error[E0271]: type mismatch resolving `<Result<..., ()> as Future>::Error == Foo`
   ╭▸ $DIR/E0271.rs:19:5
   │
LL │ ┏     Box::new(
LL │ ┃         Ok::<_, ()>(
LL │ ┃             Err::<(), _>(
LL │ ┃                 Ok::<_, ()>(
   ‡ ┃
LL │ ┃     )
   │ ┗━━━━━┛ type mismatch resolving `<Result<..., ()> as Future>::Error == Foo`
   ╰╴
note: expected this to be `Foo`
   ╭▸ $DIR/E0271.rs:9:18
   │
LL │     type Error = E;
   │                  ━
   ├ note: required for the cast from `Box<Result<..., ()>>` to `Box<...>`
   ├ note: the full name for the type has been written to '$TEST_BUILD_DIR/E0271.long-type-$LONG_TYPE_HASH.txt'
   ╰ note: consider using `--verbose` to print the full type name to the console

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0271`.