syntax_data: {"ast_node_type":"other","tokens":[{"end":22,"kind":"keyword","start":0,"text":"tcx:"}]}
source_snippet:     tcx: TyCtxt<'tcx>,
context_before: pub(super) fn vtable_allocation_provider<'tcx>(
context_after:     key: (Ty<'tcx>, Option<ty::ExistentialTraitRef<'tcx>>),