Eliminate redundant UnsupportedScopeOrder classes

This change defines UnsupportedScopeOrder class at only one place.

doc/development/database/keyset_pagination.md

@@ -169,7 +169,7 @@ Consider the following scope:
 scope = Issue.where(project_id: 10).order(Gitlab::Database.nulls_last_order('relative_position', 'DESC'))
 # SELECT "issues".* FROM "issues" WHERE "issues"."project_id" = 10 ORDER BY relative_position DESC NULLS LAST
 
-scope.keyset_paginate # raises: Gitlab::Pagination::Keyset::Paginator::UnsupportedScopeOrder: The order on the scope does not support keyset pagination
+scope.keyset_paginate # raises: Gitlab::Pagination::Keyset::UnsupportedScopeOrder: The order on the scope does not support keyset pagination
 ```
 
 The `keyset_paginate` method raises an error because the order value on the query is a custom SQL string and not an [`Arel`](https://www.rubydoc.info/gems/arel) AST node. The keyset library cannot automatically infer configuration values from these kinds of queries.

lib/gitlab/pagination/keyset/in_operator_optimization/query_builder.rb

@@ -6,8 +6,6 @@ module Gitlab
       module InOperatorOptimization
         # rubocop: disable CodeReuse/ActiveRecord
         class QueryBuilder
-          UnsupportedScopeOrder = Class.new(StandardError)
-
           RECURSIVE_CTE_NAME = 'recursive_keyset_cte'
 
           # This class optimizes slow database queries (PostgreSQL specific) where the
@@ -44,14 +42,7 @@ module Gitlab
           def initialize(scope:, array_scope:, array_mapping_scope:, finder_query: nil, values: {})
             @scope, success = Gitlab::Pagination::Keyset::SimpleOrderBuilder.build(scope)
 
-            unless success
-              error_message = <<~MSG
-              The order on the scope does not support keyset pagination. You might need to define a custom Order object.\n
-              See https://docs.gitlab.com/ee/development/database/keyset_pagination.html#complex-order-configuration\n
-              Or the Gitlab::Pagination::Keyset::Order class for examples
-              MSG
-              raise(UnsupportedScopeOrder, error_message)
-            end
+            raise(UnsupportedScopeOrder) unless success
 
             @order = Gitlab::Pagination::Keyset::Order.extract_keyset_order_object(scope)
             @array_scope = array_scope

lib/gitlab/pagination/keyset/iterator.rb

@@ -4,11 +4,9 @@ module Gitlab
   module Pagination
     module Keyset
       class Iterator
-        UnsupportedScopeOrder = Class.new(StandardError)
-
         def initialize(scope:, cursor: {}, use_union_optimization: true, in_operator_optimization_options: nil)
           @scope, success = Gitlab::Pagination::Keyset::SimpleOrderBuilder.build(scope)
-          raise(UnsupportedScopeOrder, 'The order on the scope does not support keyset pagination') unless success
+          raise(UnsupportedScopeOrder) unless success
 
           @cursor = cursor
           @order = Gitlab::Pagination::Keyset::Order.extract_keyset_order_object(scope)

lib/gitlab/pagination/keyset/paginator.rb

@@ -19,8 +19,6 @@ module Gitlab
         FORWARD_DIRECTION = 'n'
         BACKWARD_DIRECTION = 'p'
 
-        UnsupportedScopeOrder = Class.new(StandardError)
-
         # scope                  - ActiveRecord::Relation object with order by clause
         # cursor                 - Encoded cursor attributes as String. Empty value will requests the first page.
         # per_page               - Number of items per page.
@@ -167,7 +165,7 @@ module Gitlab
         def build_scope(scope)
           keyset_aware_scope, success = Gitlab::Pagination::Keyset::SimpleOrderBuilder.build(scope)
 
-          raise(UnsupportedScopeOrder, 'The order on the scope does not support keyset pagination') unless success
+          raise(UnsupportedScopeOrder) unless success
 
           keyset_aware_scope
         end

lib/gitlab/pagination/keyset/unsupported_scope_order.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Pagination
+    module Keyset
+      class UnsupportedScopeOrder < StandardError
+        DEFAULT_ERROR_MESSAGE = <<~MSG
+        The order on the scope does not support keyset pagination. You might need to define a custom Order object.\n
+        See https://docs.gitlab.com/ee/development/database/keyset_pagination.html#complex-order-configuration\n
+        Or the Gitlab::Pagination::Keyset::Order class for examples
+        MSG
+
+        def message
+          DEFAULT_ERROR_MESSAGE
+        end
+      end
+    end
+  end
+end