syntax_data: {"ast_node_type":"other","tokens":[{"end":80,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                         // to know whether to check lifetimes in their pointees,
context_before:                         // BorrowCk needed to track whether these cases were coercions or casts,
context_after:                         // but from now on that distinction doesn't matter,