Preserve custom .gitlab-ci.yml config path when forking

Fixes: #22875, #30242

app/services/projects/fork_service.rb

@@ -43,6 +43,7 @@ module Projects
         shared_runners_enabled:    @project.shared_runners_enabled,
         namespace_id:              target_namespace.id,
         fork_network:              fork_network,
+        ci_config_path:            @project.ci_config_path,
         # We need to set ci_default_git_depth to 0 for the forked project when
         # @project.ci_default_git_depth is nil in order to keep the same behaviour
         # and not get ProjectCiCdSetting::DEFAULT_GIT_DEPTH set on create

changelogs/unreleased/fork_gitlab_ci.yml

+---
+title: Preserve custom .gitlab-ci.yml config path when forking.
+merge_request: 17817
+author: Mathieu Parent
+type: added

spec/services/projects/fork_service_spec.rb

@@ -50,6 +50,7 @@ describe Projects::ForkService do
           it { expect(to_project.star_count).to be_zero }
           it { expect(to_project.description).to eq(@from_project.description) }
           it { expect(to_project.avatar.file).to be_exists }
+          it { expect(to_project.ci_config_path).to eq(@from_project.ci_config_path) }
 
           # This test is here because we had a bug where the from-project lost its
           # avatar after being forked.
@@ -215,7 +216,8 @@ describe Projects::ForkService do
         @project     = create(:project, :repository,
                               creator_id: @group_owner.id,
                               star_count: 777,
-                              description: 'Wow, such a cool project!')
+                              description: 'Wow, such a cool project!',
+                              ci_config_path: 'debian/salsa-ci.yml')
         @group = create(:group)
         @group.add_user(@group_owner, GroupMember::OWNER)
         @group.add_user(@developer,   GroupMember::DEVELOPER)
@@ -228,14 +230,15 @@ describe Projects::ForkService do
         it 'group owner successfully forks project into the group' do
           to_project = fork_project(@project, @group_owner, @opts)
 
-          expect(to_project).to             be_persisted
-          expect(to_project.errors).to      be_empty
-          expect(to_project.owner).to       eq(@group)
-          expect(to_project.namespace).to   eq(@group)
-          expect(to_project.name).to        eq(@project.name)
-          expect(to_project.path).to        eq(@project.path)
-          expect(to_project.description).to eq(@project.description)
-          expect(to_project.star_count).to  be_zero
+          expect(to_project).to                be_persisted
+          expect(to_project.errors).to         be_empty
+          expect(to_project.owner).to          eq(@group)
+          expect(to_project.namespace).to      eq(@group)
+          expect(to_project.name).to           eq(@project.name)
+          expect(to_project.path).to           eq(@project.path)
+          expect(to_project.description).to    eq(@project.description)
+          expect(to_project.ci_config_path).to eq(@project.ci_config_path)
+          expect(to_project.star_count).to     be_zero
         end
       end