custom rubocop cop for checking if variable names are too short

short_variable_name.rb

# frozen_string_literal: true

# put this file at .rubocop/cop/naming/short_variable_name.rb
# then ensure you have the following in .rubocop.yml:
#
# require:
#   - .rubocop/cop/naming/short_variable_name.rb
# 
# Naming/ShortVariableName:
#   Enabled: true
#   Exclude: 
#     - 'config/initializers/**/*'
#     - 'lib/tasks/**/*'
#     - 'db/**/*'
#     - 'bin/**/*'

module RuboCop
  module Cop
    module Naming
      # This cop checks for variable names that are too short.
      # By default, it requires variable names to be at least 3 characters long.
      # The minimum length and exceptions can be configured.
      # The cop also allows for certain short variable names by default: `i` and `id`.
      #
      # @example
      #   # bad
      #   in = 0
      #   us = 0
      #
      #   # good
      #   index = 0
      #   user = 0
      #
      class ShortVariableName < Base
        include AllowedIdentifiers
        include ConfigurableNaming
        include AllowedPattern

        exclude_limit "Min"

        MSG = "Variable name `%<variable_name>s` is too short (must be at least %<min>d chars long)."

        def on_lvasgn(node)
          name, = *node

          return unless name
          return if name.length >= min
          return if name.to_s.start_with?("_")
          return if exceptions.include?(name.to_s)

          add_offense(node.loc.name, message: message(name))
        end
        alias_method :on_ivasgn, :on_lvasgn
        alias_method :on_cvasgn, :on_lvasgn
        alias_method :on_arg, :on_lvasgn
        alias_method :on_optarg, :on_lvasgn
        alias_method :on_restarg, :on_lvasgn
        alias_method :on_kwoptarg, :on_lvasgn
        alias_method :on_kwarg, :on_lvasgn
        alias_method :on_kwrestarg, :on_lvasgn
        alias_method :on_blockarg, :on_lvasgn
        alias_method :on_lvar, :on_lvasgn

        private

        def message(variable_name)
          format(MSG, variable_name: variable_name, min: min)
        end

        def min
          cop_config.fetch("Min", 3)
        end

        def exceptions
          Array(cop_config["Exceptions"]).presence || ["i", "id"]
        end
      end
    end
  end
end