Blacklist the use of "destroy_all"

This method usually has really bad performance implications, as it loads
rows into memory and deletes them one by one.

3 files changed, 66 insertions, 0 deletions

diff --git a/rubocop/cop/destroy_all.rb b/rubocop/cop/destroy_all.rb
new file mode 100644
index 00000000000..38b6cb40f91
--- /dev/null
+++ b/rubocop/cop/destroy_all.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    # Cop that blacklists the use of `destroy_all`.
+    class DestroyAll < RuboCop::Cop::Cop
+      MSG = 'Use `delete_all` instead of `destroy_all`. ' \
+        '`destroy_all` will load the rows into memory, then execute a ' \
+        '`DELETE` for every individual row.'
+
+      def_node_matcher :destroy_all?, <<~PATTERN
+        (send {send ivar lvar const} :destroy_all ...)
+      PATTERN
+
+      def on_send(node)
+        return unless destroy_all?(node)
+
+        add_offense(node, location: :expression)
+      end
+    end
+  end
+end
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index a427208cdab..88c9bbf24f4 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -27,3 +27,4 @@ require_relative 'cop/project_path_helper'
 require_relative 'cop/rspec/env_assignment'
 require_relative 'cop/rspec/factories_in_migration_specs'
 require_relative 'cop/sidekiq_options_queue'
+require_relative 'cop/destroy_all'
diff --git a/spec/rubocop/cop/destroy_all_spec.rb b/spec/rubocop/cop/destroy_all_spec.rb
new file mode 100644
index 00000000000..153a5a863cf
--- /dev/null
+++ b/spec/rubocop/cop/destroy_all_spec.rb
@@ -0,0 +1,43 @@
+require 'spec_helper'
+require 'rubocop'
+require 'rubocop/rspec/support'
+require_relative '../../../rubocop/cop/destroy_all'
+
+describe RuboCop::Cop::DestroyAll do
+  include CopHelper
+
+  subject(:cop) { described_class.new }
+
+  it 'flags the use of destroy_all with a send receiver' do
+    inspect_source('foo.destroy_all')
+
+    expect(cop.offenses.size).to eq(1)
+  end
+
+  it 'flags the use of destroy_all with a constant receiver' do
+    inspect_source('User.destroy_all')
+
+    expect(cop.offenses.size).to eq(1)
+  end
+
+  it 'flags the use of destroy_all when passing arguments' do
+    inspect_source('User.destroy_all([])')
+
+    expect(cop.offenses.size).to eq(1)
+  end
+
+  it 'flags the use of destroy_all with a local variable receiver' do
+    inspect_source(<<~RUBY)
+    users = User.all
+    users.destroy_all
+    RUBY
+
+    expect(cop.offenses.size).to eq(1)
+  end
+
+  it 'does not flag the use of delete_all' do
+    inspect_source('foo.delete_all')
+
+    expect(cop.offenses).to be_empty
+  end
+end