Unlink a project from a fork network when it's source was deleted.

app/models/fork_network.rb

@@ -12,4 +12,8 @@ class ForkNetwork < ActiveRecord::Base
   def find_forks_in(other_projects)
     projects.where(id: other_projects)
   end
+
+  def merge_requests
+    MergeRequest.where(target_project: projects)
+  end
 end

app/services/projects/unlink_fork_service.rb

@@ -3,18 +3,24 @@ module Projects
     def execute
       return unless @project.forked?
 
-      @project.forked_from_project.lfs_objects.find_each do |lfs_object|
-        lfs_object.projects << @project
+      if fork_source = @project.fork_source
+        fork_source.lfs_objects.find_each do |lfs_object|
+          lfs_object.projects << @project
+        end
+
+        refresh_forks_count(fork_source)
       end
 
-      merge_requests = @project.forked_from_project.merge_requests.opened.from_project(@project)
+      merge_requests = @project.fork_network
+                         .merge_requests
+                         .opened
+                         .where.not(target_project: @project)
+                         .from_project(@project)
 
       merge_requests.each do |mr|
         ::MergeRequests::CloseService.new(@project, @current_user).execute(mr)
       end
 
-      refresh_forks_count(@project.forked_from_project)
-
       @project.fork_network_member.destroy
       @project.forked_project_link.destroy
     end

spec/models/fork_network_spec.rb

@@ -24,6 +24,16 @@ describe ForkNetwork do
     end
   end
 
+  describe '#merge_requests' do
+    it 'finds merge requests within the fork network' do
+      project = create(:project)
+      forked_project = fork_project(project)
+      merge_request = create(:merge_request, source_project: forked_project, target_project: project)
+
+      expect(project.fork_network.merge_requests).to include(merge_request)
+    end
+  end
+
   context 'for a deleted project' do
     it 'keeps the fork network' do
       project = create(:project, :public)

spec/services/projects/unlink_fork_service_spec.rb

@@ -12,6 +12,9 @@ describe Projects::UnlinkForkService do
 
   context 'with opened merge request on the source project' do
     let(:merge_request) { create(:merge_request, source_project: forked_project, target_project: fork_link.forked_from_project) }
+    let(:merge_request2) { create(:merge_request, source_project: forked_project, target_project: fork_project(project)) }
+    let(:merge_request_in_fork) { create(:merge_request, source_project: forked_project, target_project: forked_project) }
+
     let(:mr_close_service) { MergeRequests::CloseService.new(forked_project, user) }
 
     before do
@@ -22,9 +25,14 @@ describe Projects::UnlinkForkService do
 
     it 'close all pending merge requests' do
       expect(mr_close_service).to receive(:execute).with(merge_request)
+      expect(mr_close_service).to receive(:execute).with(merge_request2)
 
       subject.execute
     end
+
+    it 'does not close merge requests for the project being unlinked' do
+      expect(mr_close_service).not_to receive(:execute).with(merge_request_in_fork)
+    end
   end
 
   it 'remove fork relation' do
@@ -53,4 +61,14 @@ describe Projects::UnlinkForkService do
 
     expect(source.forks_count).to be_zero
   end
+
+  context 'when the original project was deleted' do
+    it 'does not fail when the original project is deleted' do
+      source = forked_project.forked_from_project
+      source.destroy
+      forked_project.reload
+
+      expect { subject.execute }.not_to raise_error
+    end
+  end
 end