pipenv 3000 install (behavioral refactor)

[matteius]

The issue

It has been long requested that:
pipenv install have the same behavior as pipenv sync when no packages are requested
and pipenv install package has the behavior of pipenv update
which means only pipenv lock will regenerate the whole lock.

Fixes #5992
Fixes #6070
Fixes #6048

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix.rst, .feature.rst, .behavior.rst, .doc.rst. .vendor.rst. or .trivial.rst (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.

[oz123]

This PR looks good. What's still missing is an update to docs.

[oz123]

We should definitely add documentation about this.

[Kroppeb]

Huh, I'm a bit confused. I only see the logic for pipenv install package having been changed. I don't see where you changed the behavior of pipenv install.

I know some people at my work sometimes edit the pipfile directly and then run pipenv install. Maybe it would be beneficial to see if the lockfile is up to date and if not use the old logic of lock & sync?

[matteius]

Huh, I'm a bit confused. I only see the logic for pipenv install package having been changed.

Thanks for checking, I probably missed something in the refactor -- will revisit soon.