Missing metadata from some sdists

[Tres Seaver]

Via e-mail, wim (wim.glenn@<elided>.com) reported:

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I don't seem to be able to get metadata correctly for
sdist sometimes, is that expected or a bug?
Here is an example where pkginfo can not get the correct metadata from the latest requests (2.19.1) sdist, but it can get it from the bdist_wheel ok.

$ pip install --upgrade pkginfo
Collecting pkginfo
  Using cached
https://files.pythonhosted.org/packages/a3/fe/f32a48d48f40a7209be9825fba2566cab92364787cf37de2e08300dd6ce7/pkginfo-1.4.2-py2.py3-none-any.whl
Installing collected packages: pkginfo
Successfully installed pkginfo-1.4.2
$ pip download --no-deps requests
Collecting requests
  Using cached
https://files.pythonhosted.org/packages/65/47/7e02164a2a3db50ed6d8a6ab1d6d60b69c4c3fdf57a284257925dfc12bda/requests-2.19.1-py2.py3-none-any.whl
  Saved ./requests-2.19.1-py2.py3-none-any.whl
Successfully downloaded requests
$ pip download --no-deps --no-binary :all: requests
Collecting requests
  Using cached
https://files.pythonhosted.org/packages/54/1f/782a5734931ddf2e1494e4cd615a51ff98e1879cbe9eecbdfeaf09aa75e9/requests-2.19.1.tar.gz
  Saved ./requests-2.19.1.tar.gz
Successfully downloaded requests
$ python3
Python 3.7.0 (default, Jun 29 2018, 20:13:13)
[Clang 9.1.0 (clang-902.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from pkginfo import get_metadata
>>> get_metadata('./requests-2.19.1-py2.py3-none-any.whl').requires_dist
['chardet (<3.1.0,>=3.0.2)', 'idna (<2.8,>=2.5)', 'urllib3
(<1.24,>=1.21.1)', 'certifi (>=2017.4.17)', "pyOpenSSL (>=0.14); extra ==
'security'", "cryptography (>=1.3.4); extra == 'security'", "idna
(>=2.0.0); extra == 'security'", "PySocks (!=1.5.7,>=1.5.6); extra ==
'socks'", 'win-inet-pton; sys_platform == "win32" and (python_version ==
"2.7" or python_version == "2.6") and extra == \'socks\'']
>>>
>>> get_metadata('./requests-2.19.1.tar.gz').requires_dist
()

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[Tres Seaver (tseaver)]

Hmm, looking at the 'requests-2.19.1' wheel vs the sdist: the wheel contains a 'METADATA' file with the expected 'Requires-Dist' headers, generated from the 'install_requires' in the sdist's 'setup.py'. However, the sdist's 'PKG-INFO' file does *not* contain those headers. There isn't much we can do in 'pkginfo' to fix that.