Add ability for many nox tasks to reuse the same session/virtual env

[DDaxler]

How would this feature be useful?
On windows its slow to build a new environment, having to build identical environments seems a waste.

Describe the solution you'd like

import nox

@nox.session(python="3.6")
def all_tests(session):
    session.install('-rrequirements.txt')
    session.install('-rrequirements_test.txt')
    session.install('-rrequirements_docs.txt')
    session.install('-rrequirements_dist.txt')

@nox.session(reuse="all_tests")
def build_docs(session):
    session.run('sphinx-build', 'source', 'build/html')

@nox.session(reuse="all_tests")
def pylint(session):
    session.run("pylint", "code")

@nox.session(reuse="all_tests")
def yapf(session):
    session.run("yapf", "-r", "-d", "code")

reuse is the new "function"

Describe alternatives you've considered
Havent found an easy way to reuse environments.

[stsewd]

I think a way of doing this would be using https://nox.readthedocs.io/en/stable/config.html#nox.sessions.Session.posargs, of course you'll lose the feature of listing sessions (nox -l)

Also, maybe #72 is more useful here?

[stsewd]

Maybe doing this from the command line? Like nox -s lint tests --share-env.

[paunovic]

Are there plans to implement this? I'd be happy to work on it and create a feature PR.

[theacodes]

Go for it! Let us know if you need help.

…

On Fri, Jan 10, 2020, 6:37 PM Marko Paunovic ***@***.***> wrote: Are there plans to implement this? I'd be happy to work on this and create a PR. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#167>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAB5I43APPEA33IG5BFJNLDQ5EBCDANCNFSM4GYEQ5TA> .

[cs01]

A related approach that would save time around environment creation/reuse is #265.

[theacodes]

I like the solution proposed at #286 (comment)

[Spectre5]

I also like the solution proposed at #286 (comment). Just a quick thought, you can use "notify" to simulate some parts of this, with some caveats:

• Only one session can run on any Nox invocation, as you can't use that shared environment more than once.
• This doesn't attempt to handle the "requires", which would certainly be nice to have at times.

import nox

nox.options.reuse_existing_virtualenvs = True

@nox.session
def shared_venv(session):
    session.install('black')
    session.install('isort')
    session.install('flake8')

    if session.posargs and session.posargs[0] == 'format':
        session.run('black', '.')
        session.run('isort', '.')
    elif session.posargs and session.posargs[0] == 'lint':
        session.run('black', '--check', '.')
        session.run('isort', '--check-only', '.')
        session.run('flake8')

@nox.session
def format(session):
    session.notify('shared_venv', posargs=['format'])

@nox.session
def lint(session):
    session.notify('shared_venv', posargs=['lint'])

This could then be used as below. The first invocation will only create that shared virtual environment since the other two only notify that one, which will be ignored since each session can only run once. The second two only "lint" or only "format" the code. But only one could be done on each invocation of Nox.

$ nox
$ nox -s lint
$ nox -s format

This obviously isn't a very great solution, but just something that came to mind. I'd certainly like to get the proper solution implemented.

[gschaffner]

Hi all! There is an implementation of this over on #631 (comment). It would be great to get some feedback there.

[henryiii]

FYI, this was the syntax I came up with thinking about this before reading the issues:

import nox

@nox.env(python="3.6")
def all_tests(session):
    session.install('-rrequirements.txt')
    session.install('-rrequirements_test.txt')
    session.install('-rrequirements_docs.txt')
    session.install('-rrequirements_dist.txt')

@all_tests.session()
def build_docs(session):
    session.run('sphinx-build', 'source', 'build/html')

@all_tests.session()
def pylint(session):
    session.run("pylint", "code")

@all_tests.session()
def yapf(session):
    session.run("yapf", "-r", "-d", "code")

You could even pass a restricted session in this case that wouldn't allow install in the sessions to reduce potential for order dependent behavior. I assume this is quite a bit of work, just putting down what I though of.