DioxusLabs/dioxus · error · syn::Error

keyword argument repeated: `input`

Error message

keyword argument repeated: `input`

What it means

The `input = ...` key (input codec for a `#[server]` function) may be specified at most once. A second `input` occurrence — or one following `encoding` — is rejected (packages/fullstack-macro/src/lib.rs:1595-1600).

Source

Thrown at packages/fullstack-macro/src/lib.rs:1596

                        }
                        encoding = Some(stream.parse()?);
                    } else if key == "endpoint" {
                        if fn_path.is_some() {
                            return Err(syn::Error::new(
                                key.span(),
                                "keyword argument repeated: `endpoint`",
                            ));
                        }
                        fn_path = Some(stream.parse()?);
                    } else if key == "input" {
                        if encoding.is_some() {
                            return Err(syn::Error::new(
                                key.span(),
                                "`encoding` and `input` should not both be \
                                 specified",
                            ));
                        } else if input.is_some() {
                            return Err(syn::Error::new(
                                key.span(),
                                "keyword argument repeated: `input`",
                            ));
                        }
                        input = Some(stream.parse()?);
                    } else if key == "input_derive" {
                        if input_derive.is_some() {
                            return Err(syn::Error::new(
                                key.span(),
                                "keyword argument repeated: `input_derive`",
                            ));
                        }
                        input_derive = Some(stream.parse()?);
                    } else if key == "output" {
                        if encoding.is_some() {
                            return Err(syn::Error::new(
                                key.span(),
                                "`encoding` and `output` should not both be \

View on GitHub (pinned to 393d190a80)

Solutions

1. Keep a single `input = ...` entry.
2. If layering is needed (compression, custom formats), implement one custom codec type implementing the codec traits and reference it once.
3. Lint attributes for duplicate keys after automated edits.

Example fix

// before
#[server(input = Json, input = Multipart)]
async fn upload(file: Vec<u8>) { ... }

// after
#[server(input = Multipart)]
async fn upload(file: Vec<u8>) { ... }

# Reuse the duplicate-key checker from index 93; input is in its key list.

When it happens

Trigger: `#[server(input = Json, input = Multipart)]`; copy-paste duplication; attempting to layer codecs (e.g. compressed JSON) by listing `input` twice.

Common situations: Refactors that append rather than replace attribute args; merge conflicts; scaffolding templates that already include an `input` key.

Related errors

• keyword argument repeated: `encoding`
• `encoding` and `input` should not both be specified
• keyword argument repeated: `name`
• keyword argument repeated: `prefix`
• keyword argument repeated: `endpoint`

AI-assisted analysis of DioxusLabs/dioxus@393d190a80 (2026-08-16). Data as JSON: /api/errors/540d250427a3876f. Report an issue: GitHub.