facet - size_of in const context

Cargo.toml

[package]
name = "facet-size-test"
version = "0.1.0"
edition = "2024"

[dependencies]
facet = { version = "0.27.6", default-features = false }

main.rs

// #![no_std]

#[derive(facet::Facet)]
struct Foobar {
    foo: u32,
    bar: u64,
}

const fn size_of<'a, T: facet::Facet<'a>>() -> usize {
    let facet::ShapeLayout::Sized(layout) = T::SHAPE.layout else {
        panic!("type is unsized");
    };

    layout.size()
}

fn main() {
    let buf: [u8; size_of::<Foobar>()] = [0; size_of::<Foobar>()];
    println!("buf is {} bytes", buf.len());
}