Fix: Collect and report code coverage

[localheinz]

This PR

• requires PHP 7.2 in generator/composer.json
• requires phpunit/phpunit:^8.5.2
• sets up PHP with the pcov extension enabled
• enables step related to archiving and reporting code coverage

Follows #191 (comment).

💁‍♂ The update to PHP 7.2 allows us to install phpunit/phpunit:^8, which has support for collecting code coverage with pcov, which in turn is a lot faster than using Xdebug.

[localheinz]

@Kharhamel

The checkout with svn appears to be a bit flaky.

Perhaps it makes sense to switch to using the mirror at https://github.com/php/doc-en instead?

[localheinz]

@Kharhamel

Needs some work on the tests - will fix after dinner!

[localheinz]

The secret COVERALLS_REPO_TOKEN needs to be provided.

However, secrets will not be available when actions are triggered by actors who do not have write privileges. That's why I added continue-on-error here.

For reference, see:

• https://github.com/php-coveralls/php-coveralls#from-local-environment
• https://help.github.com/en/actions/configuring-and-managing-workflows/creating-and-storing-encrypted-secrets
• https://help.github.com/en/actions/reference/workflow-syntax-for-github-actions#jobsjob_idstepscontinue-on-error

[Kharhamel]

That means that anyone other than moufmouf or me will not benefit from the code coverage report.
That makes it kinda useless. Could we not use the option --dry-run to do the report locally and make it create an error if the code coverage goes down?

[Kharhamel]

maybe see coverallsapp/github-action#15

[moufmouf]

Hey @localheinz ,

Thanks a lot for this PR. I think we will put the COVERALLS_REPO_TOKEN environment variable in clear directly in the repo (so that we get code coverage from the forks too). It's never good to put a secret publicly, but that's "only" a secret for Coveralls.

[localheinz]

Thank you, @Kharhamel and @moufmouf!