Fix creating epics with dates from api

- set start_date and end_date if dates are fixed

changelogs/unreleased/13360-fix-epics-api.yml

+---
+title: Fix creating epics with dates from api
+merge_request: 18393
+author:
+type: fixed

ee/app/services/epics/create_service.rb

@@ -20,7 +20,17 @@ module Epics
     end
 
     def whitelisted_epic_params
-      params.slice(:title, :description, :start_date, :end_date, :milestone, :label_ids, :parent_id)
+      result = params.slice(:title, :description, :label_ids, :parent_id)
+
+      if params[:start_date_fixed] && params[:start_date_is_fixed]
+        result[:start_date] = params[:start_date_fixed]
+      end
+
+      if params[:due_date_fixed] && params[:due_date_is_fixed]
+        result[:end_date] = params[:due_date_fixed]
+      end
+
+      result
     end
   end
 end

ee/spec/requests/api/epics_spec.rb

@@ -491,6 +491,7 @@ describe API::Epics do
           expect(epic.description).to eq('epic description')
           expect(epic.start_date_fixed).to eq(nil)
           expect(epic.start_date_is_fixed).to be_falsey
+          expect(epic.due_date).to eq(Date.new(2018, 7, 17))
           expect(epic.due_date_fixed).to eq(Date.new(2018, 7, 17))
           expect(epic.due_date_is_fixed).to eq(true)
           expect(epic.labels.first.title).to eq('label1')

ee/spec/services/epics/create_service_spec.rb

@@ -25,4 +25,19 @@ describe Epics::CreateService do
       expect(NewEpicWorker).to have_received(:perform_async).with(epic.id, user.id)
     end
   end
+
+  context 'handling fixed dates' do
+    it 'sets the fixed date correctly' do
+      date = Date.new(2019, 10, 10)
+      params[:start_date_fixed] = date
+      params[:start_date_is_fixed] = true
+
+      subject
+
+      epic = Epic.last
+      expect(epic.start_date).to eq(date)
+      expect(epic.start_date_fixed).to eq(date)
+      expect(epic.start_date_is_fixed).to be_truthy
+    end
+  end
 end