typing-extensions vs. typing_extensions

[jherland]

While attempting to run FD on itself (after #169), I found this pair in our output:

These imports appear to be undeclared dependencies:
- 'typing_extensions'
These dependencies appear to be unused (i.e. not imported):
- 'typing-extensions'

More checking with --json reveals that we are using the identity mapping for this dependency:

  "unused_deps": [
    {
      "name": "typing-extensions",
      "references": [
        {
          "name": "typing-extensions",
          "source": {
            "path": "pyproject.toml"
          },
          "import_names": [
            "typing-extensions"
          ],
          "mapping": "IDENTITY"
        }
      ]
    }

and the module is indeed not returned from importlib_metadata.packages_distributions(), because we instead get this:

{ 'typing_extensions': ['typing_extensions'], }

meaning that - according to importlib_metadata the package is indeed called typing_extensions. pip also agrees with this:

$ pip list
...
typing_extensions  4.4.0
...

So we have a package that is installed as typing-extensions via our pyproject.toml (and is referred to by this name in many other packages as well, is presented as typing-extensions on PyPI (although searching for either name gets you there), and you can pip install it using either name.

However, no matter how you install it, it will from that point be known as typing_extensions inside your virtualenv.

I wonder if the only way to deal with this is to do the same/similar normalization that most other tools seem to already be doing... 🤔