We want to include the name of a document's containing document library in search results, but it doesn't appear to be a managed or crawled property. Is there a way to achieve this without custom code to set the value of a hidden field on every document to be the value of its document library's name?
The Document Library name is not included when the document is indexed. The best you could do is return the SitePath, which, despite the name, is the path to the library.
If you wanted to, you could make a REST call and get the Library Name from the SitePath property inside your Display Template.