syntax_data: {"ast_node_type":"function","tokens":[{"end":57,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn decode_syntax_context(&mut self) -> SyntaxContext;
context_before:     fn decode_expn_id(&mut self) -> ExpnId;
context_after:     fn decode_crate_num(&mut self) -> CrateNum;