syntax_data: {"ast_node_type":"other","tokens":[{"end":42,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                 // implies unreachability.
context_before:                 // A never pattern is only allowed on an uninhabited type, so validity of the data
context_after:                 self.cfg.terminate(block, source_info, TerminatorKind::Unreachable);