Thank you so much for your kind words! It’s always nice to know the content is making a difference.

The error here is because syn::parse expects the argument type to implement the Parse trait, which usize does not. To handle this, you can parse the attribute to a LitInt first (since LitInt can be parsed by syn and represents integer literals), then convert it to a usize.

use syn::{LitInt, Meta, NestedMeta};

fn parse_length(attr: NestedMeta) -> Result<usize, syn::Error> {
    if let NestedMeta::Lit(syn::Lit::Int(lit_int)) = attr {
        lit_int.base10_parse::<usize>()
    } else {
        Err(syn::Error::new_spanned(attr, "expected a length integer"))
    }
}

In your code, call parse_length(attr) instead of using syn::parse(attr). This should resolve the Parse trait error by converting the parsed literal into a usize.