[Fix #9061] Add new Lint/IncompatibleIoSelectWithFiberScheduler cop

Fixes #9061.

This PR adds new `Lint/IncompatibleIoSelectWithFiberScheduler` cop.
It checks for `IO.select` that is incompatible with Fiber Scheduler since Ruby 3.0.

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

# good
io.wait_readable(timeout)

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

# good
io.wait_writable(timeout)
```

Ref: `Fiber Scheduler` section of https://www.ruby-lang.org/en/news/2020/12/25/ruby-3-0-0-released/

This PR will make it possible to detect proven cases with redis/redis-rb#960.

changelog/new_add_new_incompatible_io_select_with_fiber_scheduler_cop.md

@@ -0,0 +1 @@
+* [#9061](https://github.com/rubocop/rubocop/issues/9061): Add new `Lint/IncompatibleIoSelectWithFiberScheduler` cop. ([@koic][])

config/default.yml

@@ -1777,6 +1777,11 @@ Lint/ImplicitStringConcatenation:
   Enabled: true
   VersionAdded: '0.36'
 
+Lint/IncompatibleIoSelectWithFiberScheduler:
+  Description: 'Checks for `IO.select` that is incompatible with Fiber Scheduler.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Lint/IneffectiveAccessModifier:
   Description: >-
                  Checks for attempts to use `private` or `protected` to set

lib/rubocop.rb

@@ -307,8 +307,9 @@
 require_relative 'rubocop/cop/lint/heredoc_method_call_position'
 require_relative 'rubocop/cop/lint/identity_comparison'
 require_relative 'rubocop/cop/lint/implicit_string_concatenation'
-require_relative 'rubocop/cop/lint/inherit_exception'
+require_relative 'rubocop/cop/lint/incompatible_io_select_with_fiber_scheduler'
 require_relative 'rubocop/cop/lint/ineffective_access_modifier'
+require_relative 'rubocop/cop/lint/inherit_exception'
 require_relative 'rubocop/cop/lint/interpolation_check'
 require_relative 'rubocop/cop/lint/lambda_without_literal_block'
 require_relative 'rubocop/cop/lint/literal_as_condition'

lib/rubocop/cop/lint/incompatible_io_select_with_fiber_scheduler.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      #
+      # This cop checks for `IO.select` that is incompatible with Fiber Scheduler since Ruby 3.0.
+      #
+      # @example
+      #
+      #   # bad
+      #   IO.select([io], [], [], timeout)
+      #
+      #   # good
+      #   io.wait_readable(timeout)
+      #
+      #   # bad
+      #   IO.select([], [io], [], timeout)
+      #
+      #   # good
+      #   io.wait_writable(timeout)
+      #
+      class IncompatibleIoSelectWithFiberScheduler < Base
+        extend AutoCorrector
+
+        MSG = 'Use `%<preferred>s` instead of `%<current>s`.'
+        RESTRICT_ON_SEND = %i[select].freeze
+
+        # @!method io_select(node)
+        def_node_matcher :io_select, <<~PATTERN
+          (send
+            (const {nil? cbase} :IO) :select $_ $_ {(array) nil} $...)
+        PATTERN
+
+        def on_send(node)
+          return unless (read, write, timeout = io_select(node))
+          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|
+            corrector.replace(node, preferred)
+          end
+        end
+
+        private
+
+        def scheduler_compatible?(io1, io2)
+          return false unless io1.array_type? && io1.values.size == 1
+
+          io2.array_type? ? io2.values.empty? : io2.nil_type?
+        end
+
+        def preferred_method(read, write, timeout)
+          timeout_argument = timeout.empty? ? '' : "(#{timeout[0].source})"
+
+          if read.array_type? && read.values[0]
+            "#{read.values[0].source}.wait_readable#{timeout_argument}"
+          else
+            "#{write.values[0].source}.wait_writable#{timeout_argument}"
+          end
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/incompatible_io_select_with_fiber_scheduler_spec.rb

@@ -0,0 +1,131 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::IncompatibleIoSelectWithFiberScheduler, :config do
+  it 'registers and corrects an offense when using `IO.select` with single read argument' do
+    expect_offense(<<~RUBY)
+      IO.select([io], [], [])
+      ^^^^^^^^^^^^^^^^^^^^^^^ Use `io.wait_readable` instead of `IO.select([io], [], [])`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      io.wait_readable
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `IO.select` with single read and timeout arguments' do
+    expect_offense(<<~RUBY)
+      IO.select([io], [], [], timeout)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `io.wait_readable(timeout)` instead of `IO.select([io], [], [], timeout)`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      io.wait_readable(timeout)
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `::IO.select` with single read argument' do
+    expect_offense(<<~RUBY)
+      ::IO.select([io], [], [])
+      ^^^^^^^^^^^^^^^^^^^^^^^^^ Use `io.wait_readable` instead of `::IO.select([io], [], [])`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      io.wait_readable
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `::IO.select` with single read and timeout arguments' do
+    expect_offense(<<~RUBY)
+      ::IO.select([io], [], [], timeout)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `io.wait_readable(timeout)` instead of `::IO.select([io], [], [], timeout)`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      io.wait_readable(timeout)
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `IO.select` with single read, `nil`, and timeout arguments' do
+    expect_offense(<<~RUBY)
+      IO.select([io], nil, nil, timeout)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `io.wait_readable(timeout)` instead of `IO.select([io], nil, nil, timeout)`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      io.wait_readable(timeout)
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `IO.select` with single write, `nil`, and timeout arguments' do
+    expect_offense(<<~RUBY)
+      IO.select(nil, [io], nil, timeout)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `io.wait_writable(timeout)` instead of `IO.select(nil, [io], nil, timeout)`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      io.wait_writable(timeout)
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `IO.select` with single write argument' do
+    expect_offense(<<~RUBY)
+      IO.select([], [io], [])
+      ^^^^^^^^^^^^^^^^^^^^^^^ Use `io.wait_writable` instead of `IO.select([], [io], [])`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      io.wait_writable
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `IO.select` with single write and timeout arguments' do
+    expect_offense(<<~RUBY)
+      IO.select([], [io], [], timeout)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `io.wait_writable(timeout)` instead of `IO.select([], [io], [], timeout)`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      io.wait_writable(timeout)
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `IO.select` with single read as `self` and timeout arguments' do
+    expect_offense(<<~RUBY)
+      IO.select([self], nil, nil, timeout)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `self.wait_readable(timeout)` instead of `IO.select([self], nil, nil, timeout)`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      self.wait_readable(timeout)
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `IO.select` with single write as `self` and timeout arguments' do
+    expect_offense(<<~RUBY)
+      IO.select(nil, [self], nil, timeout)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `self.wait_writable(timeout)` instead of `IO.select(nil, [self], nil, timeout)`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      self.wait_writable(timeout)
+    RUBY
+  end
+
+  it 'does not register an offense when using `IO.select` with multiple read arguments' do
+    expect_no_offenses(<<~RUBY)
+      IO.select([foo, bar], [], [])
+    RUBY
+  end
+
+  it 'does not register an offense when using `IO.select` with multiple write arguments' do
+    expect_no_offenses(<<~RUBY)
+      IO.select([], [foo, bar], [])
+    RUBY
+  end
+
+  it 'does not register an offense when using `IO.select` with read and write arguments' do
+    expect_no_offenses(<<~RUBY)
+      IO.select([rp], [wp], [])
+    RUBY
+  end
+end