lib/rubocop/cop/lint/void.rb
# frozen_string_literal: true
module RuboCop
module Cop
module Lint
# Checks for operators, variables, literals, lambda, proc and nonmutating
# methods used in void context.
#
# `each` blocks are allowed to prevent false positives.
# For example, the expression inside the `each` block below.
# It's not void, especially when the receiver is an `Enumerator`:
#
# [source,ruby]
# ----
# enumerator = [1, 2, 3].filter
# enumerator.each { |item| item >= 2 } #=> [2, 3]
# ----
#
# @example CheckForMethodsWithNoSideEffects: false (default)
# # bad
# def some_method
# some_num * 10
# do_something
# end
#
# def some_method(some_var)
# some_var
# do_something
# end
#
# @example CheckForMethodsWithNoSideEffects: true
# # bad
# def some_method(some_array)
# some_array.sort
# do_something(some_array)
# end
#
# # good
# def some_method
# do_something
# some_num * 10
# end
#
# def some_method(some_var)
# do_something
# some_var
# end
#
# def some_method(some_array)
# some_array.sort!
# do_something(some_array)
# end
class Void < Base
extend AutoCorrector
include RangeHelp
OP_MSG = 'Operator `%<op>s` used in void context.'
VAR_MSG = 'Variable `%<var>s` used in void context.'
CONST_MSG = 'Constant `%<var>s` used in void context.'
LIT_MSG = 'Literal `%<lit>s` used in void context.'
SELF_MSG = '`self` used in void context.'
EXPRESSION_MSG = '`%<expression>s` used in void context.'
NONMUTATING_MSG = 'Method `#%<method>s` used in void context. Did you mean `#%<suggest>s`?'
BINARY_OPERATORS = %i[* / % + - == === != < > <= >= <=>].freeze
UNARY_OPERATORS = %i[+@ -@ ~ !].freeze
OPERATORS = (BINARY_OPERATORS + UNARY_OPERATORS).freeze
VOID_CONTEXT_TYPES = %i[def for block].freeze
NONMUTATING_METHODS_WITH_BANG_VERSION = %i[capitalize chomp chop compact
delete_prefix delete_suffix downcase
encode flatten gsub lstrip merge next
reject reverse rotate rstrip scrub select
shuffle slice sort sort_by squeeze strip sub
succ swapcase tr tr_s transform_values
unicode_normalize uniq upcase].freeze
METHODS_REPLACEABLE_BY_EACH = %i[collect map].freeze
NONMUTATING_METHODS = (NONMUTATING_METHODS_WITH_BANG_VERSION +
METHODS_REPLACEABLE_BY_EACH).freeze
def on_block(node)
return unless node.body && !node.body.begin_type?
return unless in_void_context?(node.body)
check_void_op(node.body) { node.method?(:each) }
check_expression(node.body)
end
alias on_numblock on_block
def on_begin(node)
check_begin(node)
end
alias on_kwbegin on_begin
private
def check_begin(node)
expressions = *node
expressions.pop unless in_void_context?(node)
expressions.each do |expr|
check_void_op(expr) do
block_node = node.each_ancestor(:block).first
block_node&.method?(:each)
end
check_expression(expr)
end
end
def check_expression(expr)
check_literal(expr)
check_var(expr)
check_self(expr)
check_void_expression(expr)
return unless cop_config['CheckForMethodsWithNoSideEffects']
check_nonmutating(expr)
end
def check_void_op(node, &block)
return unless node.send_type? && OPERATORS.include?(node.method_name)
return if block && yield(node)
add_offense(node.loc.selector,
message: format(OP_MSG, op: node.method_name)) do |corrector|
autocorrect_void_op(corrector, node)
end
end
def check_var(node)
return unless node.variable? || node.const_type?
if node.const_type?
template = node.special_keyword? ? VAR_MSG : CONST_MSG
offense_range = node
message = format(template, var: node.source)
else
offense_range = node.loc.name
message = format(VAR_MSG, var: node.loc.name.source)
end
add_offense(offense_range, message: message) do |corrector|
autocorrect_void_expression(corrector, node)
end
end
def check_literal(node)
return if !entirely_literal?(node) || node.xstr_type? || node.range_type?
add_offense(node, message: format(LIT_MSG, lit: node.source)) do |corrector|
autocorrect_void_expression(corrector, node)
end
end
def check_self(node)
return unless node.self_type?
add_offense(node, message: SELF_MSG) do |corrector|
autocorrect_void_expression(corrector, node)
end
end
def check_void_expression(node)
return unless node.defined_type? || node.lambda_or_proc?
add_offense(node, message: format(EXPRESSION_MSG, expression: node.source)) do |corrector|
autocorrect_void_expression(corrector, node)
end
end
def check_nonmutating(node)
return if !node.send_type? && !node.block_type? && !node.numblock_type?
method_name = node.method_name
return unless NONMUTATING_METHODS.include?(method_name)
suggestion = if METHODS_REPLACEABLE_BY_EACH.include?(method_name)
'each'
else
"#{method_name}!"
end
add_offense(node,
message: format(NONMUTATING_MSG, method: method_name,
suggest: suggestion)) do |corrector|
autocorrect_nonmutating_send(corrector, node, suggestion)
end
end
def in_void_context?(node)
parent = node.parent
return false unless parent && parent.children.last == node
VOID_CONTEXT_TYPES.include?(parent.type) && parent.void_context?
end
def autocorrect_void_op(corrector, node)
if node.arguments.empty?
corrector.replace(node, node.receiver.source)
else
corrector.replace(
range_with_surrounding_space(range: node.loc.selector, side: :both,
newlines: false),
"\n"
)
end
end
def autocorrect_void_expression(corrector, node)
corrector.remove(range_with_surrounding_space(range: node.source_range, side: :left))
end
def autocorrect_nonmutating_send(corrector, node, suggestion)
send_node = if node.send_type?
node
else
node.send_node
end
corrector.replace(send_node.loc.selector, suggestion)
end
def entirely_literal?(node)
case node.type
when :array
node.each_value.all? { |value| entirely_literal?(value) }
when :hash
return false unless node.each_key.all? { |key| entirely_literal?(key) }
node.each_value.all? { |value| entirely_literal?(value) }
else
node.literal?
end
end
end
end
end
end