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redundant_sort.rb
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redundant_sort.rb
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# frozen_string_literal: true
module RuboCop
module Cop
module Style
# This cop is used to identify instances of sorting and then
# taking only the first or last element. The same behavior can
# be accomplished without a relatively expensive sort by using
# `Enumerable#min` instead of sorting and taking the first
# element and `Enumerable#max` instead of sorting and taking the
# last element. Similarly, `Enumerable#min_by` and
# `Enumerable#max_by` can replace `Enumerable#sort_by` calls
# after which only the first or last element is used.
#
# @example
# # bad
# [2, 1, 3].sort.first
# [2, 1, 3].sort[0]
# [2, 1, 3].sort.at(0)
# [2, 1, 3].sort.slice(0)
#
# # good
# [2, 1, 3].min
#
# # bad
# [2, 1, 3].sort.last
# [2, 1, 3].sort[-1]
# [2, 1, 3].sort.at(-1)
# [2, 1, 3].sort.slice(-1)
#
# # good
# [2, 1, 3].max
#
# # bad
# arr.sort_by(&:foo).first
# arr.sort_by(&:foo)[0]
# arr.sort_by(&:foo).at(0)
# arr.sort_by(&:foo).slice(0)
#
# # good
# arr.min_by(&:foo)
#
# # bad
# arr.sort_by(&:foo).last
# arr.sort_by(&:foo)[-1]
# arr.sort_by(&:foo).at(-1)
# arr.sort_by(&:foo).slice(-1)
#
# # good
# arr.max_by(&:foo)
#
class RedundantSort < Cop
include RangeHelp
MSG = 'Use `%<suggestion>s` instead of '\
'`%<sorter>s...%<accessor_source>s`.'
SORT_METHODS = %i[sort sort_by].freeze
def_node_matcher :redundant_sort?, <<~MATCHER
{
(send $(send _ $:sort ...) ${:last :first})
(send $(send _ $:sort ...) ${:[] :at :slice} {(int 0) (int -1)})
(send $(send _ $:sort_by _) ${:last :first})
(send $(send _ $:sort_by _) ${:[] :at :slice} {(int 0) (int -1)})
(send ({block numblock} $(send _ ${:sort_by :sort}) ...) ${:last :first})
(send
({block numblock} $(send _ ${:sort_by :sort}) ...)
${:[] :at :slice} {(int 0) (int -1)}
)
}
MATCHER
# rubocop:disable Metrics/AbcSize
def on_send(node)
return unless sort_method?(node)
if (sort_node, sorter, accessor = redundant_sort?(node.parent))
ancestor = node.parent
elsif (sort_node, sorter, accessor = redundant_sort?(node.parent&.parent))
ancestor = node.parent.parent
else
return
end
add_offense(ancestor,
location: offense_range(sort_node, ancestor),
message: message(ancestor,
sorter,
accessor))
end
# rubocop:enable Metrics/AbcSize
def autocorrect(node)
sort_node, sorter, accessor = redundant_sort?(node)
lambda do |corrector|
# Remove accessor, e.g. `first` or `[-1]`.
corrector.remove(
range_between(
accessor_start(node),
node.loc.expression.end_pos
)
)
# Replace "sort" or "sort_by" with the appropriate min/max method.
corrector.replace(
sort_node.loc.selector,
suggestion(sorter, accessor, arg_value(node))
)
end
end
private
def sort_method?(node)
SORT_METHODS.include?(node.method_name)
end
def offense_range(sort_node, ancestor)
range_between(sort_node.loc.selector.begin_pos, ancestor.loc.expression.end_pos)
end
def message(node, sorter, accessor)
accessor_source = range_between(
node.loc.selector.begin_pos,
node.loc.expression.end_pos
).source
format(MSG,
suggestion: suggestion(sorter,
accessor,
arg_value(node)),
sorter: sorter,
accessor_source: accessor_source)
end
def suggestion(sorter, accessor, arg)
base(accessor, arg) + suffix(sorter)
end
def base(accessor, arg)
if accessor == :first || arg&.zero?
'min'
elsif accessor == :last || arg == -1
'max'
end
end
def suffix(sorter)
case sorter
when :sort
''
when :sort_by
'_by'
end
end
def arg_node(node)
node.arguments.first
end
def arg_value(node)
arg_node(node).nil? ? nil : arg_node(node).node_parts.first
end
# This gets the start of the accessor whether it has a dot
# (e.g. `.first`) or doesn't (e.g. `[0]`)
def accessor_start(node)
if node.loc.dot
node.loc.dot.begin_pos
else
node.loc.selector.begin_pos
end
end
end
end
end
end