error: inherent impls cannot be default
  --> $DIR/validation.rs:7:14
   |
LL | default impl S {}
   | -------      ^ inherent impl for this type
   | |
   | default because of this
   |
   = note: only trait implementations may be annotated with `default`

warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
  --> $DIR/validation.rs:2:12
   |
LL | #![feature(specialization)]
   |            ^^^^^^^^^^^^^^
   |
   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
   = help: consider using `min_specialization` instead, which is more stable and complete
   = note: `#[warn(incomplete_features)]` on by default

error[E0367]: `!Send` impl requires `Z: Send` but the struct it is implemented for does not
  --> $DIR/validation.rs:12:1
   |
LL | default impl !Send for Z {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: the implementor must specify the same requirement
  --> $DIR/validation.rs:5:1
   |
LL | struct Z;
   | ^^^^^^^^

error: impls of auto traits cannot be default
  --> $DIR/validation.rs:9:21
   |
LL | default unsafe impl Send for S {}
   | -------             ^^^^ auto trait
   | |
   | default because of this

error: impls of auto traits cannot be default
  --> $DIR/validation.rs:12:15
   |
LL | default impl !Send for Z {}
   | -------       ^^^^ auto trait
   | |
   | default because of this

error[E0750]: negative impls cannot be default impls
  --> $DIR/validation.rs:12:1
   |
LL | default impl !Send for Z {}
   | ^^^^^^^      ^

error[E0750]: negative impls cannot be default impls
  --> $DIR/validation.rs:19:1
   |
LL | default impl !Tr for S {}
   | ^^^^^^^      ^

error: aborting due to 6 previous errors; 1 warning emitted

Some errors have detailed explanations: E0367, E0750.
For more information about an error, try `rustc --explain E0367`.