Be more specific about error messages when `UploadError` is thrown.

• I have searched the issues of this repo and believe that this is not a duplicate.
• I have searched the documentation and believe that my question is not covered.

Feature Request

I have been using poetry for quite a while now. I really appreciate the features that came with it right out the box, from building performance to the sleek modern interface. However, I struggled a bit with publishing my little lovely package to PyPI.

So basically, I used in my readme file the raw directive, later on, I realized that this directive is not allowed on PyPi. But how did I realize that? you may ask. The answer should be, I think, using poetry. Unfortunately, poetry didn't help though.

➜ poetry check
All set!

Trying to publish the dist to PyPi threw the following exception:

➜ poetry publish

Username: harmouch
Password: 
Publishing frozndict (1.0.0) to PyPI
 - Uploading frozndict-1.0.0-py3-none-any.whl 100%

  UploadError

  HTTP Error 400: The description failed to render for 'text/x-rst'. See https://pypi.org/help/#description-content-type for more information.

  at ~/.poetry/lib/poetry/publishing/uploader.py:216 in _upload
      212│                     self._register(session, url)
      213│                 except HTTPError as e:
      214│                     raise UploadError(e)
      215│ 
    → 216│             raise UploadError(e)
      217│ 
      218│     def _do_upload(
      219│         self, session, url, dry_run=False
      220│     ):  # type: (requests.Session, str, Optional[bool]) -> None
make: *** [Makefile:67: release] Error 1

from the error message:

HTTP Error 400: The description failed to render for 'text/x-rst'. See https://pypi.org/help/#description-content-type for more information.

I thought that the issue is related to the description value of my pyproject.toml.

Trying fuzzy values for description didn't help me out.

Then, I thought, well maybe twine can help me figure out the issue. And it did:

➜ twine check dist/*

Checking dist/frozndict-1.0.0-py3-none-any.whl: FAILED
  `long_description` has syntax errors in markup and would not be rendered on PyPI.
    line 5: Warning: "raw" directive disabled.
Checking dist/frozndict-1.0.0.tar.gz: FAILED
  `long_description` has syntax errors in markup and would not be rendered on PyPI.
    line 5: Warning: "raw" directive disabled.

With twine, it is crystal clear that the issue is related to the raw directives being used.

Did some cleanups, and I was successfully able to publish my package to PyPi. 🎉

Takeaway:

• Improvements should be made to the error messages thrown while publishing a package, making it kind of similar to twine.

All in all, poetry rocks.

Start in poetry/publishing/uploader.py around line 216, where the reported UploadError is raised, and compare its output with the twine check messages shown in the issue. Done means publishing reports a more specific explanation of the package description or markup failure instead of only the generic HTTP 400 response.