Remove re-use of resolver in mutation

Re-using resolvers anywhere is an anti-pattern (and should be completely
banned with a cop) - they do not compose well at all, and calling them
correctly is practically impossible.

And in any case, mutations do not need their
features (laziness, parallel computation) - instead the re-usable
elements are the same as throughout our application: finders and
services.

This replaces the user of a resolver with a finder, and a plain
find_by_full_path, leaving us with simpler code that is easier to follow
and allocates less garbage.

This work was incidental to
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40088
and has been extracted from there.

app/graphql/mutations/alert_management/base.rb

@@ -4,7 +4,6 @@ module Mutations
   module AlertManagement
     class Base < BaseMutation
       include Gitlab::Utils::UsageData
-      include ResolvesProject
 
       argument :project_path, GraphQL::ID_TYPE,
                required: true,
@@ -33,13 +32,12 @@ module Mutations
 
       private
 
-      def find_object(project_path:, iid:)
-        project = resolve_project(full_path: project_path)
+      def find_object(project_path:, **args)
+        project = Project.find_by_full_path(project_path)
 
         return unless project
 
-        resolver = Resolvers::AlertManagement::AlertResolver.single.new(object: project, context: context, field: nil)
-        resolver.resolve(iid: iid)
+        ::AlertManagement::AlertsFinder.new(current_user, project, args).execute.first
       end
     end
   end

app/graphql/mutations/alert_management/update_alert_status.rb

@@ -9,9 +9,9 @@ module Mutations
                required: true,
                description: 'The status to set the alert'
 
-      def resolve(args)
-        alert = authorized_find!(project_path: args[:project_path], iid: args[:iid])
-        result = update_status(alert, args[:status])
+      def resolve(project_path:, iid:, status:)
+        alert = authorized_find!(project_path: project_path, iid: iid)
+        result = update_status(alert, status)
 
         track_usage_event(:incident_management_alert_status_changed, current_user.id)
 

spec/graphql/mutations/alert_management/update_alert_status_spec.rb

@@ -37,8 +37,8 @@ RSpec.describe Mutations::AlertManagement::UpdateAlertStatus do
       context 'error occurs when updating' do
         it 'returns the alert with errors' do
           # Stub an error on the alert
-          allow_next_instance_of(Resolvers::AlertManagement::AlertResolver) do |resolver|
-            allow(resolver).to receive(:resolve).and_return(alert)
+          allow_next_instance_of(::AlertManagement::AlertsFinder) do |finder|
+            allow(finder).to receive(:execute).and_return([alert])
           end
 
           allow(alert).to receive(:save).and_return(false)