error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
  --> $DIR/issue-67535.rs:3:1
   |
LL | impl std::ops::AddAssign for () {
   | ^^^^^-------------------^^^^^--
   | |    |                       |
   | |    |                       this is not defined in the current crate because tuples are always foreign
   | |    this is not defined in the current crate because this is a foreign trait
   | impl doesn't use only types from inside the current crate
   |
   = note: define and implement a trait or new type instead

error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
  --> $DIR/issue-67535.rs:10:1
   |
LL | impl std::ops::AddAssign for [(); 1] {
   | ^^^^^-------------------^^^^^-------
   | |    |                       |
   | |    |                       this is not defined in the current crate because arrays are always foreign
   | |    this is not defined in the current crate because this is a foreign trait
   | impl doesn't use only types from inside the current crate
   |
   = note: define and implement a trait or new type instead

error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
  --> $DIR/issue-67535.rs:17:1
   |
LL | impl std::ops::AddAssign for &[u8] {
   | ^^^^^-------------------^^^^^-----
   | |    |                       |
   | |    |                       this is not defined in the current crate because slices are always foreign
   | |    this is not defined in the current crate because this is a foreign trait
   | impl doesn't use only types from inside the current crate
   |
   = note: define and implement a trait or new type instead

error[E0053]: method `add_assign` has an incompatible type for trait
  --> $DIR/issue-67535.rs:5:19
   |
LL |     fn add_assign(&self, other: ()) -> () {
   |                   ^^^^^
   |                   |
   |                   types differ in mutability
   |                   help: change the self-receiver type to match the trait: `&mut self`
   |
   = note: expected signature `fn(&mut (), ())`
              found signature `fn(&(), ())`

error[E0053]: method `add_assign` has an incompatible type for trait
  --> $DIR/issue-67535.rs:12:19
   |
LL |     fn add_assign(&self, other: [(); 1]) -> [(); 1] {
   |                   ^^^^^
   |                   |
   |                   types differ in mutability
   |                   help: change the self-receiver type to match the trait: `&mut self`
   |
   = note: expected signature `fn(&mut _, _)`
              found signature `fn(&_, _) -> [(); 1]`

error[E0053]: method `add_assign` has an incompatible type for trait
  --> $DIR/issue-67535.rs:19:19
   |
LL |     fn add_assign(&self, other: &[u8]) -> &[u8] {
   |                   ^^^^^
   |                   |
   |                   types differ in mutability
   |                   help: change the self-receiver type to match the trait: `&mut self`
   |
   = note: expected signature `fn(&mut &_, &_)`
              found signature `fn(&&_, &_) -> &[u8]`

error: aborting due to 6 previous errors

Some errors have detailed explanations: E0053, E0117.
For more information about an error, try `rustc --explain E0053`.