Lazy Loader must define a single input argument to satisfy t

Error message

Lazy Loader must define a single input argument to satisfy the LazyLoader signature

What it means

The lazy_loader! macro was given a function signature whose input count is not exactly one. The LazyLoader<Args, Ret> contract requires a single argument parameter, so signatures with zero or multiple inputs panic at macro expansion.

Source

Thrown at packages/wasm-split/wasm-split-macro/src/lib.rs:133

/// Create a lazy loader for a given function. Meant to be used in statics. Designed for libraries to
/// integrate with.
///
/// ```rust, ignore
/// fn SomeFunction(args: Args) -> Ret {}
///
/// static LOADER: wasm_split::LazyLoader<Args, Ret> = lazy_loader!(SomeFunction);
///
/// LOADER.load().await.call(args)
/// ```
#[proc_macro]
pub fn lazy_loader(input: TokenStream) -> TokenStream {
    // We can only accept idents/paths that will be the source function
    let sig = parse_macro_input!(input as Signature);
    let params = sig.inputs.clone();
    let outputs = sig.output.clone();
    let Some(FnArg::Typed(arg)) = params.first().cloned() else {
        panic!(
            "Lazy Loader must define a single input argument to satisfy the LazyLoader signature"
        )
    };
    let arg_ty = arg.ty.clone();
    let LoaderNames {
        name,
        split_loader_ident,
        impl_import_ident,
        impl_export_ident,
        load_module_ident,
        ..
    } = LoaderNames::new(
        sig.ident.clone(),
        sig.abi
            .as_ref()
            .and_then(|abi| abi.name.as_ref().map(|f| f.value()))
            .expect("abi to be module name")
            .to_string(),

View on GitHub (pinned to 24f6a829df)

Solutions

Define exactly one input argument on the lazy loader so it matches the LazyLoader signature.

Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at packages/wasm-split/wasm-split-macro/src/lib.rs:133 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of DioxusLabs/dioxus@24f6a829df (2026-08-23). Data as JSON: /api/errors/3d553d7496613061. Report an issue: GitHub.