Github actions can write errors and warning directly in their output, which result into annotations into the Github checks. It can even provide a filename, line & col number, allowing to display the annnotations inside the PR diff directly, at the right place.

More advanced usage of annotations can be made using the API, but regarding the linters provided in Symfony components, it seems the shortcut using output is a great way to enhance the integration with Github Actions.

This PR starts by proposing these changes in the yaml linter:

• add the github format, which is the same as the txt one, except for errors and warning, for which we'll adapt the output to the Github annotations format.
• remove the txt format as default, and autodetect if the script is running in a Github action context, then use github format. If it's not, we fallback to txt as before.

Once we agree on the details, we could perform the same for other linters (xliff, twig, ...)

Here is a PR using it: ogizanagi/symfony-lint-gha-demo#2

and some screenshots:

PR checks run	PR checks annotations	PR diff

(tests to add)

This was inspired by PHPStan which is already auto-adapting the output according to the CI, using https://github.com/OndraM/ci-detector