error: unconstrained opaque type
  --> $DIR/unnameable_type.rs:17:18
   |
LL | type MyPrivate = impl Sized;
   |                  ^^^^^^^^^^
   |
   = note: `MyPrivate` must be used in combination with a concrete type within the same module

error[E0053]: method `dont_define_this` has an incompatible type for trait
  --> $DIR/unnameable_type.rs:20:35
   |
LL | type MyPrivate = impl Sized;
   |                  ---------- the found opaque type
...
LL |     fn dont_define_this(_private: MyPrivate) {}
   |                                   ^^^^^^^^^
   |                                   |
   |                                   expected `Private`, found opaque type
   |                                   help: change the parameter type to match the trait: `Private`
   |
note: type in trait
  --> $DIR/unnameable_type.rs:10:39
   |
LL |         fn dont_define_this(_private: Private) {}
   |                                       ^^^^^^^
   = note: expected signature `fn(Private)`
              found signature `fn(MyPrivate)`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0053`.