{"ast_node_type":"other","tokens":[{"end":52,"kind":"keyword","start":0,"text":"Custom(crate::error::CustomSubdiagnostic<'tcx>),"}]}
    Custom(crate::error::CustomSubdiagnostic<'tcx>),
    /// A custom (free-form) fluent-translated error, created by `err_ub_custom!`.
    /// Validation error.