Support custom session names in --keywords expression

[nawatts]

How would this feature be useful?

Currently, providing a --keywords argument that is not a valid expression causes Nox to crash with a SyntaxError.

$ nox -k 'foo:bar'
Traceback (most recent call last):
  ...
  File "<string>", line 1
    foo:bar
       ^
SyntaxError: invalid syntax

The value of the --keywords argument should be a Python expression. That expression is evaluated to filter the list of sessions.

/~https://github.com/theacodes/nox/blob/a2bd140ed9702428d3fc93be9857879388f21ad0/nox/manifest.py#L347-L350

However, I don't think that's entirely obvious. The name of the argument is --keywords and the docs also refer to "pytest-style keywords".

The issue arises if the user attempts to do a keyword match on a custom session name, which may contain characters that are not valid in Python identifiers. Using one of those characters in the --keywords expression raises a SyntaxError when it is evaluated.

Nox could provide some guidance here on how to resolve the issue. With the current behavior (printing a SyntaxError and stack trace), it's not clear to the user whether the issue is an invalid argument or a bug in Nox.

Describe the solution you'd like

It would be nice if the keywords argument could support matching on session names, including characters that aren't allowed in Python identifiers.

Describe alternatives you've considered

Validating the keywords expression and printing a descriptive error message (#493) would help users resolve the error.

[FollowTheProcess]

Closing due to fix in #493 Thanks 🎉

[FollowTheProcess]

Sorry didn't fully read! Issue refers to a slightly different feature than the fix in #493. My bad!

[nawatts]

Sorry, I did kind of conflate two separate, though related, issues here.