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# frozen_string_literal: true
module RuboCop
module Cop
module Performance
# This cop identifies places where a case-insensitive string comparison
# can better be implemented using `casecmp`.
#
# @example
# # bad
# str.downcase == 'abc'
# str.upcase.eql? 'ABC'
# 'abc' == str.downcase
# 'ABC'.eql? str.upcase
# str.downcase == str.downcase
#
# # good
# str.casecmp('ABC').zero?
# 'abc'.casecmp(str).zero?
class Casecmp < Cop
MSG = 'Use `%<good>s` instead of `%<bad>s`.'.freeze
CASE_METHODS = %i[downcase upcase].freeze
def_node_matcher :downcase_eq, <<-PATTERN
(send
$(send _ ${:downcase :upcase})
${:== :eql? :!=}
${str (send _ {:downcase :upcase} ...) (begin str)})
PATTERN
def_node_matcher :eq_downcase, <<-PATTERN
(send
{str (send _ {:downcase :upcase} ...) (begin str)}
${:== :eql? :!=}
$(send _ ${:downcase :upcase}))
PATTERN
def_node_matcher :downcase_downcase, <<-PATTERN
(send
$(send _ ${:downcase :upcase})
${:== :eql? :!=}
$(send _ ${:downcase :upcase}))
PATTERN
def on_send(node)
return unless downcase_eq(node) || eq_downcase(node)
return unless (parts = take_method_apart(node))
_, _, arg, variable = parts
good_method = build_good_method(arg, variable)
add_offense(
node,
message: format(MSG, good: good_method, bad: node.source)
)
end
def autocorrect(node)
return unless (parts = take_method_apart(node))
receiver, method, arg, variable = parts
correction(node, receiver, method, arg, variable)
end
private
def take_method_apart(node)
if downcase_downcase(node)
receiver, method, rhs = *node
arg, = *rhs
elsif downcase_eq(node)
receiver, method, arg = *node
elsif eq_downcase(node)
arg, method, receiver = *node
else
return
end
variable, = *receiver
[receiver, method, arg, variable]
end
def correction(node, _receiver, method, arg, variable)
lambda do |corrector|
corrector.insert_before(node.loc.expression, '!') if method == :!=
replacement = build_good_method(arg, variable)
corrector.replace(node.loc.expression, replacement)
end
end
def build_good_method(arg, variable)
# We want resulting call to be parenthesized
# if arg already includes one or more sets of parens, don't add more
# or if method call already used parens, again, don't add more
if arg.send_type? || !parentheses?(arg)
"#{variable.source}.casecmp(#{arg.source}).zero?"
else
"#{variable.source}.casecmp#{arg.source}.zero?"
end
end
end
end
end
end
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