syntax_data: {"ast_node_type":"function","tokens":[{"end":88,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn check_let(&mut self, pat: &'p Pat<'tcx>, scrutinee: Option<ExprId>, span: Span) {
context_before:     #[instrument(level = "trace", skip(self))]
context_after:         assert!(self.let_source != LetSource::None);