Add support for the NO_COLOR environment variable

[akaihola]

pypa/pip#10909 is so far the "highest profile" discussion I've found on this topic.

It seems that pip and colorama are going to support only FORCE_COLOR=<anything> and NO_COLOR=<anything>, but not PY_COLORS.

On the other hand, Pytest does support PY_COLORS={1|0} and NO_COLOR=<anything> (with PY_COLORS taking precedence).

So in the end it may be best to do the same as Pytest:

• PY_COLORS={1|0} (taking precedence over other options)
• NO_COLOR=<anything>
• and possibly FORCE_COLOR=<anything> (similar to pip and colorama)

As for the true/false discussion, I'm going to make the call to only support PY_COLORS={0|1} for now. Thanks @MatthijsBurgh for initiating the discussion and motivating me to look further into the topic!

Originally posted by @akaihola in #353 (comment)

[MatthijsBurgh]

Good job. I can only agree with the suggestion. So you want to keep #353 to only support the PY_COLORS and implement the suggested behavior in a new PR?

[akaihola]

keep #353 to only support the PY_COLORS and implement the suggested behavior in a new PR?

Yes @MatthijsBurgh I think I'd like to have these in separate issues.

The other question then is whether to

• release 1.5.0 without Add support for the NO_COLOR environment variable #355,
• move both Allow user to force syntax highlighting using config file, env var or command line. Enable syntax highlighting in GitHub Action. #353 and Add support for the NO_COLOR environment variable #355 into e.g. the 1.5.1 release
• delay the 1.5.0 release and include both PY_COLORS and NO_COLOR in it

[MatthijsBurgh]

I think option 2/3 is the best one. I think both should be included in the same release. And I think the version should be a minor version bump. So it will be 1.5.0 or 1.6.0 depending on whether you want to wait for this feature or release a version without it for now.