The GitHub action for Darker doesn't use syntax highlighting

[mayk0gan]

Currently, you run:
proc = subprocess.run([sys.executable, str(MAIN_SCRIPT)]);
in the github action.

It doesn't output any colors, which makes it harder to understand darker's output.
You could use something like written here: https://stackoverflow.com/questions/58307157/subprocess-call-output-in-color printing the output with colors.

[akaihola]

Thanks @mayk0gan, I will consider that and return to this suggestion a bit later.

[akaihola]

@mayk0gan, as far as I understand, the solution for subprocess.call output in color on Stack Overflow captures all output and prints it all in one color.

I would assume you'd prefer to have Darker's original output colors intact in the GitHub Action output instead? Do you have an idea of how to achieve that?

Jeff Geerling's blog post Getting colorized output from Molecule and Ansible on GitHub Actions for CI suggests to me that GitHub Actions actually will convert TTY ANSI color codes to HTML colors, and the problem here is only that Darker assumes the output is not to a TTY and will thus disable colors.

So maybe a command line option or environment variable to force color output would suffice?
Black has:

  --color / --no-color            Show colored diff. Only applies when
                                  `--diff` is given.

On the other hand, Jeff writes:

• PY_COLORS: This is a somewhat standard way to tell Python-based tools to force color output, even without TTY.

The two places in Darker code which decide between color and raw output are

• darker.__main__.print_source()
• darker.highlighting.with_pygments.colorize()

[akaihola]

@mayk0gan I can include Darker color output in the GitHub Action in release 1.5.0 if you think that would make sense and if you can lend your hand a bit by testing and discussing the design choices mentioned above.