Class: RuboCop::Cop::Lint::UselessAssignment

Inherits:
Cop
  • Object
show all
Includes:
NameSimilarity
Defined in:
lib/rubocop/cop/lint/useless_assignment.rb

Overview

This cop checks for every useless assignment to local variable in every scope. The basic idea for this cop was from the warning of ‘ruby -cw`:

assigned but unused variable - foo

Currently this cop has advanced logic that detects unreferenced reassignments and properly handles varied cases such as branch, loop, rescue, ensure, etc.

Examples:


# bad

def some_method
  some_var = 1
  do_something
end

# good

def some_method
  some_var = 1
  do_something(some_var)
end

Constant Summary collapse

MSG = 
'Useless assignment to variable - `%s`.'.freeze

Constants included from NameSimilarity

NameSimilarity::MINIMUM_SIMILARITY_TO_SUGGEST

Constants included from Util

Util::ASGN_NODES, Util::BYTE_ORDER_MARK, Util::CONDITIONAL_NODES, Util::EQUALS_ASGN_NODES, Util::LITERAL_REGEX, Util::LOGICAL_OPERATOR_NODES, Util::MODIFIER_NODES, Util::OPERATOR_METHODS, Util::SHORTHAND_ASGN_NODES

Instance Attribute Summary

Attributes inherited from Cop

#config, #corrections, #offenses, #processed_source

Instance Method Summary collapse

Methods included from NameSimilarity

#find_similar_name

Methods inherited from Cop

#add_offense, all, badge, #config_to_allow_offenses, #config_to_allow_offenses=, #cop_config, #cop_name, cop_name, #correct, department, #duplicate_location?, #excluded_file?, #find_location, #highlights, inherited, #initialize, lint?, match?, #message, #messages, non_rails, #parse, qualified_cop_name, #relevant_file?, #target_ruby_version

Methods included from AST::Sexp

#s

Methods included from NodePattern::Macros

#def_node_matcher, #def_node_search, #node_search, #node_search_all, #node_search_body, #node_search_first

Methods included from AutocorrectLogic

#autocorrect?, #autocorrect_enabled?, #autocorrect_requested?, #support_autocorrect?

Methods included from IgnoredNode

#ignore_node, #ignored_node?, #part_of_ignored_node?

Methods included from Util

begins_its_line?, block_length, comment_line?, compatible_external_encoding_for?, directions, double_quotes_acceptable?, double_quotes_required?, effective_column, ends_its_line?, escape_string, first_part_of_call_chain, hard_to_type?, interpret_string_escapes, line_distance, line_range, move_pos, needs_escaping?, numeric_range_size, on_node, operator?, parentheses?, parenthesized_call?, preceed?, range_between, range_with_surrounding_comma, range_with_surrounding_space, same_line?, source_range, strip_quotes, stripped_source_upto, to_string_literal, to_supported_styles, to_symbol_literal, within_node?

Methods included from PathUtil

absolute?, match_path?, relative_path

Constructor Details

This class inherits a constructor from RuboCop::Cop::Cop

Instance Method Details

#after_leaving_scope(scope, _variable_table) ⇒ Object 



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 41

def after_leaving_scope(scope, _variable_table)
  scope.variables.each_value do |variable|
    check_for_unused_assignments(variable)
  end
end

#check_for_unused_assignments(variable) ⇒ Object 



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 47

def check_for_unused_assignments(variable)
  return if variable.should_be_unused?

  variable.assignments.each do |assignment|
    next if assignment.used?

    message = message_for_useless_assignment(assignment)

    location = if assignment.regexp_named_capture?
                 assignment.node.children.first.source_range
               else
                 assignment.node.loc.name
               end

    add_offense(nil, location, message)
  end
end

#collect_variable_like_names(scope) ⇒ Object 



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 111

def collect_variable_like_names(scope)
  names = scope.each_node.with_object(Set.new) do |node, set|
    if variable_like_method_invocation?(node)
      _receiver, method_name, = *node
      set << method_name
    end
  end

  variable_names = scope.variables.each_value.map(&:name)
  names.merge(variable_names)
end

#join_force?(force_class) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 37

def join_force?(force_class)
  force_class == VariableForce
end

#message_for_useless_assignment(assignment) ⇒ Object 



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 65

def message_for_useless_assignment(assignment)
  variable = assignment.variable

  format(MSG, variable.name) +
    message_specification(assignment, variable).to_s
end

#message_specification(assignment, variable) ⇒ Object 



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 72

def message_specification(assignment, variable)
  if assignment.multiple_assignment?
    multiple_assignment_message(variable.name)
  elsif assignment.operator_assignment?
    operator_assignment_message(variable.scope, assignment)
  else
    similar_name_message(variable)
  end
end

#multiple_assignment_message(variable_name) ⇒ Object 



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 82

def multiple_assignment_message(variable_name)
  " Use `_` or `_#{variable_name}` as a variable name to indicate " \
    "that it won't be used."
end

#operator_assignment_message(scope, assignment) ⇒ Object 



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 87

def operator_assignment_message(scope, assignment)
  return_value_node = return_value_node_of_scope(scope)
  return unless assignment.meta_assignment_node
                          .equal?(return_value_node)

  " Use just operator `#{assignment.operator.sub(/=$/, '')}`."
end

#return_value_node_of_scope(scope) ⇒ Object

TODO: More precise handling (rescue, ensure, nested begin, etc.)



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 101

def return_value_node_of_scope(scope)
  body_node = scope.body_node

  if body_node.begin_type?
    body_node.children.last
  else
    body_node
  end
end

#similar_name_message(variable) ⇒ Object 



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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 95

def similar_name_message(variable)
  similar_name = find_similar_name(variable.name, variable.scope)
  " Did you mean `#{similar_name}`?" if similar_name
end

#variable_like_method_invocation?(node) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/rubocop/cop/lint/useless_assignment.rb', line 123

def variable_like_method_invocation?(node)
  return false unless node.send_type?
  receiver, _method_name, *args = *node
  receiver.nil? && args.empty?
end