Better error message for missing RECORD file

[frenzymadness]

What's the problem this feature will solve?
According to PEP 627, the RECORD file is now optional and its absence indicates that a package should not be uninstalled/upgraded by pip or another tool that relies on its content (see the last paragraph in docs). In Fedora, when you install an RPM package without .dist-info/RECORD file and then you try to uninstall it via pip, you'll get a traceback like this:

# pip uninstall django
Found existing installation: Django 3.0.7
ERROR: Exception:
Traceback (most recent call last):
  File "/usr/lib/python3.9/site-packages/pip/_internal/cli/base_command.py", line 216, in _main
    status = self.run(options, args)
  File "/usr/lib/python3.9/site-packages/pip/_internal/commands/uninstall.py", line 89, in run
    uninstall_pathset = req.uninstall(
  File "/usr/lib/python3.9/site-packages/pip/_internal/req/req_install.py", line 685, in uninstall
    uninstalled_pathset = UninstallPathSet.from_dist(dist)
  File "/usr/lib/python3.9/site-packages/pip/_internal/req/req_uninstall.py", line 535, in from_dist
    for path in uninstallation_paths(dist):
  File "/usr/lib/python3.9/site-packages/pip/_internal/req/req_uninstall.py", line 67, in unique
    for item in fn(*args, **kw):
  File "/usr/lib/python3.9/site-packages/pip/_internal/req/req_uninstall.py", line 85, in uninstallation_paths
    r = csv.reader(FakeFile(dist.get_metadata_lines('RECORD')))
  File "/usr/lib/python3.9/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1432, in get_metadata_lines
    return yield_lines(self.get_metadata(name))
  File "/usr/lib/python3.9/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1420, in get_metadata
    value = self._get(path)
  File "/usr/lib/python3.9/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1616, in _get
    with open(path, 'rb') as stream:
FileNotFoundError: [Errno 2] No such file or directory: '/usr/lib/python3.9/site-packages/Django-3.0.7.dist-info/RECORD'

Describe the solution you'd like
It would be nice to produce a better error message for cases like the one described above. It'd be also nice to use .dist-info/INSTALLER file (if exists) to indicate which tool a user should use to work with the package. Note that the INSTALLER file is also optional according to the PEP.

Additional context
PEP 627: https://www.python.org/dev/peps/pep-0627/
Related to: #8156
Packaging docs: https://packaging.python.org/specifications/recording-installed-packages/

Cc: @hroncok

[uranusjr]

Since pkg_resources is a part of setuptools, this should be done in pypa/setuptools first, and pip will upgrade the vendored copy when it drops Python 2 support (in 21.0), or manually apply the patch for 20.3.

[encukou]

Shouldn't refusing to uninstall/upgrade a package with no RECORD be done in pip?
I think pkg_resources.get_metadata_lines is very correct to report FileNotFoundError if the file is not found.

[encukou]

@uranusjr : could you reconsider the "vendored dependency" label? ISTM that pkg_resources.get_metadata_lines is working correctly.

[uranusjr]

You’re right, I misidentified the cause. pip should anticipate the RECORD file may be missing on its own.

[hroncok]

I will work on a PR.

[hroncok]

Here: #9949