Enable FORCE_COLOR and NO_COLOR for terminal colouring

[hugovk]

Subject: Allow these widely-used environment variables to improve readability of output

Feature or Bugfix

• Feature

Purpose

Colour can help diagnose problems, and a common place for Sphinx and the need to diagnose problems is on a CI.

However, because GitHub Actions doesn't use a tty, output of tools which autodetect the terminal output is usually monochrome.

Normally you only want to enable colour on a tty, because if you're piping data between commands (not a tty) the colour codes can mess up parsing of piped output. But that's not the case here.

That's why many tools and CI setups use the FORCE_COLOR environment variable, and/or command-line options to turn it back on.

Other tools for reference:

• pytest issue, PR and docs
• nox issue and PR
• tox PR
• pypa/build PR
• Colorama WIP PR
• Node.js docs

Detail

• Like other tools, NO_COLOR takes precedence
• Keep the Windows-specific check before because it initialises colorama
• FORCE_COLOR next

Relates

• https://no-color.org/

[tk0miya]

LGTM. Could you add mentions for these envvars to doc/man/sphinx-build.rst too?

[hugovk]

Added: https://sphinx--10260.org.readthedocs.build/en/10260/man/sphinx-build.html#environment-variables

[ssbarnea]

After digging for few good number of minutes about why sphinx does not use colors i reached this one.

Yes, current cli arguments are not automation/scripting friendly and we are much better reusing existing standard variables for controlling the colors.

[ssbarnea]

@tk0miya Can you please have another look, it seems fixed. I am really eager to get this fix in especially as the older tox trick with {tty:--color} no longer works, for the same reasons. TTY is not the same as supporting color or not.

[tk0miya]

Thank you for your update. Merging now!