new 'pre' syntax in Pipfile

Placeholder ticket for the proposition we talk with Kenneth.

Add the following syntax in the Pipfile:

...
mypkg = { version = "*", pre="true"}
...

This would allow to allow prerelease resolution for one package only.

Change the pipenv install mypkg --pre behavior. It will set the setting described above only for this very package. Today it turns on a general ‘pre’ setting for the whole Pipfile, leading other packages to also resolve to prerelease.

Change the pipenv update and pipenv lock behavior. They should take into account the presence of the pre=true setting for some package.

Here are some impact I think might happen

• if a version of package is describe at >=1.0 in one dependency, and another package define the pre=true while a new version 2.0.0.b1 is available on pypi, pipenv install should take it
• I don’t see any syntax to turn the general pre setting in the Pipfile. Maybe we can document users need to do a pipenv update --pre or pipenv lock --pre to turn the general ‘pre’ settings on.

[ncoghlan]

Just noting that pipenv isn’t currently abiding by one of the usability recommendations that was included in the PEP 440 specification. Specifically: “By default, dependency resolutions tools SHOULD … accept remotely available pre-releases for version specifiers where there is no final or post release that satisfies the version specifier”

[andrey-semakin]

It constantly bits me, because black doesn’t have stable releases yet.

pipenv + black = 💥