cyqsimon / documented Goto Github PK

I love the idea for this crate! Unfortunately when I tried to use it I ran into some trouble because the enum I wanted to apply DocumentedVariants to has a generic type parameter L:

#[derive(.., Clone, .., documented::DocumentedVariants)]
pub enum Instr<L> {
    /// Dispatch on the type of the value pointed to by `X1`.
    SwitchOnTerm { .. }
    // ..
}

The error I get says:

error[E0107]: missing generics for enum `Instr`
  --> src\bc\instr.rs:93:10
   |
93 | pub enum Instr<L> {
   |          ^^^^^ expected 1 generic argument
   |
note: enum defined here, with 1 generic parameter: `L`
  --> src\bc\instr.rs:93:10
   |
93 | pub enum Instr<L> {
   |          ^^^^^ -
help: add missing generic argument
   |
93 | pub enum Instr<L><L> {
   |               +++

I figured out a workaround though.

1. In my case I could assign the type () as a default for L:

   pub enum Instr<L = ()> {

2. Then I wrote a helper impl:

   impl<L: Clone> Instr<L> {
       pub fn doc_comment(&self) -> Option<&'static str> {
           let mapped: Instr<()> = self.clone().map_lbl(|_| ()); // Throw away `L`, make it `()`.
           documented::DocumentedVariants::get_variant_docs(&mapped).ok()
       }
   }

   Unfortunately this requires that L be Clone (still ok for my use case, but unsatisfying).

   Here map_lbl maps the L parameter to a new type. It's signature looks like this:

   impl<L> Instr<L> {
       pub fn map_lbl<M>(self, f: impl Fn(L) -> M) -> Instr<M> { .. }
   }

I'm not sure how the derive macro works, but it seems like handling generic type parameters just hasn't been implemented yet. Would this be easy to fix?

Hello, I want to use this to have comments on a toml with serde, and I like suffering.

Would you like for me to PR here if I end up making it happen?