Create Todos for designs

Allowing Projects::TodosController to create Todos for Designs.

This involved a small change to FinderMethods to refer to an objects
`#to_ability_name` method if defined, as due to its namespacing,
the existing deriving of from `DesignManagement::Design.model_name`
would not work. FinderMethods fallsback to its old deriving method for
when an object does not define `#to_ability_name`.

https://gitlab.com/gitlab-org/gitlab/-/issues/198439

app/controllers/projects/todos_controller.rb

@@ -15,6 +15,9 @@ class Projects::TodosController < Projects::ApplicationController
         IssuesFinder.new(current_user, project_id: @project.id).find(params[:issuable_id])
       when "merge_request"
         MergeRequestsFinder.new(current_user, project_id: @project.id).find(params[:issuable_id])
+      when "design"
+        issue = IssuesFinder.new(current_user, project_id: @project.id).find(params[:issue_id])
+        DesignManagement::DesignsFinder.new(issue, current_user).find(params[:issuable_id])
       end
     end
   end

app/finders/concerns/finder_methods.rb

@@ -30,7 +30,7 @@ module FinderMethods
   def if_authorized(result)
     # Return the result if the finder does not perform authorization checks.
     # this is currently the case in the `MilestoneFinder`
-    return result unless respond_to?(:current_user)
+    return result unless respond_to?(:current_user, true)
 
     if can_read_object?(result)
       result
@@ -44,9 +44,14 @@ module FinderMethods
     # for Todos
     return true unless DeclarativePolicy.has_policy?(object)
 
-    model_name = object&.model_name || model.model_name
+    Ability.allowed?(current_user, :"read_#{to_ability_name(object)}", object)
+  end
+
+  def to_ability_name(object)
+    return object.to_ability_name if object.respond_to?(:to_ability_name)
 
-    Ability.allowed?(current_user, :"read_#{model_name.singular}", object)
+    # Not all objects define `#to_ability_name`, so attempt to derive it:
+    object.model_name.singular
   end
 
   # This fetches the model from the `ActiveRecord::Relation` but does not

app/finders/design_management/designs_finder.rb

@@ -3,6 +3,7 @@
 module DesignManagement
   class DesignsFinder
     include Gitlab::Allowable
+    include FinderMethods
 
     # Params:
     # ids: integer[]

spec/controllers/projects/todos_controller_spec.rb

@@ -3,13 +3,14 @@
 require('spec_helper')
 
 RSpec.describe Projects::TodosController do
-  let(:user)          { create(:user) }
-  let(:project)       { create(:project) }
+  let_it_be(:user)    { create(:user) }
+  let_it_be(:project) { create(:project) }
   let(:issue)         { create(:issue, project: project) }
   let(:merge_request) { create(:merge_request, source_project: project) }
+  let(:design)        { create(:design, project: project, issue: issue) }
   let(:parent)        { project }
 
-  shared_examples 'project todos actions' do
+  shared_examples 'issuable todo actions' do
     it_behaves_like 'todos actions'
 
     context 'when not authorized for resource' do
@@ -40,7 +41,7 @@ RSpec.describe Projects::TodosController do
           format: 'html'
       end
 
-      it_behaves_like 'project todos actions'
+      it_behaves_like 'issuable todo actions'
     end
   end
 
@@ -57,7 +58,31 @@ RSpec.describe Projects::TodosController do
           format: 'html'
       end
 
-      it_behaves_like 'project todos actions'
+      it_behaves_like 'issuable todo actions'
+    end
+  end
+
+  context 'Designs' do
+    include DesignManagementTestHelpers
+
+    before do
+      enable_design_management
+    end
+
+    describe 'POST create' do
+      def post_create
+        post :create,
+          params: {
+            namespace_id: project.namespace,
+            project_id: project,
+            issue_id: issue.id,
+            issuable_id: design.id,
+            issuable_type: 'design'
+          },
+          format: 'html'
+      end
+
+      it_behaves_like 'todos actions'
     end
   end
 end

spec/finders/concerns/finder_methods_spec.rb

@@ -7,8 +7,6 @@ RSpec.describe FinderMethods do
     Class.new do
       include FinderMethods
 
-      attr_reader :current_user
-
       def initialize(user)
         @current_user = user
       end
@@ -16,6 +14,10 @@ RSpec.describe FinderMethods do
       def execute
         Project.all.order(id: :desc)
       end
+
+      private
+
+      attr_reader :current_user
     end
   end