From 1ab33b15d1f1cc6ce69514e545da1348fd750771 Mon Sep 17 00:00:00 2001
From: Sean McGivern <sean@gitlab.com>
Date: Mon, 11 Dec 2017 16:34:51 +0000
Subject: Add cop for use of remove_column

remove_column should only be used in the up (or change) step of a migration if
it's a post-deployment migration. Otherwise there will be downtime due to the
ActiveRecord column cache, which we can avoid by using the IgnorableColumn
concern in combination with a post-deployment migration.
---
 rubocop/cop/migration/remove_column.rb | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 rubocop/cop/migration/remove_column.rb

(limited to 'rubocop/cop/migration')

diff --git a/rubocop/cop/migration/remove_column.rb b/rubocop/cop/migration/remove_column.rb
new file mode 100644
index 00000000000..e53eb2e07b2
--- /dev/null
+++ b/rubocop/cop/migration/remove_column.rb
@@ -0,0 +1,30 @@
+require_relative '../../migration_helpers'
+
+module RuboCop
+  module Cop
+    module Migration
+      # Cop that checks if remove_column is used in a regular (not
+      # post-deployment) migration.
+      class RemoveColumn < RuboCop::Cop::Cop
+        include MigrationHelpers
+
+        MSG = '`remove_column` must only be used in post-deployment migrations'.freeze
+
+        def on_def(node)
+          def_method = node.children[0]
+
+          return unless in_migration?(node) && !in_post_deployment_migration?(node)
+          return unless def_method == :change || def_method == :up
+
+          node.each_descendant(:send) do |send_node|
+            send_method = send_node.children[1]
+
+            if send_method == :remove_column
+              add_offense(send_node, :selector)
+            end
+          end
+        end
+      end
+    end
+  end
+end
-- 
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