syntax_data: {"ast_node_type":"other","tokens":[{"end":72,"kind":"keyword","start":0,"text":".expect(\"expected"}]}
source_snippet:                     .expect("expected len of array pat to be definite");
context_before:                     .try_to_target_usize(self.tcx)
context_after:                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);