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

error: aborting due to previous error