warning: trait aliases are experimental
  --> $DIR/cfg-false-feature.rs:14:1
   |
LL | trait A = Clone;
   | ^^^^^^^^^^^^^^^^
   |
   = note: see issue #41517 <https://github.com/rust-lang/rust/issues/41517> for more information
   = help: add `#![feature(trait_alias)]` to the crate attributes to enable
   = warning: unstable syntax can change at any point in the future, causing a hard error!
   = note: for more information, see issue #65860 <https://github.com/rust-lang/rust/issues/65860>

warning: `macro` is experimental
  --> $DIR/cfg-false-feature.rs:11:1
   |
LL | macro mac() {}
   | ^^^^^^^^^^^^^^
   |
   = note: see issue #39412 <https://github.com/rust-lang/rust/issues/39412> for more information
   = help: add `#![feature(decl_macro)]` to the crate attributes to enable
   = warning: unstable syntax can change at any point in the future, causing a hard error!
   = note: for more information, see issue #65860 <https://github.com/rust-lang/rust/issues/65860>

warning: box pattern syntax is experimental
  --> $DIR/cfg-false-feature.rs:18:9
   |
LL |     let box _ = Box::new(0);
   |         ^^^^^
   |
   = note: see issue #29641 <https://github.com/rust-lang/rust/issues/29641> for more information
   = help: add `#![feature(box_patterns)]` to the crate attributes to enable
   = warning: unstable syntax can change at any point in the future, causing a hard error!
   = note: for more information, see issue #65860 <https://github.com/rust-lang/rust/issues/65860>

warning: 3 warnings emitted