syntax_data: {"ast_node_type":"other","tokens":[{"end":19,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// unmodified.
context_before:     /// If a file already exists in the `SourceMap` with the same ID, that file is returned
context_after:     pub fn new_source_file(&self, filename: FileName, src: String) -> Arc<SourceFile> {