{"ast_node_type":"function","tokens":[{"end":52,"kind":"keyword","start":0,"text":"pub"}]}
    pub fn expect_region(self) -> ty::Region<'tcx> {
    /// Unpack the `GenericArg` as a region when it is known certainly to be a region.
        self.as_region().unwrap_or_else(|| bug!("expected a region, but found another kind"))