Show clusters of ancestors in cluster list page

Show both the cluster(s) of the clusterable, and the cluster(s) of
ancestor groups.

app/controllers/clusters/clusters_controller.rb

@@ -18,8 +18,8 @@ class Clusters::ClustersController < Clusters::BaseController
   STATUS_POLLING_INTERVAL = 10_000
 
   def index
-    clusters = ClustersFinder.new(clusterable, current_user, :all).execute
-    @clusters = clusters.page(params[:page]).per(20)
+    clusters = ClusterAncestorsFinder.new(clusterable.subject, current_user).execute
+    @clusters = Kaminari.paginate_array(clusters).page(params[:page]).per(20)
   end
 
   def new

app/finders/cluster_ancestors_finder.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class ClusterAncestorsFinder
+  def initialize(clusterable, user)
+    @clusterable = clusterable
+    @user = user
+  end
+
+  def execute
+    clusterable.clusters + ancestor_clusters
+  end
+
+  private
+
+  attr_reader :clusterable, :user
+
+  def ancestor_clusters
+    Clusters::Cluster.ancestor_clusters_for_clusterable(clusterable)
+  end
+end

changelogs/unreleased/34758-list-ancestor-clusters.yml

@@ -0,0 +1,5 @@
+---
+title: Show clusters of ancestors in cluster list page
+merge_request: 22996
+author:
+type: changed

spec/finders/cluster_ancestors_finder_spec.rb

@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ClusterAncestorsFinder, '#execute' do
+  let(:group) { create(:group) }
+  let(:project) { create(:project, group: group) }
+  let(:user) { create(:user) }
+
+  let!(:project_cluster) do
+    create(:cluster, :provided_by_user, cluster_type: :project_type, projects: [project])
+  end
+
+  let!(:group_cluster) do
+    create(:cluster, :provided_by_user, cluster_type: :group_type, groups: [group])
+  end
+
+  subject { described_class.new(clusterable, user).execute }
+
+  context 'for a project' do
+    let(:clusterable) { project }
+
+    it 'returns the project clusters followed by group clusters' do
+      is_expected.to eq([project_cluster, group_cluster])
+    end
+
+    context 'nested groups', :nested_groups do
+      let(:group) { create(:group, parent: parent_group) }
+      let(:parent_group) { create(:group) }
+
+      let!(:parent_group_cluster) do
+        create(:cluster, :provided_by_user, cluster_type: :group_type, groups: [parent_group])
+      end
+
+      it 'returns the project clusters followed by group clusters ordered ascending the hierarchy' do
+        is_expected.to eq([project_cluster, group_cluster, parent_group_cluster])
+      end
+    end
+  end
+
+  context 'for a group' do
+    let(:clusterable) { group }
+
+    it 'returns the list of group clusters' do
+      is_expected.to eq([group_cluster])
+    end
+
+    context 'nested groups', :nested_groups do
+      let(:group) { create(:group, parent: parent_group) }
+      let(:parent_group) { create(:group) }
+
+      let!(:parent_group_cluster) do
+        create(:cluster, :provided_by_user, cluster_type: :group_type, groups: [parent_group])
+      end
+
+      it 'returns the list of group clusters ordered ascending the hierarchy' do
+        is_expected.to eq([group_cluster, parent_group_cluster])
+      end
+    end
+  end
+end