error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults --> $DIR/issue-83929-impl-trait-in-generic-default.rs:1:16 | LL | struct Foo(T); | ^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults --> $DIR/issue-83929-impl-trait-in-generic-default.rs:4:20 | LL | type Result = std::result::Result; | ^^^^^^^^^^^^^^^^^^^^^^ error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0562`.