Check environment variable PIPENV_CUSTOM_VENV_NAME

[otherjake]

Resolves #1226

Allows user to set a custom venv name

The fix

Check for PIPENV_CUSTOM_VENV_NAME environment variable, accept it as venv name at creation if it is set

[oz123]

Instead of asking os.getenv directly, we should go through:

self.s.PIPENV_CUSTOM_VENV_NAME

All settings are found in environments.Settings class.
Using this class conventions is also to document the variable, as other variables are documented there.

[oz123]

Setting PIPENV_CUSTOM_VENV_NAME is going to trick a lot of people if we don't preserve it in Pipefile.

Suppose I did:
export PIPENV_CUSTOM_VENV_NAME=foobar

Now there is:

home/myuser/.virtualenvs/foobar`

If I run pipenv in a new shell it's not going to have PIPENV_CUSTOM_VENV_NAME, hence it will look for an environment
in the hash location, and not in foobar. Hence, I suggest we preserve this in the Pipfile, and read it from there.

@matteius do you have an opinion here?

[matteius]

Setting PIPENV_CUSTOM_VENV_NAME is going to trick a lot of people if we don't preserve it in Pipefile.

@oz123 I am not sure I agree with that approach when its much easier to have a .env file to store the environment variable you want to use for that project -- I fear that if its in the Pipfile it forces everyone on the project to have the same virtualenv name, and some may want the default generated one whereas others want to customize it -- a local .env solves this. Otherwise I might already have a virtualenv setup and my teammate pushes that change to the Pipfile which forces my machine to generate a new virtualenv under this other name.

[otherjake]

I am considering putting self.s.PIPENV_CUSTOM_VENV_NAME into activate in environment.py, that seems like the creating a venv context level that this is appropriate to. Waiting for more consensus around the pipfile bit.

[matteius]

I am considering putting self.s.PIPENV_CUSTOM_VENV_NAME into activate in environment.py

@otherjake The reading of the environment variable should happen in environments.py where the other environment variables are read from.

[oz123]

@matteius true. Putting it in .env is the correct way. Totally forgot we support this.

[oz123]

This obsoletes, #4974. This is a reminder for us to make sure we close that one too.

[matteius]

Nice @otherjake !

[oz123]

@otherjake Thank you for your contribution! I added a small change to your test. Didn't want to bother you again with changes.
Please take a look at it.

Besides that, as usual 💯 points and a big thanks!