error: This generic shadows the built-in type `u32`
 --> $DIR/builtin-type-shadow.rs:5:8
  |
5 | fn foo<u32>(a: u32) -> u32 {
  |        ^^^
  |
  = note: `-D builtin-type-shadow` implied by `-D warnings`

error[E0308]: mismatched types
 --> $DIR/builtin-type-shadow.rs:6:5
  |
5 | fn foo<u32>(a: u32) -> u32 {
  |                        --- expected `u32` because of return type
6 |     42
  |     ^^ expected type parameter, found integral variable
  |
  = note: expected type `u32`
             found type `{integer}`

error: aborting due to 2 previous errors

If you want more information on this error, try using "rustc --explain E0308"