syntax_data: {"ast_node_type":"other","tokens":[{"end":65,"kind":"keyword","start":0,"text":"\"future-incompat\""}]}
source_snippet:                 "future-incompat" => json_future_incompat = true,
context_before:                 "unused-externs-silent" => json_unused_externs = JsonUnusedExterns::Silent,
context_after:                 s => early_dcx.early_fatal(format!("unknown `--json` option `{s}`")),