Request hover support for constants defined with `const fn`

[xpe]

I would like to ask for textDocument/hover support for constants defined with const fn. In my example below, you can see that an add function works, but not usize.ilog2().

Works as expected

pub const fn add(a: u32, b: u32) -> u32 { a + b }
pub const ADD_EXAMPLE: u32 = add(2, 3);

Hovering over ADD_EXAMPLE shows 5 as expected...

Feature request

pub const fn ilog2(n: u32) -> u32 { n.ilog2() }
pub const ILOG2_EXAMPLE: u32 = ilog2(16);

But hovering over ILOG2_EXAMPLE currently shows: ilog2(16) instead of 4...

Background

I have an application where I define constants based on usize.ilog2() and I like to sanity check the results in my editor.

[ChayimFriedman2]

We have a custom MIR lowering and evaluation. We show the value if we can evaluate the constant. I haven't looked where exactly we fail for ilog2(), but we just need to extend our supported set of operations for that. So this isn't really a feature request, more like an in-progress feature.