Refactor: model errors for multi cluster validation

The current approach requires catching exceptions to handle these errors
and callers are already handling model validations so it seems more
appropriate.  Also it seemed to convoluted to add this logic directly to
the model since the model needs to check too many possible associations
to determine whether or not there are more than one cluster since the
model doesn't know what it's being created on. Additionally we only
wanted to validate during create to avoid the risk of existing models
becoming invalid by many different edge cases.

6 files changed, 23 insertions, 42 deletions

diff --git a/app/policies/clusters/instance_policy.rb b/app/policies/clusters/instance_policy.rb
index f72096e8fc6..bd7ff413afe 100644
--- a/app/policies/clusters/instance_policy.rb
+++ b/app/policies/clusters/instance_policy.rb
@@ -2,11 +2,6 @@
 
 module Clusters
   class InstancePolicy < BasePolicy
-    include ClusterableActions
-
-    condition(:has_clusters, scope: :subject) { clusterable_has_clusters? }
-    condition(:can_have_multiple_clusters) { multiple_clusters_available? }
-
     rule { admin }.policy do
       enable :read_cluster
       enable :add_cluster
@@ -14,7 +9,5 @@ module Clusters
       enable :update_cluster
       enable :admin_cluster
     end
-
-    rule { ~can_have_multiple_clusters & has_clusters }.prevent :add_cluster
   end
 end
diff --git a/app/policies/concerns/clusterable_actions.rb b/app/policies/concerns/clusterable_actions.rb
deleted file mode 100644
index 08ddd742ea9..00000000000
--- a/app/policies/concerns/clusterable_actions.rb
+++ /dev/null
@@ -1,14 +0,0 @@
-# frozen_string_literal: true
-
-module ClusterableActions
-  private
-
-  # Overridden on EE module
-  def multiple_clusters_available?
-    false
-  end
-
-  def clusterable_has_clusters?
-    !subject.clusters.empty?
-  end
-end
diff --git a/app/policies/group_policy.rb b/app/policies/group_policy.rb
index ea86858181d..9219283992f 100644
--- a/app/policies/group_policy.rb
+++ b/app/policies/group_policy.rb
@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 
 class GroupPolicy < BasePolicy
-  include ClusterableActions
-
   desc "Group is public"
   with_options scope: :subject, score: 0
   condition(:public_group) { @subject.public? }
@@ -29,9 +27,6 @@ class GroupPolicy < BasePolicy
     GroupProjectsFinder.new(group: @subject, current_user: @user, options: { include_subgroups: true, only_owned: true }).execute.any?
   end
 
-  condition(:has_clusters, scope: :subject) { clusterable_has_clusters? }
-  condition(:can_have_multiple_clusters) { multiple_clusters_available? }
-
   with_options scope: :subject, score: 0
   condition(:request_access_enabled) { @subject.request_access_enabled }
 
@@ -121,8 +116,6 @@ class GroupPolicy < BasePolicy
 
   rule { owner & (~share_with_group_locked | ~has_parent | ~parent_share_with_group_locked | can_change_parent_share_with_group_lock) }.enable :change_share_with_group_lock
 
-  rule { ~can_have_multiple_clusters & has_clusters }.prevent :add_cluster
-
   rule { developer & developer_maintainer_access }.enable :create_projects
   rule { create_projects_disabled }.prevent :create_projects
 
diff --git a/app/policies/project_policy.rb b/app/policies/project_policy.rb
index 3c9ffbb2065..e79bac6bee3 100644
--- a/app/policies/project_policy.rb
+++ b/app/policies/project_policy.rb
@@ -2,7 +2,6 @@
 
 class ProjectPolicy < BasePolicy
   extend ClassMethods
-  include ClusterableActions
 
   READONLY_FEATURES_WHEN_ARCHIVED = %i[
     issue
@@ -114,9 +113,6 @@ class ProjectPolicy < BasePolicy
     @subject.feature_available?(:merge_requests, @user)
   end
 
-  condition(:has_clusters, scope: :subject) { clusterable_has_clusters? }
-  condition(:can_have_multiple_clusters) { multiple_clusters_available? }
-
   condition(:internal_builds_disabled) do
     !@subject.builds_enabled?
   end
@@ -430,8 +426,6 @@ class ProjectPolicy < BasePolicy
     (~guest & can?(:read_project_for_iids) & merge_requests_visible_to_user) | can?(:read_merge_request)
   end.enable :read_merge_request_iid
 
-  rule { ~can_have_multiple_clusters & has_clusters }.prevent :add_cluster
-
   rule { ~can?(:read_cross_project) & ~classification_label_authorized }.policy do
     # Preventing access here still allows the projects to be listed. Listing
     # projects doesn't check the `:read_project` ability. But instead counts
diff --git a/app/presenters/clusterable_presenter.rb b/app/presenters/clusterable_presenter.rb
index 34bdf156623..fff6d23efdf 100644
--- a/app/presenters/clusterable_presenter.rb
+++ b/app/presenters/clusterable_presenter.rb
@@ -13,7 +13,8 @@ class ClusterablePresenter < Gitlab::View::Presenter::Delegated
   end
 
   def can_add_cluster?
-    can?(current_user, :add_cluster, clusterable)
+    can?(current_user, :add_cluster, clusterable) &&
+      (has_no_clusters? || multiple_clusters_available?)
   end
 
   def can_create_cluster?
@@ -63,4 +64,15 @@ class ClusterablePresenter < Gitlab::View::Presenter::Delegated
   def learn_more_link
     raise NotImplementedError
   end
+
+  private
+
+  # Overridden on EE module
+  def multiple_clusters_available?
+    false
+  end
+
+  def has_no_clusters?
+    clusterable.clusters.empty?
+  end
 end
diff --git a/app/services/clusters/create_service.rb b/app/services/clusters/create_service.rb
index 886e484caaf..5fb5e15c32d 100644
--- a/app/services/clusters/create_service.rb
+++ b/app/services/clusters/create_service.rb
@@ -10,24 +10,27 @@ module Clusters
 
     def execute(access_token: nil)
       raise ArgumentError, 'Unknown clusterable provided' unless clusterable
-      raise ArgumentError, _('Instance does not support multiple Kubernetes clusters') unless can_create_cluster?
 
       cluster_params = params.merge(user: current_user).merge(clusterable_params)
       cluster_params[:provider_gcp_attributes].try do |provider|
         provider[:access_token] = access_token
       end
 
-      create_cluster(cluster_params).tap do |cluster|
-        ClusterProvisionWorker.perform_async(cluster.id) if cluster.persisted?
+      cluster = Clusters::Cluster.new(cluster_params)
+
+      unless can_create_cluster?
+        cluster.errors.add(:base, _('Instance does not support multiple Kubernetes clusters'))
       end
-    end
 
-    private
+      return cluster if cluster.errors.present?
 
-    def create_cluster(cluster_params)
-      Clusters::Cluster.create(cluster_params)
+      cluster.tap do |cluster|
+        cluster.save && ClusterProvisionWorker.perform_async(cluster.id)
+      end
     end
 
+    private
+
     def clusterable
       @clusterable ||= params.delete(:clusterable)
     end