error: implementing `rustc_specialization_trait` traits is unstable
  --> $DIR/impl_specialization_trait.rs:11:1
   |
LL | impl specialization_trait::SpecTrait for A {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add `#![feature(min_specialization)]` to the crate attributes to enable

error: aborting due to previous error