lib/rubocop/cop/style/empty_literal.rb
# frozen_string_literal: true
module RuboCop
module Cop
module Style
# Checks for the use of a method, the result of which
# would be a literal, like an empty array, hash, or string.
#
# @example
# # bad
# a = Array.new
# h = Hash.new
# s = String.new
#
# # good
# a = []
# h = {}
# s = ''
class EmptyLiteral < Base
include FrozenStringLiteral
include RangeHelp
extend AutoCorrector
ARR_MSG = 'Use array literal `[]` instead of `Array.new`.'
HASH_MSG = 'Use hash literal `{}` instead of `Hash.new`.'
STR_MSG = 'Use string literal `%<prefer>s` instead of `String.new`.'
RESTRICT_ON_SEND = %i[new].freeze
# @!method array_node(node)
def_node_matcher :array_node, '(send (const {nil? cbase} :Array) :new)'
# @!method hash_node(node)
def_node_matcher :hash_node, '(send (const {nil? cbase} :Hash) :new)'
# @!method str_node(node)
def_node_matcher :str_node, '(send (const {nil? cbase} :String) :new)'
# @!method array_with_block(node)
def_node_matcher :array_with_block, '(block (send (const {nil? cbase} :Array) :new) args _)'
# @!method hash_with_block(node)
def_node_matcher :hash_with_block, <<~PATTERN
{
(block (send (const {nil? cbase} :Hash) :new) args _)
(numblock (send (const {nil? cbase} :Hash) :new) ...)
}
PATTERN
def on_send(node)
return unless (message = offense_message(node))
add_offense(node, message: message) do |corrector|
corrector.replace(replacement_range(node), correction(node))
end
end
private
def offense_message(node)
if offense_array_node?(node)
ARR_MSG
elsif offense_hash_node?(node)
HASH_MSG
elsif str_node(node) && !frozen_strings?
format(STR_MSG, prefer: preferred_string_literal)
end
end
def preferred_string_literal
enforce_double_quotes? ? '""' : "''"
end
def enforce_double_quotes?
string_literals_config['EnforcedStyle'] == 'double_quotes'
end
def string_literals_config
config.for_cop('Style/StringLiterals')
end
def first_argument_unparenthesized?(node)
parent = node.parent
return false unless parent && %i[send super zsuper].include?(parent.type)
node.equal?(parent.first_argument) && !parentheses?(node.parent)
end
def replacement_range(node)
if hash_node(node) && first_argument_unparenthesized?(node)
# `some_method {}` is not same as `some_method Hash.new`
# because the braces are interpreted as a block. We will have
# to rewrite the arguments to wrap them in parenthesis.
args = node.parent.arguments
range_between(args[0].source_range.begin_pos - 1, args[-1].source_range.end_pos)
else
node.source_range
end
end
def offense_array_node?(node)
array_node(node) && !array_with_block(node.parent)
end
def offense_hash_node?(node)
# If Hash.new takes a block, it can't be changed to {}.
hash_node(node) && !hash_with_block(node.parent)
end
def correction(node)
if offense_array_node?(node)
'[]'
elsif str_node(node)
preferred_string_literal
elsif offense_hash_node?(node)
if first_argument_unparenthesized?(node)
# `some_method {}` is not same as `some_method Hash.new`
# because the braces are interpreted as a block. We will have
# to rewrite the arguments to wrap them in parenthesis.
args = node.parent.arguments
"(#{args[1..].map(&:source).unshift('{}').join(', ')})"
else
'{}'
end
end
end
def frozen_strings?
return true if frozen_string_literals_enabled?
frozen_string_cop_enabled = config.for_cop('Style/FrozenStringLiteral')['Enabled']
frozen_string_cop_enabled && !frozen_string_literals_disabled?
end
end
end
end
end