{"ast_node_type":"variable","tokens":[{"end":68,"kind":"keyword","start":0,"text":"let"}]}
        let mut self_ty = self.tcx.peel_off_free_alias_tys(self_ty);
        let self_ty = self.tcx.type_of(id).instantiate_identity();
        // We allow impls on pattern types exactly when we allow impls on the base type.