lib/rubocop/cop/lint/self_assignment.rb
# frozen_string_literal: true
module RuboCop
module Cop
module Lint
# Checks for self-assignments.
#
# @example
# # bad
# foo = foo
# foo, bar = foo, bar
# Foo = Foo
# hash['foo'] = hash['foo']
# obj.attr = obj.attr
#
# # good
# foo = bar
# foo, bar = bar, foo
# Foo = Bar
# hash['foo'] = hash['bar']
# obj.attr = obj.attr2
#
# # good (method calls possibly can return different results)
# hash[foo] = hash[foo]
#
class SelfAssignment < Base
MSG = 'Self-assignment detected.'
ASSIGNMENT_TYPE_TO_RHS_TYPE = {
lvasgn: :lvar,
ivasgn: :ivar,
cvasgn: :cvar,
gvasgn: :gvar
}.freeze
def on_send(node)
if node.method?(:[]=)
handle_key_assignment(node) if node.arguments.size == 2
elsif node.assignment_method?
handle_attribute_assignment(node) if node.arguments.size == 1
end
end
alias on_csend on_send
def on_lvasgn(node)
lhs, rhs = *node
return unless rhs
rhs_type = ASSIGNMENT_TYPE_TO_RHS_TYPE[node.type]
add_offense(node) if rhs.type == rhs_type && rhs.source == lhs.to_s
end
alias on_ivasgn on_lvasgn
alias on_cvasgn on_lvasgn
alias on_gvasgn on_lvasgn
def on_casgn(node)
lhs_scope, lhs_name, rhs = *node
return unless rhs&.const_type?
rhs_scope, rhs_name = *rhs
add_offense(node) if lhs_scope == rhs_scope && lhs_name == rhs_name
end
def on_masgn(node)
add_offense(node) if multiple_self_assignment?(node)
end
def on_or_asgn(node)
lhs, rhs = *node
add_offense(node) if rhs_matches_lhs?(rhs, lhs)
end
alias on_and_asgn on_or_asgn
private
def multiple_self_assignment?(node)
lhs, rhs = *node
return false unless rhs.array_type?
return false unless lhs.children.size == rhs.children.size
lhs.children.zip(rhs.children).all? do |lhs_item, rhs_item|
rhs_matches_lhs?(rhs_item, lhs_item)
end
end
def rhs_matches_lhs?(rhs, lhs)
rhs.type == ASSIGNMENT_TYPE_TO_RHS_TYPE[lhs.type] &&
rhs.children.first == lhs.children.first
end
def handle_key_assignment(node)
value_node = node.arguments[1]
if value_node.send_type? && value_node.method?(:[]) &&
node.receiver == value_node.receiver &&
!node.first_argument.call_type? &&
node.first_argument == value_node.first_argument
add_offense(node)
end
end
def handle_attribute_assignment(node)
first_argument = node.first_argument
return unless first_argument.respond_to?(:arguments) && first_argument.arguments.empty?
if first_argument.call_type? &&
node.receiver == first_argument.receiver &&
first_argument.method_name.to_s == node.method_name.to_s.delete_suffix('=')
add_offense(node)
end
end
end
end
end
end