API: Bulk update for issues and merge requests

This MR adds support for bulk update actions for issues and merge
requests. A single API call can be used to update a list of issues
or merge requests

changelogs/unreleased/api-issuable-bulk-update.yml

+---
+title: 'API: Bulk update for issues and MRs'
+merge_request:
+author:
+type: added

lib/api/api.rb

@@ -115,6 +115,7 @@ module API
     mount ::API::GroupVariables
     mount ::API::ImportGithub
     mount ::API::Internal
+    mount ::API::IssuableBulkUpdate
     mount ::API::Issues
     mount ::API::JobArtifacts
     mount ::API::Jobs

lib/api/issuable_bulk_update.rb

+# frozen_string_literal: true
+
+module API
+  class IssuableBulkUpdate < Grape::API
+    params do
+      requires :id, type: String, desc: 'The ID of a project'
+    end
+    resource :projects, requirements: API::NAMESPACE_OR_PROJECT_REQUIREMENTS do
+      %w(issue merge_request).each do |issuable|
+        desc "Updates a list of #{issuable.pluralize}" do
+          detail 'This feature was introduced in 11.9'
+        end
+        params do
+          optional :state_event, type: String, values: %w(reopen close), desc: 'Reopens or closes a resource'
+          optional :milestone_id, type: Integer, desc: 'The milestone ID number'
+          optional :add_label_ids, type: Array[Integer], desc: 'IDs of labels to be added'
+          optional :remove_label_ids, type: Array[Integer], desc: 'IDs of labels to be removed'
+          optional :subscription_event, type: String, values: %w(subscribe unsubscribe),
+                                        desc: 'Subscribes or unsubscribes from a resource'
+
+          if issuable == 'issue'
+            optional :assignee_ids, type: Array[Integer], desc: 'List of assignees IDs'
+            at_least_one_of :state_event, :milestone_id, :add_label_ids, :remove_label_ids,
+                            :subscription_event, :assignee_ids
+          else
+            optional :assignee_id, type: Integer, desc: 'ID of the assignee'
+            at_least_one_of :state_event, :milestone_id, :add_label_ids, :remove_label_ids,
+                            :subscription_event, :assignee_id
+          end
+        end
+        put ":id/#{issuable}/bulk_update" do
+          update_params = declared_params(include_missing: false)
+
+          result = Issuable::BulkUpdateService.new(user_project, current_user, update_params)
+            .execute(issuable)
+          quantity = result[:count]
+
+          if result[:success]
+            status 200
+            { notice: "#{quantity} #{issuable.pluralize(quantity)} updated" }
+          else
+            render_api_error!('Bulk update failed', 400)
+          end
+        end
+      end
+    end
+  end
+end