yewstack/yew · error · syn::Error

expected enum, found struct

Error message

expected enum, found struct

What it means

The #[derive(Routable)] macro (packages/yew-router-macro/src/routable_derive.rs:44) only accepts enums: a route model is a closed set of variants, each mapped to a URL pattern by an #[at("...")] attribute. Applying the derive to a struct is rejected at the struct token with 'expected enum, found struct'.

Source

Thrown at packages/yew-router-macro/src/routable_derive.rs:44

    }
    params
}

pub struct Routable {
    ident: Ident,
    ats: Vec<LitStr>,
    variants: Punctuated<Variant, syn::token::Comma>,
    not_found_route: Option<Ident>,
}

impl Parse for Routable {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let DeriveInput { ident, data, .. } = input.parse()?;

        let data = match data {
            Data::Enum(data) => data,
            Data::Struct(s) => {
                return Err(syn::Error::new(
                    s.struct_token.span(),
                    "expected enum, found struct",
                ));
            }
            Data::Union(u) => {
                return Err(syn::Error::new(
                    u.union_token.span(),
                    "expected enum, found union",
                ));
            }
        };

        let (not_found_route, ats) = parse_variants_attributes(&data.variants)?;

        Ok(Self {
            ident,
            variants: data.variants,
            ats,

View on GitHub (pinned to 0e4a05472f)

Solutions

1. Convert the item into an enum where each variant is one route, with #[at("/path")] on every variant
2. Use named fields on variants that capture route parameters (e.g. Post { id: u32 }) and unit variants for static routes
3. If the struct must stay, remove the Routable derive and map the struct from an enum route model instead

Example fix

// before
#[derive(Routable, Clone)]
struct Routes {
    home: (),
}

// after
#[derive(Routable, Clone)]
enum Routes {
    #[at("/")]
    Home,
}

// before deriving, confirm the item is an enum with one #[at] per variant
// #[derive(Routable, Clone)]
// enum Routes { #[at("/")] Home, #[at("/about")] { /* ... */ } About }

// compile-time shape check: fails to compile if Routes is not an enum
const _: fn(Routes) -> Routes = |r| match r { _ => r };

When it happens

Trigger: Annotating a struct with #[derive(Routable)], e.g. #[derive(Routable, Clone)] struct Routes { home: () }. The derive input parser rejects Data::Struct before any route processing.

Common situations: Coming from routers where routes are a config struct or builder (actix, axum-style); holding route metadata in a struct and adding the derive as an afterthought; copy-pasting a derive list onto the wrong item.

Related errors

• expected enum, found union
• only named fields are supported
• at attribute must be present on every variant
• this hook takes 2 arguments but 1 argument was supplied
• this hook takes 2 arguments but 1 argument was supplied

AI-assisted analysis of yewstack/yew@0e4a05472f (2026-08-22). Data as JSON: /api/errors/99c647cb61d4c889. Report an issue: GitHub.