Merge branch 'fix-create-mr-from-issue-with-template' into 'master'

app/services/issuable_base_service.rb

@@ -106,12 +106,14 @@ class IssuableBaseService < BaseService
   end
 
   def merge_quick_actions_into_params!(issuable)
+    original_description = params.fetch(:description, issuable.description)
+
     description, command_params =
       QuickActions::InterpretService.new(project, current_user)
-        .execute(params[:description], issuable)
+        .execute(original_description, issuable)
 
     # Avoid a description already set on an issuable to be overwritten by a nil
-    params[:description] = description if params.key?(:description)
+    params[:description] = description if description
 
     params.merge!(command_params)
   end

changelogs/unreleased/fix-create-mr-from-issue-with-template.yml

+---
+title: Execute quick actions (if present) when creating MR from issue
+merge_request: 15810
+author:
+type: fixed

spec/services/merge_requests/create_from_issue_service_spec.rb

@@ -100,5 +100,17 @@ describe MergeRequests::CreateFromIssueService do
 
       expect(result[:merge_request].target_branch).to eq(project.default_branch)
     end
+
+    it 'executes quick actions if the build service sets them in the description' do
+      allow(service).to receive(:merge_request).and_wrap_original do |m, *args|
+        m.call(*args).tap do |merge_request|
+          merge_request.description = "/assign #{user.to_reference}"
+        end
+      end
+
+      result = service.execute
+
+      expect(result[:merge_request].assignee).to eq(user)
+    end
   end
 end