Merge pull request #36 from viralpraxis/add-dir-chdir-cop

Add `ThreadSafety::DirChdir` cop

config/default.yml

@@ -30,3 +30,7 @@ ThreadSafety/NewThread:
                  Avoid starting new threads.
                  Let a framework like Sidekiq handle the threads.
   Enabled: true
+
+ThreadSafety/DirChdir:
+  Description: Avoid using `Dir.chdir` due to its process-wide effect.
+  Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -4,3 +4,4 @@
 * xref:cops_threadsafety.adoc#threadsafetyinstancevariableinclassmethod[ThreadSafety/InstanceVariableInClassMethod]
 * xref:cops_threadsafety.adoc#threadsafetymutableclassinstancevariable[ThreadSafety/MutableClassInstanceVariable]
 * xref:cops_threadsafety.adoc#threadsafetynewthread[ThreadSafety/NewThread]
+* xref:cops_threadsafety.adoc#threadsafetydirchdir[ThreadSafety/DirChdir]

docs/modules/ROOT/pages/cops_threadsafety.adoc

@@ -32,6 +32,28 @@ class User
 end
 ----
 
+== ThreadSafety/DirChdir
+
+|===
+| Enabled by default | Safe | Supports autocorrection | Version Added | Version Changed
+
+| Enabled
+| Yes
+| No
+| -
+| -
+|===
+
+Avoid using `Dir.chdir` due to its process-wide effect.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+Dir.chdir("/var/run")
+----
+
 == ThreadSafety/InstanceVariableInClassMethod
 
 |===

lib/rubocop-thread_safety.rb

@@ -12,3 +12,4 @@
 require 'rubocop/cop/thread_safety/class_and_module_attributes'
 require 'rubocop/cop/thread_safety/mutable_class_instance_variable'
 require 'rubocop/cop/thread_safety/new_thread'
+require 'rubocop/cop/thread_safety/dir_chdir'

lib/rubocop/cop/thread_safety/dir_chdir.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module ThreadSafety
+      # Avoid using `Dir.chdir` due to its process-wide effect.
+      #
+      # @example
+      #   # bad
+      #   Dir.chdir("/var/run")
+      class DirChdir < Base
+        MSG = 'Avoid using `Dir.chdir` due to its process-wide effect.'
+        RESTRICT_ON_SEND = %i[chdir].freeze
+
+        # @!method dir_chdir?(node)
+        def_node_matcher :dir_chdir?, <<~MATCHER
+          (send (const {nil? cbase} :Dir) :chdir ...)
+        MATCHER
+
+        def on_send(node)
+          dir_chdir?(node) { add_offense(node) }
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/thread_safety/dir_chdir_spec.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::ThreadSafety::DirChdir, :config do
+  let(:msg) { 'Avoid using `Dir.chdir` due to its process-wide effect.' }
+
+  context 'with `Dir.chdir` method' do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        Dir.chdir("/var/run")
+        ^^^^^^^^^^^^^^^^^^^^^ #{msg}
+      RUBY
+    end
+
+    it 'registers an offense when called without arguments' do
+      expect_offense(<<~RUBY)
+        Dir.chdir
+        ^^^^^^^^^ #{msg}
+      RUBY
+    end
+
+    it 'registers an offense with top-level constant' do
+      expect_offense(<<~RUBY)
+        ::Dir.chdir("/var/run")
+        ^^^^^^^^^^^^^^^^^^^^^^^ #{msg}
+      RUBY
+    end
+  end
+
+  context 'with another `Dir` class method' do
+    it 'does not register an offense' do
+      expect_no_offenses 'Dir.pwd'
+    end
+  end
+
+  context 'when received is not `Dir`' do
+    it 'does not register an offense' do
+      expect_no_offenses 'chdir("/tmp")'
+    end
+  end
+end