{"ast_node_type":"variable","tokens":[{"end":54,"kind":"keyword","start":0,"text":"let"}]}
    let sm = SourceMap::new(FilePathMapping::empty());
    // regression test for https://github.com/rust-lang/rust/issues/141665
    sm.new_source_file(PathBuf::from("foo.rs").into(), r#"#[doc = "⚠"] fn foo() {}"#.to_string());