Use a query builder rather than a PORO to create FDW queries

We were using the PORO to group a bunch of static methods,
and we never instantiate it, so a query builder makes much
more sense in this context.

ee/app/finders/geo/project_registry_pending_verification_finder.rb

@@ -21,9 +21,10 @@ module Geo
     def execute
       return Geo::ProjectRegistry.none unless valid_shard?
 
-      current_node.project_registries
-        .merge(Geo::Fdw::ProjectRegistry.registries_pending_verification)
-        .merge(Geo::Fdw::ProjectRegistry.within_shards(shard_name))
+      Gitlab::Geo::Fdw::ProjectRegistryQueryBuilder
+        .new(current_node.project_registries)
+        .registries_pending_verification
+        .within_shards(shard_name)
         .limit(batch_size)
     end
     # rubocop:enable CodeReuse/ActiveRecord

ee/app/models/geo/fdw/geo_node.rb

@@ -29,7 +29,7 @@ module Geo
       private
 
       def registries_for_selected_namespaces
-        Geo::Fdw::ProjectRegistry
+        Gitlab::Geo::Fdw::ProjectRegistryQueryBuilder.new
           .within_namespaces(selected_namespaces_and_descendants.select(:id))
       end
 
@@ -57,7 +57,8 @@ module Geo
       end
 
       def registries_for_selected_shards
-        Geo::Fdw::ProjectRegistry.within_shards(selective_sync_shards)
+        Gitlab::Geo::Fdw::ProjectRegistryQueryBuilder.new
+          .within_shards(selective_sync_shards)
       end
 
       def fdw_namespaces_table

ee/app/models/geo/fdw/project.rb

@@ -17,6 +17,14 @@ module Geo
         def search(query)
           fuzzy_search(query, [:path, :name, :description])
         end
+
+        def within_namespaces(namespace_ids)
+          where(arel_table.name => { namespace_id: namespace_ids })
+        end
+
+        def within_shards(shard_names)
+          where(repository_storage: Array(shard_names))
+        end
       end
     end
   end

ee/app/models/geo/fdw/project_registry.rb → ee/lib/gitlab/geo/fdw/project_registry_query_builder.rb

 # frozen_string_literal: true
 
-module Geo
-  module Fdw
-    class ProjectRegistry
-      class << self
+# Builder class to create composable queries using FDW to
+# retrieve project registries.
+#
+# Basic usage:
+#
+#     Gitlab::Geo::Fdw::ProjectRegistryQueryBuilder
+#       .new(Geo::ProjectRegistry.all)
+#       .registries_pending_verification
+#       .within_shards(selective_sync_shards)
+#
+module Gitlab
+  module Geo
+    class Fdw
+      class ProjectRegistryQueryBuilder < SimpleDelegator
+        attr_reader :query
+
+        def initialize(query = nil)
+          @query = query || base_query
+          super(query)
+        end
+
+        # rubocop:disable CodeReuse/ActiveRecord
         def registries_pending_verification
-          Geo::ProjectRegistry
+          reflect(
+            query
               .joins(fdw_inner_join_projects)
               .joins(fdw_inner_join_repository_state)
               .where(repositories_pending_verification.or(wikis_pending_verification))
+          )
         end
+        # rubocop:enable CodeReuse/ActiveRecord
 
+        # rubocop:disable CodeReuse/ActiveRecord
         def within_namespaces(namespace_ids)
-          Geo::ProjectRegistry
+          reflect(
+            query
               .joins(fdw_inner_join_projects)
-            .where(fdw_projects_table.name => { namespace_id: namespace_ids })
+              .merge(projects_within_namespaces(namespace_ids))
+          )
         end
+        # rubocop:enable CodeReuse/ActiveRecord
 
+        # rubocop:disable CodeReuse/ActiveRecord
         def within_shards(shard_names)
-          Geo::ProjectRegistry
+          reflect(
+            query
               .joins(fdw_inner_join_projects)
-            .where(fdw_projects_table.name => { repository_storage: Array(shard_names) })
+              .merge(projects_within_shards(shard_names))
+          )
         end
+        # rubocop:enable CodeReuse/ActiveRecord
 
         private
 
+        def base_query
+          ::Geo::ProjectRegistry.select(project_registries_table[Arel.star])
+        end
+
+        def reflect(query)
+          self.class.new(query)
+        end
+
         def project_registries_table
-          Geo::ProjectRegistry.arel_table
+          ::Geo::ProjectRegistry.arel_table
         end
 
         def fdw_projects_table
-          Geo::Fdw::Project.arel_table
+          ::Geo::Fdw::Project.arel_table
         end
 
         def fdw_repository_state_table
-          Geo::Fdw::ProjectRepositoryState.arel_table
+          ::Geo::Fdw::ProjectRepositoryState.arel_table
         end
 
         def fdw_inner_join_projects
@@ -51,13 +88,23 @@ module Geo
             .join_sources
         end
 
+        def projects_within_namespaces(namespace_ids)
+          ::Geo::Fdw::Project.within_namespaces(namespace_ids)
+        end
+
+        def projects_within_shards(shard_names)
+          ::Geo::Fdw::Project.within_shards(shard_names)
+        end
+
         def repositories_pending_verification
-          Geo::ProjectRegistry.repositories_pending_verification
+          ::Geo::ProjectRegistry
+            .repositories_pending_verification
             .and(fdw_repository_state_table[:repository_verification_checksum].not_eq(nil))
         end
 
         def wikis_pending_verification
-          Geo::ProjectRegistry.wikis_pending_verification
+          ::Geo::ProjectRegistry
+            .wikis_pending_verification
             .and(fdw_repository_state_table[:wiki_verification_checksum].not_eq(nil))
         end
       end