error[E0658]: the `#[default_lib_allocator]` attribute is an experimental feature
  --> $DIR/feature-gate-allocator_internals.rs:11:1
   |
LL | #![default_lib_allocator] //~ ERROR: attribute is an experimental feature
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add #![feature(allocator_internals)] to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.