syntax_data: {"ast_node_type":"other","tokens":[{"end":65,"kind":"keyword","start":0,"text":"BorrowKind::Mut"}]}
source_snippet:                 BorrowKind::Mut { kind: MutBorrowKind::Default },
context_before:                 tcx.lifetimes.re_erased,
context_after:                 fut_place,