DioxusLabs/dioxus · error · syn::Error

Expected middleware attribute to be a list, e.g. #[middlewar

Error message

Expected middleware attribute to be a list, e.g. #[middleware(MyLayer::new())]

What it means

Error "Expected middleware attribute to be a list, e.g. #[middleware(MyLayer::new())]" thrown in DioxusLabs/dioxus.

Source

Thrown at packages/fullstack-macro/src/lib.rs:216

fn route_impl_with_route(
    route: Route,
    item: TokenStream,
    method_from_macro: Option<Method>,
) -> syn::Result<TokenStream2> {
    // Parse the route and function
    let mut function = syn::parse::<ItemFn>(item)?;

    // Collect the middleware initializers
    let middleware_layers = function
        .attrs
        .iter()
        .filter(|attr| attr.path().is_ident("middleware"))
        .map(|f| match &f.meta {
            Meta::List(meta_list) => Ok({
                let tokens = &meta_list.tokens;
                quote! { .layer(#tokens) }
            }),
            _ => Err(Error::new(
                f.span(),
                "Expected middleware attribute to be a list, e.g. #[middleware(MyLayer::new())]",
            )),
        })
        .collect::<Result<Vec<_>>>()?;

    // don't re-emit the middleware attribute on the inner
    function
        .attrs
        .retain(|attr| !attr.path().is_ident("middleware"));

    // Attach `#[allow(unused_mut)]` to all original inputs to avoid warnings
    let outer_inputs = function
        .sig
        .inputs
        .iter()
        .enumerate()
        .map(|(i, arg)| match arg {

View on GitHub (pinned to 393d190a80)

When it happens

Trigger: Thrown at packages/fullstack-macro/src/lib.rs:216 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of DioxusLabs/dioxus@393d190a80 (2026-08-16). Data as JSON: /api/errors/897be4a28f470bdd. Report an issue: GitHub.