syntax_data: {"ast_node_type":"other","tokens":[{"end":23,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// and destructor.
context_before:     /// have a "trivial" vtable consisting of just the size, alignment,
context_after:     pub fn principal(&self) -> Option<ty::Binder<'tcx, ExistentialTraitRef<'tcx>>> {