src/test/ui/regions/regions-implied-bounds-projection-gap-1.rs

// Illustrates the "projection gap": in this test, even though we know
// that `T::Foo: 'x`, that does not tell us that `T: 'x`, because
// there might be other ways for the caller of `func` to show that
// `T::Foo: 'x` holds (e.g., where-clause).

trait Trait1<'x> {
    type Foo;
}

// calling this fn should trigger a check that the type argument
// supplied is well-formed.
fn wf<T>() { }

fn func<'x, T:Trait1<'x>>(t: &'x T::Foo)
{
    wf::<&'x T>();
    //~^ ERROR the parameter type `T` may not live long enough
}

fn caller2<'x, T:Trait1<'x>>(t: &'x T)
{
    wf::<&'x T::Foo>(); // OK
}

fn caller3<'x, T:Trait1<'x>>(t: &'x T::Foo)
{
    wf::<&'x T::Foo>(); // OK
}

fn main() { }