Don't try to create fork network memberships for forks of forksbvl-fork-network-memberships-for-deleted-source

In case the root project of a Fork-of-fork is deleted, the ForkNetwork
and the membership for that fork network is never created. In this
case we shouldn't try to create the membership, since the parent
membership will never be created.

This means that these fork networks will be lost.

3 files changed, 24 insertions, 2 deletions

diff --git a/changelogs/unreleased/bvl-fork-network-memberships-for-deleted-source.yml b/changelogs/unreleased/bvl-fork-network-memberships-for-deleted-source.yml
new file mode 100644
index 00000000000..ae1eb3aedd5
--- /dev/null
+++ b/changelogs/unreleased/bvl-fork-network-memberships-for-deleted-source.yml
@@ -0,0 +1,5 @@
+---
+title: Don't try to create fork network memberships for forks with a missing source
+merge_request: 15366
+author:
+type: fixed
diff --git a/lib/gitlab/background_migration/create_fork_network_memberships_range.rb b/lib/gitlab/background_migration/create_fork_network_memberships_range.rb
index c88eb9783ed..67a39d28944 100644
--- a/lib/gitlab/background_migration/create_fork_network_memberships_range.rb
+++ b/lib/gitlab/background_migration/create_fork_network_memberships_range.rb
@@ -51,10 +51,20 @@ module Gitlab
             FROM projects
             WHERE forked_project_links.forked_from_project_id = projects.id
           )
+          AND NOT EXISTS (
+            SELECT true
+            FROM forked_project_links AS parent_links
+            WHERE parent_links.forked_to_project_id = forked_project_links.forked_from_project_id
+            AND NOT EXISTS (
+              SELECT true
+              FROM projects
+              WHERE parent_links.forked_from_project_id = projects.id
+            )
+          )
           AND forked_project_links.id BETWEEN #{start_id} AND #{end_id}
         MISSING_MEMBERS
 
-        ForkNetworkMember.count_by_sql(count_sql) > 0
+        ForkedProjectLink.count_by_sql(count_sql) > 0
       end
 
       def log(message)
diff --git a/spec/lib/gitlab/background_migration/create_fork_network_memberships_range_spec.rb b/spec/lib/gitlab/background_migration/create_fork_network_memberships_range_spec.rb
index 1a4ea2bac48..79d2c071446 100644
--- a/spec/lib/gitlab/background_migration/create_fork_network_memberships_range_spec.rb
+++ b/spec/lib/gitlab/background_migration/create_fork_network_memberships_range_spec.rb
@@ -93,7 +93,14 @@ describe Gitlab::BackgroundMigration::CreateForkNetworkMembershipsRange, :migrat
   end
 
   it 'knows it is finished for this range' do
-    expect(migration.missing_members?(1, 7)).to be_falsy
+    expect(migration.missing_members?(1, 8)).to be_falsy
+  end
+
+  it 'does not miss members for forks of forks for which the root was deleted' do
+    forked_project_links.create(id: 9, forked_from_project_id: base1_fork1.id, forked_to_project_id: create(:project).id)
+    base1.destroy
+
+    expect(migration.missing_members?(7, 10)).to be_falsy
   end
 
   context 'with more forks' do