syntax_data: {"ast_node_type":"variable","tokens":[{"end":71,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let new_ctxt = map(SyntaxContext::from_u16(span.ctxt));
context_before:                 // so it makes sense to micro-optimize it to avoid `span.data()` and `Span::new()`.
context_after:                 let new_ctxt32 = new_ctxt.as_u32();