Improved error message from: [directory] is not a valid Python package name

[doctrino]

Bug Report

Executing mypy fails with some strange error message.

To Reproduce

>>> mypy run cognite/neat
source-graphs is not a valid Python package name

In the root of the public repo: https://github.com/cognitedata/neat

Same for dmypy

>>> dmypy run -- cognite/neat
source-graphs is not a valid Python package name

Expected Behavior

Execute validation of the files in the package.

Actual Behavior

It responds: source-graphs is not a valid Python package name

Digging into the source code of mypy it seems to be hitting here
https://github.com/python/mypy/blob/master/mypy/find_sources.py#L187

Your Environment

• Mypy version used: 1.9
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):

[tool.mypy]
explicit_package_bases = true
allow_redefinition = true
plugins = ["pydantic.mypy"]

• Python version used: 3.12
• OS: Windows

If I specify a different path MyPy works as normal, for example,

mypy run cognite/neat/rules

[doctrino]

I have done some more digging an found the issue.

I have a folder structure such as this:

📦Repo Root
 ┗ 📂cognite- The package I want to run mypy on.
    ....
      ┗  📂data- folder deep inside the package
            ┗  📂source-graphs
                  ┣ 📜__init__.py
                        ....
                  ┗ 📜some other files

So this is a user fault, however, it would be helpful with a more informative error message as I did not know about this error inside the package.

[doctrino]

Note I would no longer label this as a bug :) Sorry for the inconvenience of mislabeling this issue.