Optional attribute on field?

[romamik]

Let's say I have a struct:

struct Foo {
   // no attribute at all
   a: i32

   #[my_attr(some_param=100, other_param=200)]
   b: i32
}

// in macro
#[derive(Debug, Clone, deluxe::ParseAttributes)]
#[deluxe(attributes=["my_attr"])]
struct FieldAttr {
  // no default values
  some_param: i32
  other_param: i32
}

But I'd like to parse Option<FieldAttr> to allow fields with no my_attr at all.

[romamik]

I ended up with this monstrosity which I consider a temporary solution:

// usage: deluxe::parse_attributes::<Field, OptionalAttr<FieldAttr>>(field)

#[derive(Debug, Clone)]
pub struct OptionalAttr<R>(pub Option<R>);

impl<'t, R> ParseAttributes<'t, Field> for OptionalAttr<R>
where
    R: ParseAttributes<'t, Field>,
{
    fn path_matches(path: &syn::Path) -> bool {
        R::path_matches(path)
    }

    fn parse_attributes(src: &'t Field) -> Result<Self> {
        let has_attr = src
            .attrs()
            .iter()
            .any(|attr| Self::path_matches(attr.path()));

        Ok(if has_attr {
            Self(Some(R::parse_attributes(src)?))
        } else {
            Self(None)
        })
    }
}