Added config validation

[evertharmeling]

Currently with the following config:

symfonycasts_sass:
    root_sass:
        - '%kernel.project_dir%/assets/admin/scss/app.scss'
        - '%kernel.project_dir%/assets/website/scss/app.scss'

Running the sass:build command would result all configured paths to be build in 1 file; var/sass/app.output.css, as all root_sass paths with the same filename will be stored under the same css filename, thus overwriting the file.

This PR throws an exception when configuring the sass-paths. (follow-up on #30)

[bocharsky-bw]

What is the purpose of this? I don't think it's needed, because we don't use it as a dependency and install it via third-party on CI. Locally, it's probably a good idea to have it installed globally, not per project.

In other words, we don't "depend" on those libs directly, they are just used on CI to help, but nothing more. It seems best practice to not require it in composer.json anymore. Actually, I think the same relates to PHPStan as well, we can completely remove those 2 libs and if CI is happy - double win, fewer dependencies.

[evertharmeling]

The idea was to prevent checks to fail before a PR was created and since phpstan was already a dev-dependency, but changed it.

I've now added only phpstan/phpstan-symfony as requested.

[bocharsky-bw]

Though probably if we want to link this directly from the vendor - it may require the phpstan/phpstan-symfony pack, but probably only that one, phpstan/phpstan is redundant I think.

Btw, I suppose this line fixed that ignored error message you deleted below, right?

[evertharmeling]

Yes it did :)

[bocharsky-bw]

Hm, I'm not sure this solution is robust enough... it works for 2 files, but with more files it will not work because it only reveals duplicates that are going consequently.

I think we need to collect all the filenames in an array, and every time check if that array already contains the currently handled filename. It should be more robust, but still it might be a possible problem later if the upstream logic changed :/

[evertharmeling]

Thanks for (again) being sharper than me, fixed it and even added tests for the configuration

[bocharsky-bw]

Thanks for adding some tests! I like this, just a minor error message tweak

[bocharsky-bw]

Thank you