requires.
3. Install the library to the virtual environment.
4. Run mypy on a file inside the environment that is part of the library (mypy venv/lib/python3.Y/site-packages/my_project/hello.py).

Expected Behavior

mypy would report errors in hello.py, if any, or exit with 0 if none.

Actual Behavior

mypy doesn't check hello.py, complaining that it found a typing_extensions.py in the environment:

mypy: "project-venv/lib/python3.6/site-packages/typing_extensions.py" shadows library module "typing_extensions"
note: A user-defined top-level module with name "typing_extensions" is not supported

Your Environment

• Mypy version used: 0.910.
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: multiple (3.6.8, 3.8.8).
• Operating system and version: CentOS 7

Commencez par l’exemple minimal du dépôt mypy-typing-extensions-issue lié et reproduisez la commande avec un paquet installé dans un environnement virtuel. Suivez le point d’entrée de résolution des modules de mypy pour l’erreur de shadowing signalée, puis vérifiez que la hello.py cible est vérifiée comme prévu sans cette erreur.