syntax_data: {"ast_node_type":"other","tokens":[{"end":70,"kind":"keyword","start":0,"text":"encode_expn(encoder,"}]}
source_snippet:                     encode_expn(encoder, expn, &expn_data, expn_hash);
context_before:                 if self.serialized_expns.lock().insert(expn) {
context_after:                 }