Implicit trait implementation do not work

[SwayStar123]

Minimum reproduction:

contract;

use std::convert::*;
use std::primitive_conversions::u64::*;

abi MyContract {
    fn test_function() -> bool;
}

impl MyContract for Contract {
    fn test_function() -> bool {
        true
    }
}

pub struct MyStruct {
    inner_val: u64,
}

impl MyStruct {
    pub fn new<T>(val: T) -> Self
    where T: Into<u64> {
        MyStruct { inner_val: val.into() }
    }
}

#[test]
fn test_method() {
    let s1 = MyStruct::new(1u8);

    assert(s1.inner_val == 1);
}

Despite impl From<u8> for u64 existing, and

impl<T, U> Into<U> for T
where
    U: From<T>,
{

existing, the compiler errors with
^^^^^^^^^^^^ Trait "Into<u64>" is not implemented for type "u8".