error[E0091]: type parameter `T` is unused --> $DIR/E0091.rs:11:10 | LL | type Foo = u32; //~ ERROR E0091 | ^ unused type parameter error[E0091]: type parameter `B` is unused --> $DIR/E0091.rs:12:14 | LL | type Foo2 = Box; //~ ERROR E0091 | ^ unused type parameter error: aborting due to 2 previous errors If you want more information on this error, try using "rustc --explain E0091"