min_specialization with const traits can call non-const function in consteval

[theemathas]

#![feature(min_specialization, const_trait_impl)]

struct Dummy;

const trait One {
    fn one();
}
impl One for Dummy {
    fn one() {
        println!("wut");
    }
}

const trait Two {
    fn two();
}
impl<T: One, U> const Two for (T, U) {
    default fn two() {
        unreachable!();
    }
}
impl<T: [const] One> const Two for (T, i32) {
    fn two() {
        T::one();
    }
}

const trait Three {
    fn three();
}
impl<T: One, U> const Three for (T, U) {
    fn three() {
        <(T, U)>::two();
    }
}

const A: () = {
    <(Dummy, i32)>::three();
};

fn main() {}

error[E0080]: calling non-const function `<Dummy as One>::one`
  --> src/main.rs:38:5
   |
38 |     <(Dummy, i32)>::three();
   |     ^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `A` failed inside this call
   |
note: inside `<(Dummy, i32) as Three>::three`
  --> src/main.rs:33:9
   |
33 |         <(T, U)>::two();
   |         ^^^^^^^^^^^^^^^
note: inside `<(Dummy, i32) as Two>::two`
  --> src/main.rs:24:9
   |
24 |         T::one();
   |         ^^^^^^^^ the failure occurred here

For more information about this error, try `rustc --explain E0080`.

This code manages to get through const checking without any errors, and only produces an error while "executing" consteval and running into the non-const function. This seems incorrect. The compiler is supposed to disallow calling non-const functions in consteval before actually running consteval.

Meta

Reproducible on the playground with version 1.93.0-nightly (2025-10-27 adaa838976ff99a4f066)

[theemathas]

Slightly simplified:

#![feature(min_specialization, const_trait_impl)]

struct Dummy;

const trait DummyTrait {
    fn dummy_fn();
}
impl DummyTrait for Dummy {
    fn dummy_fn() {
        println!("wut");
    }
}

const trait Trait {
    fn trait_fn();
}
impl<T> const Trait for T {
    default fn trait_fn() {
        unreachable!();
    }
}
impl const Trait for i32 where Dummy: [const] DummyTrait {
    fn trait_fn() {
        Dummy::dummy_fn();
    }
}

const fn indirect<T>() {
    T::trait_fn();
}

const A: () = {
    indirect::<i32>();
};

fn main() {}

error[E0080]: calling non-const function `<Dummy as DummyTrait>::dummy_fn`
  --> src/main.rs:33:5
   |
33 |     indirect::<i32>();
   |     ^^^^^^^^^^^^^^^^^ evaluation of `A` failed inside this call
   |
note: inside `indirect::<i32>`
  --> src/main.rs:29:5
   |
29 |     T::trait_fn();
   |     ^^^^^^^^^^^^^
note: inside `<i32 as Trait>::trait_fn`
  --> src/main.rs:24:9
   |
24 |         Dummy::dummy_fn();
   |         ^^^^^^^^^^^^^^^^^ the failure occurred here

For more information about this error, try `rustc --explain E0080`.