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Class: RuboCop::Cop::Style::StringConcatenation

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::RuboCop::Cop::AutoCorrector, ::RuboCop::Cop::Base, ::RuboCop::ExcludeLimit, NodePattern::Macros, RuboCop::AST::Sexp
Instance Chain:
Inherits: RuboCop::Cop::Base
Defined in: lib/rubocop/cop/style/string_concatenation.rb

Overview

Checks for places where string concatenation can be replaced with string interpolation.

The cop can autocorrect simple cases but will skip autocorrecting more complex cases where the resulting code would be harder to read. In those cases, it might be useful to extract statements to local variables or methods which you can then interpolate in a string.

Note
When concatenation between two strings is broken over multiple lines, this cop does not register an offense; instead, Style/LineEndConcatenation will pick up the offense if enabled.

Two modes are supported: 1. aggressive style checks and corrects all occurrences of ` where either the left or right side of ` is a string literal. 2. conservative style on the other hand, checks and corrects only if left side (receiver of + method call) is a string literal. This is useful when the receiver is some expression that returns string like Pathname instead of a string literal.

Examples:

Mode: aggressive (default)

# bad
email_with_name = user.name + ' <' + user.email + '>'
Pathname.new('/') + 'test'

# good
email_with_name = "#{user.name} <#{user.email}>"
email_with_name = format('%s <%s>', user.name, user.email)
"#{Pathname.new('/')}test"

# accepted, line-end concatenation
name = 'First' +
  'Last'

Mode: conservative

# bad
'Hello' + user.name

# good
"Hello #{user.name}"
user.name + '!!'
Pathname.new('/') + 'test'

Cop Safety Information:

  • This cop is unsafe in aggressive mode, as it cannot be guaranteed that the receiver is actually a string, which can result in a false positive.

Constant Summary

::RuboCop::Cop::Base - Inherited

EMPTY_OFFENSES, RESTRICT_ON_SEND

::RuboCop::PathUtil - Included

HIDDEN_FILE_PATTERN, SMART_PATH_CACHE

::RuboCop::Cop::Util - Included

LINE_BEGINS_REGEX_CACHE, LITERAL_REGEX, MAX_LINE_BEGINS_REGEX_INDEX

::RuboCop::Cop::RangeHelp - Included

BYTE_ORDER_MARK, NOT_GIVEN

Class Attribute Summary

::RuboCop::Cop::AutoCorrector - Extended

::RuboCop::Cop::Base - Inherited

.gem_requirements, .lint?,
.support_autocorrect?

Returns if class supports autocorrect.

.support_multiple_source?

Override if your cop should be called repeatedly for multiple investigations Between calls to on_new_investigation and on_investigation_end, the result of processed_source will remain constant.

Class Method Summary

::RuboCop::Cop::Base - Inherited

.autocorrect_incompatible_with

List of cops that should not try to autocorrect at the same time as this cop.

.badge

Naming.

.callbacks_needed, .cop_name, .department,
.documentation_url

Returns an url to view this cops documentation online.

.exclude_from_registry

Call for abstract Cop classes.

.inherited,
.joining_forces

Override and return the Force class(es) you need to join.

.match?

Returns true if the cop name or the cop namespace matches any of the given names.

.new,
.requires_gem

Register a version requirement for the given gem name.

.restrict_on_send

::RuboCop::ExcludeLimit - Extended

exclude_limit

Sets up a configuration option to have an exclude limit tracked.

transform

Instance Attribute Summary

Instance Method Summary

::RuboCop::Cop::RangeHelp - Included

#add_range, #column_offset_between,
#contents_range

A range containing only the contents of a literal with delimiters (e.g.

#directions,
#effective_column

Returns the column attribute of the range, except if the range is on the first line and there’s a byte order mark at the beginning of that line, in which case 1 is subtracted from the column value.

#final_pos, #move_pos, #move_pos_str, #range_between, #range_by_whole_lines, #range_with_comments, #range_with_comments_and_lines, #range_with_surrounding_comma, #range_with_surrounding_space, #source_range

::RuboCop::Cop::Util - Included

#add_parentheses

Metrics/MethodLength.

#any_descendant?

Metrics/MethodLength.

#args_begin, #args_end, #begins_its_line?,
#comment_line?

This is a bad API.

#comment_lines?, #compatible_external_encoding_for?,
#double_quotes_required?

If converting a string to Ruby string literal source code, must double quotes be used?

#escape_string,
#first_part_of_call_chain

Returns, for example, a bare if node if the given node is an if with calls chained to the end of it.

#include_or_equal?, #indent, #interpret_string_escapes, #line, #line_range, #needs_escaping?, #on_node, #parentheses?, #same_line?, #to_string_literal, #to_supported_styles, #trim_string_interpolation_escape_character

::RuboCop::PathUtil - Included

#absolute?

Returns true for an absolute Unix or Windows path.

#glob?

Returns true for a glob.

#hidden_dir?, #hidden_file?, #hidden_file_in_not_hidden_dir?,
#match_path?

Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity.

#maybe_hidden_file?

