leptos-rs/leptos · error

positional argument follows keyword argument

Error message

positional argument follows keyword argument

What it means

The `protocol` keyword is also single-use; a second `protocol = ...` in the #[server] attribute triggers this error at the repeated key's span. The parser treats each known option as set-once to prevent ambiguous overrides.

Source

Thrown at server_fn_macro/src/lib.rs:1189

                    } else if key == "impl_from" {
                        if impl_from.is_some() {
                            return Err(syn::Error::new(
                                key.span(),
                                "keyword argument repeated: `impl_from`",
                            ));
                        }
                        impl_from = Some(stream.parse()?);
                    } else if key == "impl_deref" {
                        if impl_deref.is_some() {
                            return Err(syn::Error::new(
                                key.span(),
                                "keyword argument repeated: `impl_deref`",
                            ));
                        }
                        impl_deref = Some(stream.parse()?);
                    } else if key == "protocol" {
                        if protocol.is_some() {
                            return Err(syn::Error::new(
                                key.span(),
                                "keyword argument repeated: `protocol`",
                            ));
                        }
                        protocol = Some(stream.parse()?);
                    } else {
                        return Err(lookahead.error());
                    }
                } else {
                    let value = key_or_value;
                    if use_key_and_value {
                        return Err(syn::Error::new(
                            value.span(),
                            "positional argument follows keyword argument",
                        ));
                    }
                    if arg_pos == 1 {
                        struct_name = Some(value)

View on GitHub (pinned to 32d20f6c9d)

Solutions

1. Keep only one `protocol = ...` argument in the attribute.
2. Remove the obsolete protocol value instead of appending the new one next to it.
3. Search the attribute for all occurrences of `protocol` before editing.

Example fix

// before
#[server(protocol = "grpc", protocol = "grpc-web")]
// after
#[server(protocol = "grpc-web")]

let attr = "#[server(protocol = \"grpc\", protocol = \"grpc-web\")]";
assert!(attr.matches("protocol").count() <= 1, "duplicate `protocol`");

When it happens

Trigger: #[server(protocol = "grpc", protocol = "grpc-web")]; combining a protocol line from one attribute with another attribute's options; templated generation that always appends `protocol`.

Common situations: Migrating between protocol settings (e.g. switching protocols) where the old line was commented as code rather than removed; bulk edits across many server functions.

Related errors

• keyword argument repeated: `impl_deref`
• keyword argument repeated: `protocol`
• expected string literal
• If you use keyword arguments (e.g., `name` = Something), the
• unexpected extra argument

AI-assisted analysis of leptos-rs/leptos@32d20f6c9d (2026-09-01). Data as JSON: /api/errors/b801a9ced64b5620. Report an issue: GitHub.