lib: add migration helpers for making a column unique

lib/cops/add_concurrent_index.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+# Copyright (c) 2011-present GitLab B.V.
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+if defined?(RuboCop)
+  module RuboCop
+    module Cop
+      module DS
+        # Cop that checks if `add_concurrent_index` is used with `up`/`down` methods
+        # and not `change`.
+        class AddConcurrentIndex < Cop
+          MSG = '`add_concurrent_index` is not reversible so you must manually define ' \
+            'the `up` and `down` methods in your migration class, using `remove_index` in `down`'
+
+          def on_send(node)
+            dirname = File.dirname(node.location.expression.source_buffer.name)
+            return unless dirname.end_with?('db/migrate')
+
+            name = node.children[1]
+
+            return unless name == :add_concurrent_index
+
+            node.each_ancestor(:def) do |def_node|
+              next unless method_name(def_node) == :change
+
+              add_offense(def_node, location: :name)
+            end
+          end
+
+          def method_name(node)
+            node.children.first
+          end
+        end
+      end
+    end
+  end
+end