class RuboCop::Cop::Rails::UnusedIgnoredColumns


end
self.ignored_columns = [:still_existing_column]
class User < ApplicationRecord
# good
end
self.ignored_columns = [:already_removed_column]
class User < ApplicationRecord
# bad
@example
to drop the column. You avoid forgetting to remove ‘ignored_columns` by this cop.
`ignored_columns` is necessary to drop a column from RDBMS, but you don’t need it after the migration
This cop suggests you remove a column that does not exist in the schema from ‘ignored_columns`.

def check_column_existence(column_node, table) 

def check_column_existence(column_node, table)
  column_name = column_name(column_node)
  return unless column_name
  return if table.with_column?(name: column_name.to_s)
  message = format(MSG, column_name: column_name)
  add_offense(column_node, message: message)
end

def class_node(node) 

def class_node(node)
  node.each_ancestor.find(&:class_type?)
end

def on_send(node) 

def on_send(node)
  return unless (columns = ignored_columns(node))
  return unless schema
  table = table(node)
  return unless table
  columns.children.each do |column_node|
    check_column_existence(column_node, table)
  end
end

def table(node) 

def table(node)
  klass = class_node(node)
  schema.table_by(name: table_name(klass))
end