Function rustdoc::passes::collect_intra_doc_links::resolve_associated_trait_item

fn resolve_associated_trait_item<'a>(
    ty: Ty<'a>,
    module: DefId,
    item_name: Symbol,
    ns: Namespace,
    cx: &mut DocContext<'a>
) -> Option<AssocItem>

Look to see if a resolved item has an associated item named item_name.

Given [std::io::Error::source], where source is unresolved, this would find std::error::Error::source and return <io::Error as error::Error>::source.