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# frozen_string_literal: true
module RuboCop
module Cop
module Performance
# This cop is used to identify usages of
#
# @example
# # bad
# [1, 2, 3, 4].map { |e| [e, e] }.flatten(1)
# [1, 2, 3, 4].collect { |e| [e, e] }.flatten(1)
#
# # good
# [1, 2, 3, 4].flat_map { |e| [e, e] }
# [1, 2, 3, 4].map { |e| [e, e] }.flatten
# [1, 2, 3, 4].collect { |e| [e, e] }.flatten
class FlatMap < Cop
include RangeHelp
MSG = 'Use `flat_map` instead of `%<method>s...%<flatten>s`.'
FLATTEN_MULTIPLE_LEVELS = ' Beware, `flat_map` only flattens 1 level ' \
'and `flatten` can be used to flatten ' \
'multiple levels.'
def_node_matcher :flat_map_candidate?, <<~PATTERN
(send
{
(block $(send _ ${:collect :map}) ...)
$(send _ ${:collect :map} (block_pass _))
}
${:flatten :flatten!}
$...
)
PATTERN
def on_send(node)
flat_map_candidate?(node) do |map_node, first_method, flatten, params|
flatten_level, = *params.first
if cop_config['EnabledForFlattenWithoutParams'] && !flatten_level
offense_for_levels(node, map_node, first_method, flatten)
elsif flatten_level == 1
offense_for_method(node, map_node, first_method, flatten)
end
end
end
def autocorrect(node)
map_node, _first_method, _flatten, params = flat_map_candidate?(node)
flatten_level, = *params.first
return unless flatten_level
range = range_between(node.loc.dot.begin_pos,
node.source_range.end_pos)
lambda do |corrector|
corrector.remove(range)
corrector.replace(map_node.loc.selector, 'flat_map')
end
end
private
def offense_for_levels(node, map_node, first_method, flatten)
message = MSG + FLATTEN_MULTIPLE_LEVELS
register_offense(node, map_node, first_method, flatten, message)
end
def offense_for_method(node, map_node, first_method, flatten)
register_offense(node, map_node, first_method, flatten, MSG)
end
def register_offense(node, map_node, first_method, flatten, message)
range = range_between(map_node.loc.selector.begin_pos,
node.loc.expression.end_pos)
add_offense(node,
location: range,
message: format(message, method: first_method,
flatten: flatten))
end
end
end
end
end
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