Specialization hack might stop working in future rust versions.

[theemathas]

Currently, this code relies on the fact that std uses specialization for cloning arrays. This is an implementation detail, and is not supported.

LibAFL/libafl_bolts/src/tuples.rs

Lines 23 to 54 in 0573bbb

	/// Returns if the type `T` is equal to `U`, ignoring lifetimes.
	#[inline] // this entire call gets optimized away :)
	#[must_use]
	pub fn type_eq<T: ?Sized, U: ?Sized>() -> bool {
	// decider struct: hold a cell (which we will update if the types are unequal) and some
	// phantom data using a function pointer to allow for Copy to be implemented
	struct W<'a, T: ?Sized, U: ?Sized>(&'a Cell<bool>, PhantomData<fn() -> (&'a T, &'a U)>);
	// default implementation: if the types are unequal, we will use the clone implementation
	impl<T: ?Sized, U: ?Sized> Clone for W<'_, T, U> {
	#[inline]
	fn clone(&self) -> Self {
	// indicate that the types are unequal
	// unfortunately, use of interior mutability (Cell) makes this not const-compatible
	// not really possible to get around at this time
	self.0.set(false);
	W(self.0, self.1)
	}
	}
	// specialized implementation: Copy is only implemented if the types are the same
	#[expect(clippy::mismatching_type_param_order)]
	impl<T: ?Sized> Copy for W<'_, T, T> {}
	let detected = Cell::new(true);
	// [].clone() is *specialized* in core.
	// Types which implement copy will have their copy implementations used, falling back to clone.
	// If the types are the same, then our clone implementation (which sets our Cell to false)
	// will never be called, meaning that our Cell's content remains true.
	let res = [W::<T, U>(&detected, PhantomData)].clone();
	res[0].0.get()
	}

In a future version of rust, this specialization might be removed, breaking this code. See rust-lang/rust#135634 and rust-lang/rust#132442

Maybe consider using the typeid crate instead.

[addisoncrump]

Hey, thanks for pointing to typeid. We've needed a proper replacement for this hack for some time, I'll see if I can't migrate to this.