Add "color" install extra

[GergelyKalmar]

Allowing the user to install color support through an install extra (e.g. pip install pytest[color]) would be nicer than requiring that a random package be placed in the long list of requirements, I think.

It should be quite straightforward to implement this (see https://setuptools.readthedocs.io/en/latest/setuptools.html#declaring-extras-optional-features-with-their-own-dependencies).

[GergelyKalmar]

Related to #7132 as well.

[asottile]

iirc the plan of record is to make pygments a normal dependency of pytest, the syntax coloring right now is considered experimental

[nicoddemus]

@asottile is correct: it is experimental at the moment and we're not 100% sure we will go with pygments just yet, that's why also there's no option to configure styles.

Because it is uncertain, I would not like to add an extra just now because extras can be considered part of the public API.

[GergelyKalmar]

With pytest 7 out it seems that Pygments-based coloring is now less of an experimental feature – would it perhaps make sense to consider adding it to the list of regular requirements (or as an extra if the opt-in route is preferred)?

[nicoddemus]

It has been some years now and I we don't have plans to move away from pygments any time soon.

I think the safest approach is to add it as an extra dependency (color?). I would avoid making it a normal dependency for now, because pygments itself uses pytest.

It would be great if anyone could contribute a PR with that. 👍

[The-Compiler]

I would avoid making it a normal dependency for now, because pygments itself uses pytest.

Is that really as much as a problem as it used to be in previous years, and if so, can we do something about that?

For what it's worth, we already are in the same situation for exceptiongroup, packaging and (maybe to a lesser extent, as under our control) iniconfig and pluggy. We also were in the same situation with attrs, and from what I can see in #10669 this never was an argument (at least when removing it).

[The-Compiler]

Oh, and as for why it IMHO shouldn't be an optional dependency:

• Just more moving parts. Our testsuite breaks without pygments installed, so if we accidentally do a change that makes Pygments non-optional, we would never notice.
• Way less discoverability. Even if documented, most people will just pip install pytest and not know they're missing out on nicer output.
• Convenience. I test a lot of things in throw-away virtualenvs (also for reproducing pytest bugs and whatnot), and I usually don't think about also installing pygments even if I know that pytest would use it if present.

[nicoddemus]

Thanks @The-Compiler, good points about this already being a problem for exceptiongroup and packaging, I guess this is not much of a problem in practice then.

That said then I'm OK with just adding pygments as a normal dependency.

[The-Compiler]

Opened #13189 to turn it into a regular dependency.

[bluetech]

Personally I have projects which want minimal dependencies so I appreciate that pygments is optional. But I understand that the way it's currently done is not ideal, so I support making it a required dependency.

Hopefully if Python packaging gains the ability to have "default extras" we could switch to that - add a color extra, make it a default but allow people who really want to turn it off. Quick search shows that there is now a draft PEP for this PEP 771 – Default Extras for Python Software Packages so there is hope.

[The-Compiler]

Personally I have projects which want minimal dependencies

I can see wanting to have minimal direct dependencies, and I can see wanting to have minimal runtime dependencies. I think for a transitive dependency that's also development-only, it might be less of an issue?

Hopefully if Python packaging gains the ability to have "default extras" we could switch to that

That would be cool! From looking at python/peps#4198 that's only some 2-3 weeks old, but it would definitely make this kind of thing easier!