syntax_data: {"ast_node_type":"other","tokens":[{"end":96,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:     // `SourceMap::lookup_source_file_idx` and `SourceFile::contains` both consider the position
context_before: fn file_contains(file: &SourceFile, pos: BytePos) -> bool {
context_after:     // one past the end of a file to belong to it. Normally, that's what we want. But for the