BulkImports: avoid infinity recursion on group migration

The current subgroup migration strategy works iteratively, which means
that each level of a group tree is imported before moving to the next
level.

This becomes a problem when the target group is within the source group,
which creates a _infinity_ loop of import.

>> Example:

Given a group tree like:

- Group A
  - Group B
  - Group C
    - Group X
    - Group Y

If one decide to import the Group A into Group B, a recursion will
happen, making the import stop only when the depth limit is achieved or
some other database constraint, like the size of a group path.

- Group A
  - Group B
    - Group A
      - Group B
        - Group A
          - Group B
            - Group A
              - Group B
                - ...
              - Group C
                - Group X
                - Group Y
          - Group C
            - Group X
            - Group Y
      - Group C
        - Group X
        - Group Y
  - Group C
    - Group X
    - Group Y

To fix that, destination namespaces cannot be a descendant of the source
group.

Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/300445

app/models/bulk_imports/entity.rb

@@ -43,6 +43,8 @@ class BulkImports::Entity < ApplicationRecord
   validate :validate_parent_is_a_group, if: :parent
   validate :validate_imported_entity_type
 
+  validate :validate_destination_namespace_ascendency, if: :group_entity?
+
   enum source_type: { group_entity: 0, project_entity: 1 }
 
   state_machine :status, initial: :created do
@@ -107,4 +109,17 @@ class BulkImports::Entity < ApplicationRecord
       )
     end
   end
+
+  def validate_destination_namespace_ascendency
+    source = Group.find_by_full_path(source_full_path)
+
+    return unless source
+
+    if source.self_and_descendants.any? { |namespace| namespace.full_path == destination_namespace }
+      errors.add(
+        :destination_namespace,
+        s_('BulkImport|destination group cannot be part of the source group tree')
+      )
+    end
+  end
 end

changelogs/unreleased/kassio-bulkimports-avoid-recursive-group-migration.yml

+---
+title: 'BulkImports: avoid infinity recursion on group migration'
+merge_request: 52931
+author:
+type: fixed

locale/gitlab.pot

@@ -4926,6 +4926,9 @@ msgstr ""
 msgid "BulkImport|Update of import statuses with realtime changes failed"
 msgstr ""
 
+msgid "BulkImport|destination group cannot be part of the source group tree"
+msgstr ""
+
 msgid "BulkImport|expected an associated Group but has an associated Project"
 msgstr ""
 

spec/models/bulk_imports/entity_spec.rb

@@ -81,6 +81,37 @@ RSpec.describe BulkImports::Entity, type: :model do
         expect(entity.errors).to include(:parent)
       end
     end
+
+    context 'validate destination namespace of a group_entity' do
+      it 'is invalid if destination namespace is the source namespace' do
+        group_a = create(:group, path: 'group_a')
+
+        entity = build(
+          :bulk_import_entity,
+          :group_entity,
+          source_full_path: group_a.full_path,
+          destination_namespace: group_a.full_path
+        )
+
+        expect(entity).not_to be_valid
+        expect(entity.errors).to include(:destination_namespace)
+      end
+
+      it 'is invalid if destination namespace is a descendant of the source' do
+        group_a = create(:group, path: 'group_a')
+        group_b = create(:group, parent: group_a, path: 'group_b')
+
+        entity = build(
+          :bulk_import_entity,
+          :group_entity,
+          source_full_path: group_a.full_path,
+          destination_namespace: group_b.full_path
+        )
+
+        expect(entity).not_to be_valid
+        expect(entity.errors).to include(:destination_namespace)
+      end
+    end
   end
 
   describe "#update_tracker_for" do