Class: RuboCop::Cop::Style::FetchEnvVar

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/fetch_env_var.rb


Suggests ENV.fetch for the replacement of ENV[]. ENV[] silently fails and returns nil when the environment variable is unset, which may cause unexpected behaviors when the developer forgets to set it. On the other hand, ENV.fetch raises KeyError or returns the explicitly specified default value.


# bad
x = ENV['X']

# good
x = ENV.fetch('X')

# also good
ENV['X'].some_method # (e.g. `.nil?`)

Constant Summary

::RuboCop::Cop::Base - Inherited


Class Attribute Summary

::RuboCop::Cop::AutoCorrector - Extended

::RuboCop::Cop::Base - Inherited

.gem_requirements, .lint?,

Returns if class supports autocorrect.


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


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



.callbacks_needed, .cop_name, .department,

Returns an url to view this cops documentation online.


Call for abstract Cop classes.


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


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


Register a version requirement for the given gem name.


::RuboCop::ExcludeLimit - Extended


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


Instance Attribute Summary

Instance Method Summary

::RuboCop::Cop::Base - Inherited


Adds an offense that has no particular location.


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.


Called before any investigation.


Configuration Helpers.

#cop_name, #excluded_file?,

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


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.


Alias for Base#cop_name.


Called after all on_…​


Called before all on_…​


Called instead of all on_…​


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


Called between investigations.

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

Reserved for Cop::Cop.


Called to complete an investigation.

#correct, #current_corrector,

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,

Actually private methods.


::RuboCop::Cop::AutocorrectLogic - Included

::RuboCop::Cop::IgnoredNode - Included

Constructor Details

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

Instance Method Details

#allowable_use?(node) ⇒ Boolean (private)

The following are allowed cases:

  • Used as a flag (e.g., if ENV['X'] or !ENV['X']) because it simply checks whether the variable is set.

  • Receiving a message with dot syntax, e.g. ENV['X'].nil?.

  • ENV['key'] assigned by logical AND/OR assignment.

  • ENV['key'] is the LHS of a ||.

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 105

def allowable_use?(node)
  used_as_flag?(node) || message_chained_with_dot?(node) || assigned?(node) || or_lhs?(node)

#allowed_var?(node) ⇒ Boolean (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 48

def allowed_var?(node)
  env_key_node = node.children.last
  env_key_node.str_type? && cop_config['AllowedVars'].include?(env_key_node.value)

#assigned?(node) ⇒ Boolean (private)

The following are allowed cases:

  • ENV['key'] is a receiver of ||=, e.g. ENV['X'] ||= y.

  • ENV['key'] is a receiver of &&=, e.g. ENV['X'] &&= y.

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 113

def assigned?(node)
  return false unless (parent = node.parent)&.assignment?

  lhs, _method, _rhs = *parent
  node == lhs


[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 31

def_node_matcher :env_with_bracket?, <<~PATTERN
  (send (const nil? :ENV) :[] $_)

#message_chained_with_dot?(node) ⇒ Boolean (private)

Check if the node is a receiver and receives a message with dot syntax.

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 89

def message_chained_with_dot?(node)
  return false if node.root?

  parent = node.parent
  return false if !parent.call_type? || parent.children.first != node

  parent.dot? || parent.safe_navigation?

#new_code(name_node) (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 126

def new_code(name_node)
  "ENV.fetch(#{name_node.source}, nil)"

#offensive?(node) ⇒ Boolean (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 84

def offensive?(node)
  !(allowed_var?(node) || allowable_use?(node))


[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 35

def on_send(node)
  env_with_bracket?(node) do |name_node|
    break unless offensive?(node)

    message = format(MSG, key: name_node.source)
    add_offense(node, message: message) do |corrector|
      corrector.replace(node, new_code(name_node))

#or_lhs?(node) ⇒ Boolean (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 120

def or_lhs?(node)
  return false unless (parent = node.parent)&.or_type?

  parent.lhs == node || parent.parent&.or_type?

#partial_matched?(node, condition) ⇒ Boolean (private)

Avoid offending in the following cases: ENV['key'] if ENV['key'] = x

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 80

def partial_matched?(node, condition)
  node.child_nodes == node.child_nodes & condition.child_nodes

#used_as_flag?(node) ⇒ Boolean (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 53

def used_as_flag?(node)
  return false if node.root?
  return true if used_if_condition_in_body(node)

  node.parent.send_type? && (node.parent.prefix_bang? || node.parent.comparison_method?)

#used_if_condition_in_body(node) (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/fetch_env_var.rb', line 60

def used_if_condition_in_body(node)
  if_node = node.ancestors.find(&:if_type?)

  return false unless (condition = if_node&.condition)
  return true if condition.send_type? && (condition.child_nodes == node.child_nodes)

  used_in_condition?(node, condition)

#used_in_condition?(node, condition) ⇒ Boolean (private)

[ GitHub ]

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

def used_in_condition?(node, condition)
  if condition.send_type?
    return true if condition.assignment_method? && partial_matched?(node, condition)
    return false if !condition.comparison_method? && !condition.predicate_method?