Validate unique environment scope for instance clusters

https://gitlab.com/gitlab-org/gitlab/merge_requests/20886

app/models/clusters/cluster.rb

@@ -271,6 +271,21 @@ module Clusters
       kubernetes_namespaces.delete_all(:delete_all)
     end
 
+    def clusterable
+      return unless cluster_type
+
+      case cluster_type
+      when 'project_type'
+        project
+      when 'group_type'
+        group
+      when 'instance_type'
+        instance
+      else
+        raise NotImplementedError
+      end
+    end
+
     private
 
     def unique_management_project_environment_scope

changelogs/unreleased/37480-validate-instance-level-cluster-environment-scope.yml

+---
+title: Validate unique environment scope for instance clusters
+merge_request: 20886
+author:
+type: fixed

ee/app/models/ee/clusters/cluster.rb

@@ -12,22 +12,16 @@ module EE
         validate :unique_environment_scope
       end
 
-      def unique_environment_scope
-        if project && project.clusters.where(environment_scope: environment_scope).where.not(id: id).exists?
-          errors.add(:environment_scope, "cannot add duplicated environment scope")
-          return false
-        end
+      def prometheus_adapter
+        application_prometheus
+      end
+
+      private
 
-        if group && group.clusters.where(environment_scope: environment_scope).where.not(id: id).exists?
+      def unique_environment_scope
+        if clusterable.present? && clusterable.clusters.where(environment_scope: environment_scope).where.not(id: id).exists?
           errors.add(:environment_scope, 'cannot add duplicated environment scope')
-          return false
         end
-
-        true
-      end
-
-      def prometheus_adapter
-        application_prometheus
       end
     end
   end

ee/spec/models/ee/clusters/cluster_spec.rb

@@ -61,6 +61,24 @@ describe Clusters::Cluster do
           it { is_expected.to be_truthy }
         end
       end
+
+      context 'for an instance cluster' do
+        before do
+          create(:cluster, :instance, environment_scope: 'product/*')
+        end
+
+        context 'identical environment scope exists' do
+          let(:cluster) { build(:cluster, :instance, environment_scope: 'product/*') }
+
+          it { is_expected.to be_falsey }
+        end
+
+        context 'identical environment scope does not exist' do
+          let(:cluster) { build(:cluster, :instance, environment_scope: '*') }
+
+          it { is_expected.to be_truthy }
+        end
+      end
     end
   end
 end

spec/models/clusters/cluster_spec.rb

@@ -976,4 +976,38 @@ describe Clusters::Cluster, :use_clean_rails_memory_store_caching do
       expect(cluster.kubernetes_namespaces).to be_empty
     end
   end
+
+  describe '#clusterable' do
+    subject { cluster.clusterable }
+
+    context 'project type' do
+      let(:cluster) { create(:cluster, :project) }
+
+      it { is_expected.to eq(cluster.project) }
+    end
+
+    context 'group type' do
+      let(:cluster) { create(:cluster, :group) }
+
+      it { is_expected.to eq(cluster.group) }
+    end
+
+    context 'instance type' do
+      let(:cluster) { create(:cluster, :instance) }
+
+      it { is_expected.to be_a(Clusters::Instance) }
+    end
+
+    context 'unknown type' do
+      let(:cluster) { create(:cluster, :project) }
+
+      before do
+        allow(cluster).to receive(:cluster_type).and_return('unknown_type')
+      end
+
+      it 'raises NotImplementedError' do
+        expect { subject }.to raise_error(NotImplementedError)
+      end
+    end
+  end
 end