New rule: consider_making_a_member_private (if its not used outside)

[danylo-safonov-solid]

This'll help with dead_code

BAD:

class X {
 // only used internally 
 void x() {
 ...
 }
}

GOOD:

class X {
 // only used internally 
 void _x() {
 ...
 }
}

[kvenn]

I'm very excited for this one! I could see it being very valuable for any class members. For some reason, Dart doesn't recognize that a member is unused unless it's private. So this would be a double whammy if it enforced all members that could be public were public.

[gbassisp]

Should this only be applied to class members? What about top-level ones and class definitions themselves? I think it would be worth having it to all definitions, because top-level functions that are only used internally also add noise to code completion. As a bonus, it could help us identify unused definitions (something that I used to do with dart code metrics).

[illia-romanenko]

@kevmoo just published a new package that is related to this rule: https://pub.dev/packages/undead. What is proposed here is probably slightly different from this new package, but let's think about how it affects this request and whether depending on undead or other Kevin's work will make better sense.

I also asked to add a new section of Notable 3rd party libraries to https://lints.solid.software/docs/intro @solid-illiaaihistov - Kevin's work definitely should be at least added there, as it's very relevant to what we are doing here.

[kevmoo]

Ooo! @illia-romanenko you gave me an IDEA.

I bet my undead code "knows" enough to recommend to make things private. This is a GREAT idea!

[kevmoo]

kevmoo/analytica.dart#44
kevmoo/analytica.dart#45