Class: RuboCop::Cop::Lint::IncompatibleIoSelectWithFiberScheduler

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/lint/incompatible_io_select_with_fiber_scheduler.rb


Checks for IO.select that is incompatible with Fiber Scheduler since Ruby 3.0.

When an array of IO objects waiting for an exception (the third argument of IO.select) is used as an argument, there is no alternative API, so offenses are not registered.

When the method is successful the return value of IO.select is , and the return value of io.wait_readable and io.wait_writable are self. They are not autocorrected when assigning a return value because these types are different. It’s up to user how to handle the return value.


# bad
IO.select([io], [], [], timeout)

# good

# bad
IO.select([], [io], [], timeout)

# good

Cop Safety Information:

  • This cop’s autocorrection is unsafe because NoMethodError occurs if require 'io/wait' is not called.

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


[ GitHub ]

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

def_node_matcher :io_select, <<~PATTERN
    (const {nil? cbase} :IO) :select $...)


[ GitHub ]

# File 'lib/rubocop/cop/lint/incompatible_io_select_with_fiber_scheduler.rb', line 46

def on_send(node)
  read, write, excepts, timeout = *io_select(node)
  return if excepts && !excepts.children.empty?
  return unless scheduler_compatible?(read, write) || scheduler_compatible?(write, read)

  preferred = preferred_method(read, write, timeout)
  message = format(MSG, preferred: preferred, current: node.source)

  add_offense(node, message: message) do |corrector|
    next if node.parent&.assignment?

    corrector.replace(node, preferred)

#preferred_method(read, write, timeout) (private)

[ GitHub ]

# File 'lib/rubocop/cop/lint/incompatible_io_select_with_fiber_scheduler.rb', line 69

def preferred_method(read, write, timeout)
  timeout_argument = timeout.nil? ? '' : "(#{timeout.source})"

  if read.array_type? && read.values[0]

#scheduler_compatible?(io1, io2) ⇒ Boolean (private)

[ GitHub ]

# File 'lib/rubocop/cop/lint/incompatible_io_select_with_fiber_scheduler.rb', line 63

def scheduler_compatible?(io1, io2)
  return false unless io1&.array_type? && io1.values.size == 1

  io2&.array_type? ? io2.values.empty? : (io2.nil? || io2.nil_type?)