Add section for redundant all

[masato-bkn]

Related issue: #339

This PR adds "Redundant all" section.

[pirj]

Is it only applicable to the model or to a relation as well? ‘current_user.likes.all’?

[masato-bkn]

this applies to relation as well.

# bad
current_user.likes.all.order(:created_at)

# good
current_user.likes.order(:created_at)

However, it's uncertain whether this rule can be applied to current_user.likes.all.
In RuboCop, determining whether likes is a relation can be difficult since there are no Active Record query methods following all. If likes is not a relation, removing all might change the result.

[koic]

True, examples of all method followed by an AR query method could be added.

[masato-bkn]

@koic

True, examples of all method followed by an AR query method could be added.

Sorry for the confusion, but I want to make sure I understand your comment correctly.
Are you suggesting that I should add one or both of the following examples?

(like is a relation of User)

1. relation.all.ar_query_method

# bad
current_user.likes.all.order(:created_at)

# good
current_user.likes.order(:created_at)

2. relation.ar_query_method.all

# bad
current_user.likes.order(:created_at).all

# good
current_user.likes.order(:created_at)

[koic]

I imagined it as 1. Either way, the receiver is an ActiveRecord_Relation object.

[masato-bkn]

Thank you for your comment. I've added some examples.

[koic]

@masato-bkn Can you squash your commits into one?

[masato-bkn]

@koic
I've squashed the commits!

[koic]

Thanks!