`const` code depending on `TypeId` throws mismatched type error

[cafce25]

I tried to create a function that statically computes if two type parameters are the same:

#![feature(const_type_id, const_trait_impl, effects)]
use std::any::TypeId;
const fn same_type<T1, T2>() -> bool {
    TypeId::of::<T1>() == TypeId::of::<T2>()
}

Depending on whether the type of T1 and T2 is the same the function should be able to produce true or false at compile time.

Instead, the compiler throws the following error:

error[E0308]: mismatched types
 --> src/lib.rs:4:5
  |
4 |     TypeId::of::<T1>() == TypeId::of::<T2>()
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `host`, found `true`
  |
  = note: expected constant `host`
             found constant `true`

Meta

rustc --version:

1.80.0-nightly (2024-05-04 e82c861d7e5ecd766cb0)

[asquared31415]

@rustbot label +T-compiler +F-effects -needs-triage

[bjorn3]

The PartialEq impl for TypeId is not marked as const and as such can't be used in const contexts. const_type_id only enables creating a TypeId in const contexts, not comparing it.