error[E0277]: `T` cannot be shared between threads safely
  --> $DIR/phantom-auto-trait.rs:21:12
   |
LL |     is_zen(x)
   |     ------ ^ `T` cannot be shared between threads safely
   |     |
   |     required by a bound introduced by this call
   |
note: required for `&T` to implement `Zen`
  --> $DIR/phantom-auto-trait.rs:10:24
   |
LL | unsafe impl<'a, T: 'a> Zen for &'a T where T: Sync {}
   |                        ^^^     ^^^^^          ---- unsatisfied trait bound introduced here
   = note: required because it appears within the type `PhantomData<&T>`
note: required because it appears within the type `Guard<'_, T>`
  --> $DIR/phantom-auto-trait.rs:12:8
   |
LL | struct Guard<'a, T: 'a> {
   |        ^^^^^
note: required by a bound in `is_zen`
  --> $DIR/phantom-auto-trait.rs:18:14
   |
LL | fn is_zen<T: Zen>(_: T) {}
   |              ^^^ required by this bound in `is_zen`
help: consider restricting type parameter `T`
   |
LL | fn not_sync<T: std::marker::Sync>(x: Guard<T>) {
   |              +++++++++++++++++++

error[E0277]: `T` cannot be shared between threads safely
  --> $DIR/phantom-auto-trait.rs:26:12
   |
LL |     is_zen(x)
   |     ------ ^ `T` cannot be shared between threads safely
   |     |
   |     required by a bound introduced by this call
   |
note: required for `&T` to implement `Zen`
  --> $DIR/phantom-auto-trait.rs:10:24
   |
LL | unsafe impl<'a, T: 'a> Zen for &'a T where T: Sync {}
   |                        ^^^     ^^^^^          ---- unsatisfied trait bound introduced here
   = note: required because it appears within the type `PhantomData<&T>`
note: required because it appears within the type `Guard<'_, T>`
  --> $DIR/phantom-auto-trait.rs:12:8
   |
LL | struct Guard<'a, T: 'a> {
   |        ^^^^^
note: required because it appears within the type `Nested<Guard<'_, T>>`
  --> $DIR/phantom-auto-trait.rs:16:8
   |
LL | struct Nested<T>(T);
   |        ^^^^^^
note: required by a bound in `is_zen`
  --> $DIR/phantom-auto-trait.rs:18:14
   |
LL | fn is_zen<T: Zen>(_: T) {}
   |              ^^^ required by this bound in `is_zen`
help: consider restricting type parameter `T`
   |
LL | fn nested_not_sync<T: std::marker::Sync>(x: Nested<Guard<T>>) {
   |                     +++++++++++++++++++

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0277`.