Deprecate use of session.install() without a virtual env

[Tolker-KU]

Close #503.

I've scanned the docs and cannot see anything that should be changed based on this change. Please correct me if I'm wrong.

Also feel free to chime in on the wording of the warning message.

[cjolowicz]

I've scanned the docs and cannot see anything that should be changed based on this change. Please correct me if I'm wrong.

I also did not find anything. Should we add a note to config.rst explaining this, though?

It can go into the section introducing venv_backend="none", and can be worded similar to the deprecation warning. Can happen here or in a follow-up PR.

[FollowTheProcess]

Is the intention here to keep this warning for 1 release (presumably the next one?) and then in the following release make it so that doing this will become an actual error? I don't use calver so I don't know if there are any specific rules regarding this.

If so we should probably have a separate issue to track this as I know at least my memory isn't that good!

[cjolowicz]

Is the intention here to keep this warning for 1 release (presumably the next one?) and then in the following release make it so that doing this will become an actual error?

Yes.

I don't use calver so I don't know if there are any specific rules regarding this.

We don't have any specific rules that I know of, but waiting one release should be enough IMO.

If so we should probably have a separate issue to track this as I know at least my memory isn't that good!

Opened #541 for this.

[cjolowicz]

Thanks @Tolker-KU