error[E0107]: missing generics for associated type `SuperTrait::SubType`
  --> $DIR/issue-76535.rs:39:33
   |
LL |     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
   |                                 ^^^^^^^ expected 1 lifetime argument
   |
note: associated type defined here, with 1 lifetime parameter: `'a`
  --> $DIR/issue-76535.rs:9:10
   |
LL |     type SubType<'a>: SubTrait where Self: 'a;
   |          ^^^^^^^ --
help: add missing lifetime argument
   |
LL |     let sub: Box<dyn SuperTrait<SubType<'a> = SubStruct>> = Box::new(SuperStruct::new(0));
   |                                 ~~~~~~~~~~~

error[E0038]: the trait `SuperTrait` cannot be made into an object
  --> $DIR/issue-76535.rs:39:14
   |
LL |     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `SuperTrait` cannot be made into an object
   |
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> $DIR/issue-76535.rs:9:10
   |
LL | pub trait SuperTrait {
   |           ---------- this trait cannot be made into an object...
LL |     type SubType<'a>: SubTrait where Self: 'a;
   |          ^^^^^^^ ...because it contains the generic associated type `SubType`
   = help: consider moving `SubType` to another trait

error[E0038]: the trait `SuperTrait` cannot be made into an object
  --> $DIR/issue-76535.rs:39:57
   |
LL |     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
   |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `SuperTrait` cannot be made into an object
   |
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> $DIR/issue-76535.rs:9:10
   |
LL | pub trait SuperTrait {
   |           ---------- this trait cannot be made into an object...
LL |     type SubType<'a>: SubTrait where Self: 'a;
   |          ^^^^^^^ ...because it contains the generic associated type `SubType`
   = help: consider moving `SubType` to another trait
   = note: required for `Box<SuperStruct>` to implement `CoerceUnsized<Box<dyn SuperTrait<SubType = SubStruct<'_>>>>`
   = note: required by cast to type `Box<dyn SuperTrait<SubType = SubStruct<'_>>>`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0038, E0107.
For more information about an error, try `rustc --explain E0038`.