compile fail when HRTB + const trait

[loynoir]

I tried this code:

pub mod reproduce {
    #[const_trait]
    pub trait ConstFrom<T>: Sized {
        #[must_use]
        fn const_from(value: T) -> Self;
    }

    #[const_trait]
    pub trait ConstAddAssign<Rhs = Self> {
        fn const_add_assign(&mut self, rhs: Rhs);
    }

    pub fn incr42<T>(mut x: T)
    where
        T: const ConstFrom<u8> + for<'a> ConstAddAssign<&'a T>,
    {
        let delta = T::const_from(42u8);

        x.const_add_assign(&delta)
    }

    // fail to compile
    pub const fn const_incr42<T>(mut x: T)
    where
        T: ~const ConstFrom<u8> + for<'a> ~const ConstAddAssign<&'a T>,
    {
        let delta = T::const_from(42u8);

        x.const_add_assign(&delta)
    }
}

I expected to see this happen: compile OK when HRTB + const trait

Instead, this happened: compile fail when HRTB + const trait

Meta

rustc --version --verbose:

rustc 1.87.0-nightly (3ea711f17 2025-03-09)
binary: rustc
commit-hash: 3ea711f17e3946ac3f4df11691584e2c56b4b0cf
commit-date: 2025-03-09
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

Backtrace

<backtrace>

Related

Prev

#67792 (comment)

[fmease]

Thanks for opening an issue. However, as I also wrote in #67792 (comment), for now you just need to add T: ~const Destruct: Playground.

So this works as intended atm. In the future, whether, when & where you need to write ~cons Destruct may change. See rust-lang/rfcs#3762.