Attributes for Param, SelfParam, and StructField types

[ambiguousname]

Per rust-lang/rust#60406 and https://doc.rust-lang.org/reference/attributes.html, attributes can be positioned in struct fields or parameters positions. Diplomat currently does not have an attrs field for the Param, ParamSelf, or StructField types.

This is something that would be especially nice to have for #500.

So for instance, you'd be able to write something like

struct SomeStruct {
  #[diplomat::attr(not(dart), disable)]
  pub dart_specific_feature,
}

Or

fn foo(
  #[diplomat::attr(kotlin, rename="someNewNameHere")]
  in : i32
) {}

[Manishearth]

How would disabling a struct field work? Renaming, sure, but I can't see how disabling would work.

But yes, we should support this. Figuring out the inheritance might be tricky.

[ambiguousname]

Disable was something of a random example, for a more specific use case for #500, the current attribute syntax looks something like this:

impl ICU4XLocale {
        /// Construct an [`ICU4XLocale`] from a locale identifier represented as a string.
        #[diplomat::attr(supports = constructors, constructor)]
        #[diplomat::demo(input(name(label = "Locale Name")))]
        pub fn new(name: &DiplomatStr) -> Box<ICU4XLocale> {
            Box::new(ICU4XLocale(Locale::try_from_bytes(name).unwrap()))
        }
    }

Could avoid a lot more boilerplate with this:

impl ICU4XLocale {
        /// Construct an [`ICU4XLocale`] from a locale identifier represented as a string.
        #[diplomat::attr(supports = constructors, constructor)]
        pub fn new(
        #[diplomat::demo(label = "Locale Name")]
        name: &DiplomatStr) -> Box<ICU4XLocale> {
            Box::new(ICU4XLocale(Locale::try_from_bytes(name).unwrap()))
        }
    }

[Manishearth]

Ah, yes, that would be fine. Some thought needs to be given to inheritance, I'd assume that most attributes do not inherit past this boundary

[Manishearth]

Shouldn't be hard to add support for if you're thinking of doing it!