Enforce use of add_concurrent_foreign_keyconcurrent-foreign-keys

This adds a Rubocop rule to enforce the use of
add_concurrent_foreign_key instead of the regular add_foreign_key
method. This cop has been disabled for existing migrations so we don't
need to change those.

2 files changed, 28 insertions, 0 deletions

diff --git a/rubocop/cop/migration/add_concurrent_foreign_key.rb b/rubocop/cop/migration/add_concurrent_foreign_key.rb
new file mode 100644
index 00000000000..e40a7087a47
--- /dev/null
+++ b/rubocop/cop/migration/add_concurrent_foreign_key.rb
@@ -0,0 +1,27 @@
+require_relative '../../migration_helpers'
+
+module RuboCop
+  module Cop
+    module Migration
+      # Cop that checks if `add_concurrent_foreign_key` is used instead of
+      # `add_foreign_key`.
+      class AddConcurrentForeignKey < RuboCop::Cop::Cop
+        include MigrationHelpers
+
+        MSG = '`add_foreign_key` requires downtime, use `add_concurrent_foreign_key` instead'
+
+        def on_send(node)
+          return unless in_migration?(node)
+
+          name = node.children[1]
+
+          add_offense(node, :selector) if name == :add_foreign_key
+        end
+
+        def method_name(node)
+          node.children.first
+        end
+      end
+    end
+  end
+end
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index aa35fb1701c..d4266d0deae 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -1,4 +1,5 @@
 require_relative 'cop/gem_fetcher'
 require_relative 'cop/migration/add_column'
 require_relative 'cop/migration/add_column_with_default'
+require_relative 'cop/migration/add_concurrent_foreign_key'
 require_relative 'cop/migration/add_index'