syntax_data: {"ast_node_type":"variable","tokens":[{"end":60,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let span = Span::with_root_ctxt(BytePos(5), BytePos(5));
context_before:     // Reaching to the end of file, return a span that will get error with `span_to_snippet`
context_after:     let span = sm.next_point(span);