Use consistent execution time. Un-null a field

doc/api/graphql/reference/index.md

@@ -10161,7 +10161,7 @@ Describes an incident management on-call schedule.
 | <a id="incidentmanagementoncallscheduledescription"></a>`description` | [`String`](#string) | Description of the on-call schedule. |
 | <a id="incidentmanagementoncallscheduleiid"></a>`iid` | [`ID!`](#id) | Internal ID of the on-call schedule. |
 | <a id="incidentmanagementoncallschedulename"></a>`name` | [`String!`](#string) | Name of the on-call schedule. |
-| <a id="incidentmanagementoncallscheduleoncallusers"></a>`oncallUsers` | [`[UserCore!]!`](#usercore) |  |
+| <a id="incidentmanagementoncallscheduleoncallusers"></a>`oncallUsers` | [`[UserCore!]`](#usercore) |  |
 | <a id="incidentmanagementoncallschedulerotations"></a>`rotations` | [`IncidentManagementOncallRotationConnection!`](#incidentmanagementoncallrotationconnection) | On-call rotations for the on-call schedule. (see [Connections](#connections)) |
 | <a id="incidentmanagementoncallscheduletimezone"></a>`timezone` | [`String!`](#string) | Time zone of the on-call schedule. |
 

ee/app/graphql/resolvers/incident_management/escalation_policies_resolver.rb

@@ -18,6 +18,8 @@ module Resolvers
       end
 
       def resolve_with_lookahead(**args)
+        context[:execution_time] = Time.current
+
         apply_lookahead(::IncidentManagement::EscalationPoliciesFinder.new(current_user, project, args).execute)
       end
 

ee/app/graphql/resolvers/incident_management/oncall_users_resolver.rb

@@ -8,7 +8,9 @@ module Resolvers
       type [::Types::UserType], null: true
 
       def resolve
-        ::IncidentManagement::OncallUsersFinder.new(schedule.project, schedule: schedule).execute
+        oncall_at = context[:execution_time] || Time.current
+
+        ::IncidentManagement::OncallUsersFinder.new(schedule.project, schedule: schedule, oncall_at: oncall_at).execute
       end
     end
   end

ee/app/graphql/types/incident_management/oncall_schedule_type.rb

@@ -41,7 +41,7 @@ module Types
 
       field :oncall_users,
             [::Types::UserType],
-            null: false,
+            null: true,
             resolver: ::Resolvers::IncidentManagement::OncallUsersResolver
     end
   end

ee/spec/graphql/resolvers/incident_management/oncall_users_resolver_spec.rb

@@ -24,6 +24,17 @@ RSpec.describe Resolvers::IncidentManagement::OncallUsersResolver do
     expect(schedule.participants.pluck(:user_id)).to include(users.first.id)
   end
 
+  it 'calls the finder with the execution_time context' do
+    execution_time = Time.current
+    context = { current_user: current_user, execution_time: execution_time }
+
+    expect(::IncidentManagement::OncallUsersFinder).to receive(:new)
+      .with(project, hash_including(oncall_at: execution_time))
+      .and_call_original
+
+    resolve_oncall_users({}, context)
+  end
+
   context 'when an error occurs while finding shifts' do
     before do
       stub_licensed_features(oncall_schedules: false)