[Swift 5.0]: LowerACLThanParentRule is broken

[jpsim]

private class Foo { func bar() {} }
                    ^ warning: Lower ACL than parent Violation: Ensure definitions have a lower access control level than their enclosing parent (lower_acl_than_parent)

It seems like members without an explicit ACL annotation in Swift 5 are incorrectly assumed to be internal. This causes incorrect violations in Swift 5 that aren't present in Swift 4.x.

[jpsim]

I filed SR-9777 to track this.

[marcelofabri]

We could work around it for this rule in specific and check the annotations instead (as we don't really care about implicit ACLs here).

It'd be great to fix it on SourceKit though to avoid any surprises on other rules.