syntax_data: {"ast_node_type":"other","tokens":[{"end":79,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// Record the fact that we need to serialize the corresponding `ExpnData`.
context_before: impl HygieneEncodeContext {
context_after:     pub fn schedule_expn_data_for_encoding(&self, expn: ExpnId) {