Loose check to reduce memory allocations.

#relative_path, #smart_path

::RuboCop::Cop::Base - Inherited

#add_global_offense

Adds an offense that has no particular location.

#add_offense

Adds an offense on the specified range (or node with an expression) Unless that offense is disabled for this range, a corrector will be yielded to provide the cop the opportunity to autocorrect the offense.

#begin_investigation

Called before any investigation.

#callbacks_needed,
#cop_config

Configuration Helpers.

#cop_name, #excluded_file?,
#external_dependency_checksum

This method should be overridden when a cop’s behavior depends on state that lives outside of these locations:

#inspect
#message

Gets called if no message is specified when calling add_offense or add_global_offense Cops are discouraged to override this; instead pass your message directly.

#name

Alias for Base#cop_name.

#offenses,
#on_investigation_end

Called after all on_…​

#on_new_investigation

Called before all on_…​

#on_other_file

Called instead of all on_…​

#parse

There should be very limited reasons for a Cop to do it’s own parsing.

#parser_engine,
#ready

Called between investigations.

#relevant_file?, #target_rails_version, #target_ruby_version, #annotate, #apply_correction, #attempt_correction,
#callback_argument

Reserved for Cop::Cop.

#complete_investigation

Called to complete an investigation.

#correct, #current_corrector,
#current_offense_locations

Reserved for Commissioner:

#current_offenses, #currently_disabled_lines, #custom_severity, #default_severity, #disable_uncorrectable, #enabled_line?, #file_name_matches_any?, #find_message, #find_severity, #range_for_original, #range_from_node_or_range,
#reset_investigation

Actually private methods.

#use_corrector

::RuboCop::Cop::AutocorrectLogic - Included

::RuboCop::Cop::IgnoredNode - Included

Constructor Details

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

Instance Method Details

#collect_parts(node, parts = []) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 116

def collect_parts(node, parts = [])
  return unless node

  if plus_node?(node)
    collect_parts(node.receiver, parts)
    collect_parts(node.first_argument, parts)
  else
    parts << node
  end
end

#corrected_ancestor?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 141

def corrected_ancestor?(node)
  node.each_ancestor(:send).any? { |ancestor| @corrected_nodes&.include?(ancestor) }
end

#find_topmost_plus_node(node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 108

def find_topmost_plus_node(node)
  current = node
  while (parent = current.parent) && plus_node?(parent)
    current = parent
  end
  current
end

#handle_quotes(parts) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 162

def handle_quotes(parts)
  parts.map do |part|
    part == '"' ? '\"' : part
  end
end

#heredoc?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 135

def heredoc?(node)
  return false unless node.str_type? || node.dstr_type?

  node.heredoc?
end

#line_end_concatenation?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 98

def line_end_concatenation?(node)
  # If the concatenation happens at the end of the line,
  # and both the receiver and argument are strings, allow
  # `Style/LineEndConcatenation` to handle it instead.
  node.receiver.str_type? &&
    node.first_argument.str_type? &&
    node.multiline? &&
    node.source =~ /\+\s*\n/
end

#mode (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 172

def mode
  cop_config['Mode'].to_sym
end

#on_new_investigation

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 69

def on_new_investigation
  @corrected_nodes = nil
end

#on_send(node)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 73

def on_send(node)
  return unless string_concatenation?(node)
  return if line_end_concatenation?(node)

  topmost_plus_node = find_topmost_plus_node(node)
  parts = collect_parts(topmost_plus_node)
  return if mode == :conservative && !parts.first.str_type?

  register_offense(topmost_plus_node, parts)
end

#plus_node?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 127

def plus_node?(node)
  node.send_type? && node.method?(:+)
end

#register_offense(topmost_plus_node, parts) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 86

def register_offense(topmost_plus_node, parts)
  add_offense(topmost_plus_node) do |corrector|
    correctable_parts = parts.none? { |part| uncorrectable?(part) }
    if correctable_parts && !corrected_ancestor?(topmost_plus_node)
      corrector.replace(topmost_plus_node, replacement(parts))

      @corrected_nodes ||= Set.new.compare_by_identity
      @corrected_nodes.add(topmost_plus_node)
    end
  end
end

#replacement(parts) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 145

def replacement(parts)
  interpolated_parts =
    parts.map do |part|
      case part.type
      when :str
        value = part.value
        single_quoted?(part) ? value.gsub(/(\\|")/, '\\\\\&') : value.inspect[1..-2]
      when :dstr
        contents_range(part).source
      else
        "\#{#{part.source}}"
      end
    end

  "\"#{handle_quotes(interpolated_parts).join}\""
end

#single_quoted?(str_node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 168

def single_quoted?(str_node)
  str_node.source.start_with?("'")
end

#string_concatenation?(node)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 62

def_node_matcher :string_concatenation?, <<~PATTERN
  {
    (send str_type? :+ _)
    (send _ :+ str_type?)
  }
PATTERN

#uncorrectable?(part) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/string_concatenation.rb', line 131

def uncorrectable?(part)
  part.multiline? || heredoc?(part) || part.each_descendant(:block).any?
end