Introduction of erroneous newlines in Requires-Dist

[pelson]

Thanks for this project! Was suggested to me in pypa/setuptools#4220 (reply in thread). I noticed that adding a Requires-External modified other parts of the metadata in an incorrect way...

With the normal setuptools backend, I have a record such as the following in METADATA:

Requires-Dist: typing-extensions <5,>=4.2 ; (python_version < "3.8") and extra == 'all'

Meanwhile, with the setuptools-ext backend enabled, you get:

Requires-Dist: typing-extensions <5,>=4.2 ;
 (python_version < "3.8") and extra == 'all'

This is not a valid specification, and results in a unusable wheel. It looks like this comes from email, where https://docs.python.org/3/library/email.generator.html#email.generator.BytesGenerator has a maxlinelength parameter. The value comes from the policy (that is not specified) that you get when you call email.message_from_string - the limit is 78 chars https://docs.python.org/3/library/email.policy.html#email.policy.Policy.max_line_length.

[wimglenn]

@pelson Thanks for the report. Fixed in 0.6.

[pelson]

Nice. Tested and it works great! Thanks for the project! 👍