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numeric_predicate.rb
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numeric_predicate.rb
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# frozen_string_literal: true
module RuboCop
module Cop
module Style
# This cop checks for usage of comparison operators (`==`,
# `>`, `<`) to test numbers as zero, positive, or negative.
# These can be replaced by their respective predicate methods.
# The cop can also be configured to do the reverse.
#
# The cop disregards `#nonzero?` as it its value is truthy or falsey,
# but not `true` and `false`, and thus not always interchangeable with
# `!= 0`.
#
# The cop ignores comparisons to global variables, since they are often
# populated with objects which can be compared with integers, but are
# not themselves `Integer` polymorphic.
#
# @example EnforcedStyle: predicate (default)
# # bad
#
# foo == 0
# 0 > foo
# bar.baz > 0
#
# # good
#
# foo.zero?
# foo.negative?
# bar.baz.positive?
#
# @example EnforcedStyle: comparison
# # bad
#
# foo.zero?
# foo.negative?
# bar.baz.positive?
#
# # good
#
# foo == 0
# 0 > foo
# bar.baz > 0
class NumericPredicate < Cop
include ConfigurableEnforcedStyle
include IgnoredMethods
MSG = 'Use `%<prefer>s` instead of `%<current>s`.'
REPLACEMENTS = {
'zero?' => '==',
'positive?' => '>',
'negative?' => '<'
}.freeze
COMPARISON_METHODS = %i[== > < positive? negative? zero?].to_set.freeze
def on_send(node)
return unless COMPARISON_METHODS.include?(node.method_name)
numeric, replacement = check(node)
return unless numeric
return if ignored_method?(node.method_name) ||
node.each_ancestor(:send, :block).any? do |ancestor|
ignored_method?(ancestor.method_name)
end
add_offense(node,
message: format(MSG,
prefer: replacement,
current: node.source))
end
def autocorrect(node)
_, replacement = check(node)
lambda do |corrector|
corrector.replace(node, replacement)
end
end
private
def check(node)
numeric, operator =
if style == :predicate
comparison(node) || inverted_comparison(node, &invert)
else
predicate(node)
end
return unless numeric && operator
[numeric, replacement(numeric, operator)]
end
def replacement(numeric, operation)
if style == :predicate
[parenthesized_source(numeric),
REPLACEMENTS.invert[operation.to_s]].join('.')
else
[numeric.source, REPLACEMENTS[operation.to_s], 0].join(' ')
end
end
def parenthesized_source(node)
if require_parentheses?(node)
"(#{node.source})"
else
node.source
end
end
def require_parentheses?(node)
node.send_type? && node.binary_operation? && !node.parenthesized?
end
def invert
lambda do |comparison, numeric|
comparison = { :> => :<, :< => :> }[comparison] || comparison
[numeric, comparison]
end
end
def_node_matcher :predicate, <<~PATTERN
(send $(...) ${:zero? :positive? :negative?})
PATTERN
def_node_matcher :comparison, <<~PATTERN
(send [$(...) !gvar_type?] ${:== :> :<} (int 0))
PATTERN
def_node_matcher :inverted_comparison, <<~PATTERN
(send (int 0) ${:== :> :<} [$(...) !gvar_type?])
PATTERN
end
end
end
end