syntax_data: {"ast_node_type":"function","tokens":[{"end":73,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn mk_err(&self, mut err: Diag<'_>, ty: Ty<'tcx>) -> Box<Pat<'tcx>> {
context_before:     /// We errored. Signal that in the pattern, so that follow up errors can be silenced.
context_after:         if let ty::ConstKind::Unevaluated(uv) = self.c.kind() {