`X = Struct.new(:x) do` is bad

The style guide suggest to use

X = Struct.new(:x) do
  def method
  end
end

# instead of

class Y < Struct.new(:y)
  def method
  end
end

I think this is a bad recommendation. Yes, the later creates an unnecessary anonymous class, but it uses the usual syntax to create classes and thus is easy to understand. Even Rubocop doesn't recognize the assignment syntax everywhere (E.g. Style/Documentation doesn't care about this).

Also, this leads to hard to understand errors:

X = Struct.new(:x) do
  XX = true
end

defined?(X::XX) # => nil
defined?(XX) # => "constant"

class Y < Struct.new(:y)
  YY = true
end

defined?(Y::YY) # => "constant"
defined?(YY) # => nil

This is possible, but is it better?

Z = Struct.new(:z)
class Z
  ZZ = true
end

defined?(Z::ZZ) # => "constant"
defined?(ZZ) # => nil

Review the style guide recommendation about assigning Struct.new and compare it with the alternative class syntax and the Style/Documentation behavior cited in the issue. Decide whether the recommendation should change, and document the chosen guidance with examples that make constant behavior and readability clear.