console: auto activate ansi colors in github actions

[staabm]

Symfony version(s) affected: 4.x

Description
Github Actions added support for ansi colors recently.

it turns out that symfony console based apps don't auto-enable syntax coloring.
initially I had reported this issue on composer/composer#9269 but jordi would instead want a fix in symfony/console and/or Github Actions instead.

therefore I also opened a issue on the Github actions runner, without feedback yet though
actions/runner#750

to get fancy colors on github actions, we need to manually enable ..ansi which is tedious:
see e.g. https://github.com/redaxo/redaxo/pull/3939/files

How to reproduce

run composer install within a github action

Possible Solution
imply --ansi when false !== getenv('GITHUB_ACTION')

Additional context
people work arround this problem by sprinkling additional --ansi flags across all the php based tools invoked within github action already, see e.g. https://tomasvotruba.com/blog/2020/09/28/how-to-add-colors-to-continuious-integration-output/

[derrabus]

imply --ansi when false !== getenv('GITHUB_ACTION')

Is there a way we could auto-detect color support without building a workaround specific to GitHub actions? I understand that this is kind of what you're asking in actions/runner#750 already.

I don't feel confident about solely relying on that env variable. One scenario I could imagine here: You would use the Process component to run another Symfony Console based tool (e.g. your tool calls Composer for certain tasks). In that case the env variable would still be set, but auto-enabling color output is probably not desirable in that context.

[stof]

env-based detection are a bad idea. they would break scripts running things like some-comment > output.txt, as it would consider that output.txt supports ANSI colors...

[chalasr]

I'm closing this issue as the proposed solution does not look right. This would better be solved on GA' side to me.