Cop Idea: `ApplicationRecord`: delegation of `to_s` to attributes

[tagliala]

⚠️ Disclaimer: please double check if this proposal makes sense

Is your feature request related to a problem? Please describe.

It is common for ApplicationRecord classes to define their own to_s method, for example, as seen here:

def to_s
  name # or title, or email...
end

However, this can violate the Principle of Least Astonishment (PoLA), as calling to_s on a newly instantiated object may return nil instead of a string.

By using delegate :to_s, to: :name instead, the method will consistently return an empty string when the attribute is nil, ensuring that to_s always returns a string.

Describe the solution you'd like

A cop should suggest the following change:

-def to_s
-  name
-end
+delegate :to_s, to: :name

Additional context

This is already the case for properly implemented to_s methods:

• Rails/Delegate Cop will turn name.to_s to delegate...
• Style/RedundantInterpolation will turn "#{name}" into delegate... with an intermediate name.to_s

Examples:

# ...
def to_s
  name.to_s
end
# ...

user.rb:4:3: C: [Correctable] Rails/Delegate: Use delegate to define delegations.
  def to_s
  ^^^

# ...
def to_s
  "#{name}"
end
# ...

user.rb:5:5: C: [Correctable] Style/RedundantInterpolation: Prefer to_s over string interpolation.
    "#{name}"