syntax_data: {"ast_node_type":"other","tokens":[{"end":68,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // FIXME(generic_const_exprs): We may want to support these.
context_before:         }
context_after:         ExprKind::RawBorrow { .. } | ExprKind::Deref { .. } => maybe_supported_error(