Add IgnorableColumns concern

This is basically only documenting when column-ignores can be removed
again

Relates to https://gitlab.com/gitlab-org/gitlab/issues/33127

app/models/ci/build.rb

@@ -13,17 +13,11 @@ module Ci
     include Importable
     include Gitlab::Utils::StrongMemoize
     include HasRef
+    include IgnorableColumns
 
     BuildArchivedError = Class.new(StandardError)
 
-    self.ignored_columns += %i[
-      artifacts_file
-      artifacts_file_store
-      artifacts_metadata
-      artifacts_metadata_store
-      artifacts_size
-      commands
-    ]
+    ignore_columns :artifacts_file, :artifacts_file_store, :artifacts_metadata, :artifacts_metadata_store, :artifacts_size, :commands, remove_after: '2019-12-15', remove_with: '12.7'
 
     belongs_to :project, inverse_of: :builds
     belongs_to :runner

app/models/ci/runner.rb

@@ -8,6 +8,7 @@ module Ci
     include ChronicDurationAttribute
     include FromUnion
     include TokenAuthenticatable
+    include IgnorableColumns
 
     add_authentication_token_field :token, encrypted: -> { Feature.enabled?(:ci_runners_tokens_optional_encryption, default_enabled: true) ? :optional : :required }
 
@@ -35,7 +36,7 @@ module Ci
 
     FORM_EDITABLE = %i[description tag_list active run_untagged locked access_level maximum_timeout_human_readable].freeze
 
-    self.ignored_columns += %i[is_shared]
+    ignore_columns :is_shared, remove_after: '2019-12-15', remove_with: '12.6'
 
     has_many :builds
     has_many :runner_projects, inverse_of: :runner, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent

app/models/concerns/ignorable_columns.rb

+# frozen_string_literal: true
+
+module IgnorableColumns
+  extend ActiveSupport::Concern
+
+  class_methods do
+    # Ignore database columns in a model
+    #
+    # Indicate the earliest date and release we can stop ignoring the column with +remove_after+ (a date string) and +remove_with+ (a release)
+    def ignore_columns(*columns, remove_after:, remove_with:)
+      raise 'Please indicate when we can stop ignoring columns with remove_after, example: ignore_columns(:name, remove_after: \'2019-12-01\', remove_with: \'12.6\')' unless remove_after && remove_with
+
+      self.ignored_columns += columns
+    end
+  end
+end

app/models/deploy_key.rb

@@ -2,6 +2,7 @@
 
 class DeployKey < Key
   include FromUnion
+  include IgnorableColumns
 
   has_many :deploy_keys_projects, inverse_of: :deploy_key, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
   has_many :projects, through: :deploy_keys_projects
@@ -10,7 +11,7 @@ class DeployKey < Key
   scope :are_public,  -> { where(public: true) }
   scope :with_projects, -> { includes(deploy_keys_projects: { project: [:route, :namespace] }) }
 
-  self.ignored_columns += %i[can_push]
+  ignore_columns :can_push, remove_after: '2019-12-15', remove_with: '12.6'
 
   accepts_nested_attributes_for :deploy_keys_projects
 

app/models/project.rb

@@ -31,6 +31,7 @@ class Project < ApplicationRecord
   include FeatureGate
   include OptionallySearch
   include FromUnion
+  include IgnorableColumns
   extend Gitlab::Cache::RequestCache
 
   extend Gitlab::ConfigHelper
@@ -64,7 +65,7 @@ class Project < ApplicationRecord
 
   # TODO: remove once GitLab 12.5 is released
   # https://gitlab.com/gitlab-org/gitlab/issues/34638
-  self.ignored_columns += %i[merge_requests_require_code_owner_approval]
+  ignore_columns :merge_requests_require_code_owner_approval, remove_after: '2019-12-01', remove_with: '12.6'
 
   default_value_for :archived, false
   default_value_for :resolve_outdated_diff_discussions, false

ee/app/models/ee/project.rb

@@ -11,6 +11,7 @@ module EE
     extend ::Gitlab::Cache::RequestCache
     include ::Gitlab::Utils::StrongMemoize
     include ::EE::GitlabRoutingHelper # rubocop: disable Cop/InjectEnterpriseEditionModule
+    include IgnorableColumns
 
     GIT_LFS_DOWNLOAD_OPERATION = 'download'.freeze
 
@@ -23,10 +24,7 @@ module EE
       include DeprecatedApprovalsBeforeMerge
       include UsageStatistics
 
-      self.ignored_columns += %i[
-        mirror_last_update_at
-        mirror_last_successful_update_at
-      ]
+      ignore_columns :mirror_last_update_at, :mirror_last_successful_update_at, remove_after: '2019-12-15', remove_with: '12.6'
 
       before_save :set_override_pull_mirror_available, unless: -> { ::Gitlab::CurrentSettings.mirror_available }
       before_save :set_next_execution_timestamp_to_now, if: ->(project) { project.mirror? && project.mirror_changed? && project.import_state }

ee/app/models/operations/feature_flags_client.rb

@@ -3,9 +3,10 @@
 module Operations
   class FeatureFlagsClient < ApplicationRecord
     include TokenAuthenticatable
+    include IgnorableColumns
 
     self.table_name = 'operations_feature_flags_clients'
-    self.ignored_columns += %i[token]
+    ignore_columns :token, remove_after: '2019-12-15', remove_with: '12.6'
 
     belongs_to :project
 

spec/models/concerns/ignorable_columns_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe IgnorableColumns do
+  class User < ApplicationRecord
+    include IgnorableColumns
+  end
+
+  it 'adds columns to ignored_columns' do
+    expect do
+      User.ignore_columns(:name, :created_at, remove_after: '2019-12-01', remove_with: '12.6')
+    end.to change { User.ignored_columns }.from([]).to(%w(name created_at))
+  end
+
+  it 'requires remove_after attribute to be set' do
+    expect { User.ignore_columns(:name, remove_after: nil, remove_with: 12.6) }.to raise_error
+  end
+
+  it 'requires remove_with attribute to be set' do
+    expect { User.ignore_columns(:name, remove_after: '2019-12-01', remove_with: nil) }.to raise_error
+  end
+
+end
\ No newline at end of file