syntax_data: {"ast_node_type":"import","tokens":[{"end":77,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:     // is unstable, it will not be present. We have to use `opts_present` not
context_before:     // with only stable options if no unstable options are used. Since error-format
context_after:     // `opt_present` because the latter will panic.