Clippy build fails because the feature `result_map_or` has been
stabilized in v1.41.0 but we still have an explicit feature
attribute for it.
#![cfg_attr(feature = "deny-warnings", deny(warnings))]
#![feature(crate_visibility_modifier)]
#![feature(concat_idents)]
-#![feature(result_map_or)]
// FIXME: switch to something more ergonomic here, once available.
// (Currently there is no way to opt into sysroot crates without `extern crate`.)
#![cfg_attr(feature = "deny-warnings", deny(warnings))]
-#![feature(result_map_or)]
#![feature(rustc_private)]
// FIXME: switch to something more ergonomic here, once available.