syntax_data: {"ast_node_type":"other","tokens":[{"end":64,"kind":"keyword","start":0,"text":".chain(iter::once(((a.output(),"}]}
source_snippet:             .chain(iter::once(((a.output(), b.output()), true)))
context_before:             .map(|(a, b)| ((a, b), false))
context_after:             .map(|((a, b), is_output)| {