Color output not shown in CI

[asmeurer]

Describe the bug

This is a spinoff of #13056

I have to add FORCE_COLOR=1 to my Makefile to force color output on CircleCI and GitHub Actions.

Here is an example of a build with the default options and no color output: https://github.com/Quansight-Labs/ndindex/actions/runs/11253438088/job/31288699625

Here is an example where I've set FORCE_COLOR=1 (from a different project): https://github.com/sympy/sympy/actions/runs/11484600101/job/31963800399

The color output makes things much easier to read, especially if there is a warning or error printed in red.

How to Reproduce

Run a Sphinx build on GitHub Actions

Environment Information

See the build log above. Seems to be installing Sphinx 8.0.2

Sphinx extensions

No response

Additional context

We should investigate why this happens. It isn't clear to me if this is just a limitation of CI systems or if there is something else at play here. What do other tools that output color on CI do? Are they manually enabling color when they detect they are on GitHub Actions? Is the fact that Sphinx is run through make relevant?

Obviously we don't want to unconditionally enable color output in Sphinx, especially when the output is a pipe.

[AA-Turner]

The relevant code is

sphinx/sphinx/util/console.py

Lines 94 to 109 in 8042eb6

	def color_terminal() -> bool:
	if 'NO_COLOR' in os.environ:
	return False
	if sys.platform == 'win32' and COLORAMA_AVAILABLE:
	colorama.just_fix_windows_console()
	return True
	if 'FORCE_COLOR' in os.environ:
	return True
	if not hasattr(sys.stdout, 'isatty'):
	return False
	if not sys.stdout.isatty():
	return False
	if 'COLORTERM' in os.environ:
	return True
	term = os.environ.get('TERM', 'dumb').lower()
	return term in {'xterm', 'linux'} or 'color' in term

My assumption is that it fails because CI is not a TTY. But as you say, perhaps we can improve this logic.

A

[asmeurer]

Here is the logic from a Rust package https://github.com/zkat/is_ci/blob/main/src/lib.rs

This is used in the Rust supports-color package https://github.com/zkat/supports-color/blob/main/src/lib.rs