Suggest rule: Class cannot be public.

[VovaStelmashchuk]

I suggest add rule: Class cannot be publish.

I need the rule in the following case: Inside library and i want to sure all my class are internal or private, exclude API classes. We have this rule in custom company rule set. We want to contribute the rule to origin project, like an optional rule. Maybe someone need this rule too.

Are rule valid to be in the origin project?

We already discussed issue in KtLint pinterest/ktlint#795
I migrate my project to Detekt at the moment.

[arturbosch]

Hi @VovaStelmashchuk ,
this sounds like a really good rule for library authors, thanks for the suggestion.
You can take a look at the LibraryCodeMustSpecifyReturnType rule how we achieved to only run the rule if specific filters are active.
This is how we expect the users to configure it:

detekt/config/detekt/detekt.yml

Lines 116 to 119 in 66c9afe

	LibraryCodeMustSpecifyReturnType:
	active: true
	excludes: ['**/*.kt']
	includes: ['**/detekt-api/src/main/**/api/*.kt']

Looking forward to your PR!