class RuboCop::Cop::Bundler::DuplicatedGem

gem ‘rubocop’, groups: [:development, :test]
# good
end
gem ‘rubocop’
group :development, :test do
# good
end
gem ‘rubocop’
group :test do
end
gem ‘rubocop’
group :development do
# bad
gem ‘rubocop’
gem ‘rubocop’
# bad
@example
A Gem’s requirements should be listed only once in a Gemfile.

def duplicated_gem_nodes 

def duplicated_gem_nodes
  gem_declarations(processed_source.ast)
    .group_by { |e| e.method_args.first }
    .keep_if { |_, nodes| nodes.length > 1 }
    .values
end

def investigate(processed_source) 

def investigate(processed_source)
  return unless processed_source.ast
  duplicated_gem_nodes.each do |nodes|
    nodes[1..-1].each do |node|
      register_offense(
        node,
        node.method_args.first.to_a.first,
        nodes.first.loc.line
      )
    end
  end
end

def register_offense(node, gem_name, line_of_first_occurence) 

def register_offense(node, gem_name, line_of_first_occurence)
  line_range = node.loc.column...node.loc.last_column
  add_offense(
    node,
    source_range(processed_source.buffer, node.loc.line, line_range),
    format(MSG, gem_name, line_of_first_occurence)
  )
end