syntax_data: {"ast_node_type":"function","tokens":[{"end":78,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn expr_error(&self, expr: ExprId, expected: &'static str) -> ParseError {
context_before: impl<'a, 'tcx> ParseCtxt<'a, 'tcx> {
context_after:         let expr = &self.thir[expr];