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redundant_merge.rb
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redundant_merge.rb
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# frozen_string_literal: true
module RuboCop
module Cop
module Performance
# Identifies places where `Hash#merge!` can be replaced by `Hash#[]=`.
# You can set the maximum number of key-value pairs to consider
# an offense with `MaxKeyValuePairs`.
#
# @safety
# This cop is unsafe because RuboCop cannot determine if the
# receiver of `merge!` is actually a hash or not.
#
# @example
# # bad
# hash.merge!(a: 1)
# hash.merge!({'key' => 'value'})
#
# # good
# hash[:a] = 1
# hash['key'] = 'value'
#
# @example MaxKeyValuePairs: 2 (default)
# # bad
# hash.merge!(a: 1, b: 2)
#
# # good
# hash[:a] = 1
# hash[:b] = 2
class RedundantMerge < Base
include Alignment
extend AutoCorrector
AREF_ASGN = '%<receiver>s[%<key>s] = %<value>s'
MSG = 'Use `%<prefer>s` instead of `%<current>s`.'
RESTRICT_ON_SEND = %i[merge!].freeze
WITH_MODIFIER_CORRECTION = <<~RUBY
%<keyword>s %<condition>s
%<leading_space>s%<indent>s%<body>s
%<leading_space>send
RUBY
def_node_matcher :redundant_merge_candidate, <<~PATTERN
(send $!nil? :merge! [(hash $...) !kwsplat_type?])
PATTERN
def_node_matcher :modifier_flow_control?, <<~PATTERN
[{if while until} modifier_form?]
PATTERN
def on_send(node)
each_redundant_merge(node) do |redundant_merge_node|
message = message(node)
add_offense(redundant_merge_node, message: message) do |corrector|
redundant_merge_candidate(node) do |receiver, pairs|
new_source = to_assignments(receiver, pairs).join("\n")
if node.parent && pairs.size > 1
correct_multiple_elements(corrector, node, node.parent, new_source)
else
correct_single_element(corrector, node, new_source)
end
end
end
end
end
private
def message(node)
redundant_merge_candidate(node) do |receiver, pairs|
assignments = to_assignments(receiver, pairs).join('; ')
format(MSG, prefer: assignments, current: node.source)
end
end
def each_redundant_merge(node)
redundant_merge_candidate(node) do |receiver, pairs|
next if non_redundant_merge?(node, receiver, pairs)
yield node
end
end
def non_redundant_merge?(node, receiver, pairs)
pairs.empty? ||
non_redundant_pairs?(receiver, pairs) ||
kwsplat_used?(pairs) ||
non_redundant_value_used?(receiver, node)
end
def non_redundant_pairs?(receiver, pairs)
(pairs.size > 1 && !receiver.pure?) || pairs.size > max_key_value_pairs
end
def kwsplat_used?(pairs)
pairs.any?(&:kwsplat_type?)
end
def non_redundant_value_used?(receiver, node)
node.value_used? && !EachWithObjectInspector.new(node, receiver).value_used?
end
def correct_multiple_elements(corrector, node, parent, new_source)
if modifier_flow_control?(parent)
new_source = rewrite_with_modifier(node, parent, new_source)
node = parent
else
padding = "\n#{leading_spaces(node)}"
new_source.gsub!("\n", padding)
end
corrector.replace(node, new_source)
end
def correct_single_element(corrector, node, new_source)
corrector.replace(node, new_source)
end
def to_assignments(receiver, pairs)
pairs.map do |pair|
key, value = *pair
key = key.sym_type? && pair.colon? ? ":#{key.source}" : key.source
format(AREF_ASGN, receiver: receiver.source, key: key, value: value.source)
end
end
def rewrite_with_modifier(node, parent, new_source)
# FIXME: `|| 2` can be removed when support is limited to RuboCop 1.44 or higher.
# https://github.com/rubocop/rubocop/commit/02d1e5b
indent = ' ' * (configured_indentation_width || 2)
padding = "\n#{indent + leading_spaces(node)}"
new_source.gsub!("\n", padding)
format(WITH_MODIFIER_CORRECTION, keyword: parent.loc.keyword.source,
condition: parent.condition.source,
leading_space: leading_spaces(node),
indent: indent,
body: new_source).chomp
end
def leading_spaces(node)
node.source_range.source_line[/\A\s*/]
end
def max_key_value_pairs
Integer(cop_config['MaxKeyValuePairs'] || 2)
end
# A utility class for checking the use of values within an
# `each_with_object` call.
class EachWithObjectInspector
extend NodePattern::Macros
def initialize(node, receiver)
@node = node
@receiver = unwind(receiver)
end
def value_used?
return false unless eligible_receiver? && second_argument
receiver.loc.name.source == second_argument.loc.name.source
end
private
attr_reader :node, :receiver
def eligible_receiver?
receiver.respond_to?(:lvar_type?) && receiver.lvar_type?
end
def second_argument
parent = node.parent
parent = parent.parent if parent.begin_type?
@second_argument ||= each_with_object_node(parent)
end
def unwind(receiver)
receiver, = *receiver while receiver.respond_to?(:send_type?) && receiver.send_type?
receiver
end
def_node_matcher :each_with_object_node, <<~PATTERN
(block (send _ :each_with_object _) (args _ $_) ...)
PATTERN
end
end
end
end
end