error[E0283]: type annotations needed
  --> $DIR/auto-trait-selection.rs:15:16
   |
LL |     if false { is_trait(foo()) } else { Default::default() }
   |                ^^^^^^^^ cannot infer type of the type parameter `U` declared on the function `is_trait`
   |
note: multiple `impl`s satisfying `impl Sized: Trait<_>` found
  --> $DIR/auto-trait-selection.rs:12:1
   |
LL | impl<T: Send> Trait<u32> for T {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL | impl<T> Trait<i32> for T {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `is_trait`
  --> $DIR/auto-trait-selection.rs:7:16
   |
LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
   |                ^^^^^^^^ required by this bound in `is_trait`
help: consider specifying the generic arguments
   |
LL |     if false { is_trait::<_, U>(foo()) } else { Default::default() }
   |                        ++++++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0283`.