syntax_data: {"ast_node_type":"other","tokens":[{"end":72,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:     // after a cache miss will produce the last line number, as desired.
context_before:     // misses for these rare positions. A line lookup for the position via `SourceMap::lookup_line`
context_after:     line: Range<BytePos>,