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redundant_begin.rb
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redundant_begin.rb
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# frozen_string_literal: true
module RuboCop
module Cop
module Style
# Checks for redundant `begin` blocks.
#
# Currently it checks for code like this:
#
# @example
#
# # bad
# def redundant
# begin
# ala
# bala
# rescue StandardError => e
# something
# end
# end
#
# # good
# def preferred
# ala
# bala
# rescue StandardError => e
# something
# end
#
# # bad
# begin
# do_something
# end
#
# # good
# do_something
#
# # bad
# # When using Ruby 2.5 or later.
# do_something do
# begin
# something
# rescue => ex
# anything
# end
# end
#
# # good
# # In Ruby 2.5 or later, you can omit `begin` in `do-end` block.
# do_something do
# something
# rescue => ex
# anything
# end
#
# # good
# # Stabby lambdas don't support implicit `begin` in `do-end` blocks.
# -> do
# begin
# foo
# rescue Bar
# baz
# end
# end
class RedundantBegin < Base
include RangeHelp
extend AutoCorrector
MSG = 'Redundant `begin` block detected.'
# @!method offensive_kwbegins(node)
def_node_search :offensive_kwbegins, <<~PATTERN
[(kwbegin ...) !#allowable_kwbegin?]
PATTERN
def on_def(node)
return unless node.body&.kwbegin_type?
register_offense(node.body)
end
alias on_defs on_def
def on_block(node)
return if node.send_node.lambda_literal?
return if node.braces?
return unless node.body&.kwbegin_type?
register_offense(node.body)
end
def on_kwbegin(node)
return unless (target_node = offensive_kwbegins(node).to_a.last)
register_offense(target_node)
end
private
def allowable_kwbegin?(node)
empty_begin?(node) ||
begin_block_has_multiline_statements?(node) ||
contain_rescue_or_ensure?(node) ||
valid_context_using_only_begin?(node)
end
def register_offense(node)
offense_range = node.loc.begin
add_offense(offense_range) do |corrector|
if node.parent&.assignment?
replace_begin_with_statement(corrector, offense_range, node)
else
corrector.remove(offense_range)
end
if use_modifier_form_after_multiline_begin_block?(node)
correct_modifier_form_after_multiline_begin_block(corrector, node)
end
corrector.remove(node.loc.end)
end
end
def replace_begin_with_statement(corrector, offense_range, node)
first_child = node.children.first
source = first_child.source
source = "(#{source})" if first_child.if_type? && first_child.modifier_form?
corrector.replace(offense_range, source)
corrector.remove(range_between(offense_range.end_pos, first_child.source_range.end_pos))
restore_removed_comments(corrector, offense_range, node, first_child)
end
# Restore comments that occur between "begin" and "first_child".
# These comments will be moved to above the assignment line.
def restore_removed_comments(corrector, offense_range, node, first_child)
comments_range = range_between(offense_range.end_pos, first_child.source_range.begin_pos)
comments = comments_range.source
corrector.insert_before(node.parent, comments) unless comments.blank?
end
def use_modifier_form_after_multiline_begin_block?(node)
return unless (parent = node.parent)
node.multiline? && parent.if_type? && parent.modifier_form?
end
def correct_modifier_form_after_multiline_begin_block(corrector, node)
condition_range = condition_range(node.parent)
corrector.insert_after(node.children.first, " #{condition_range.source}")
corrector.remove(range_by_whole_lines(condition_range, include_final_newline: true))
end
def condition_range(node)
range_between(node.loc.keyword.begin_pos, node.condition.source_range.end_pos)
end
def empty_begin?(node)
node.children.empty?
end
def begin_block_has_multiline_statements?(node)
node.children.count >= 2
end
def contain_rescue_or_ensure?(node)
first_child = node.children.first
first_child.rescue_type? || first_child.ensure_type?
end
def valid_context_using_only_begin?(node)
parent = node.parent
valid_begin_assignment?(node) || parent&.post_condition_loop? ||
parent&.send_type? || parent&.operator_keyword?
end
def valid_begin_assignment?(node)
node.parent&.assignment? && !node.children.one?
end
end
end
end
end