denoland/deno · error · syn::Error

duplicate `options` argument

Error message

duplicate `options` argument

What it means

Same parser as above: `WebIDLArgs::parse` permits at most one `options(...)` group per webidl attribute. It raises this error on the span of the second `options` key; options themselves are a comma-terminated list of WebIDLPairs inside a single group.

Source

Thrown at libs/ops/op2/signature.rs:310

  fn parse(input: ParseStream) -> syn::Result<Self> {
    let mut default: Option<WebIDLDefault> = None;
    let mut options: Vec<WebIDLPair> = Vec::new();

    while !input.is_empty() {
      let key: Ident = input.parse()?;

      if key == "default" {
        if default.is_some() {
          return Err(syn::Error::new(
            key.span(),
            "duplicate `default` argument",
          ));
        }
        input.parse::<Token![=]>()?;
        default = Some(WebIDLDefault(input.parse::<syn::Expr>()?));
      } else if key == "options" {
        if !options.is_empty() {
          return Err(syn::Error::new(
            key.span(),
            "duplicate `options` argument",
          ));
        }
        let content;
        syn::parenthesized!(content in input);
        let parsed_options =
          content.parse_terminated(WebIDLPair::parse, Token![,])?;
        options = parsed_options.into_iter().collect();
      } else {
        return Err(syn::Error::new(
          key.span(),
          "unknown webidl argument, expected `default` or `options`",
        ));
      }

      if !input.is_empty() {
        input.parse::<Token![,]>()?;

View on GitHub (pinned to 9ad36f7a2c)

Solutions

1. Merge all pairs into one `options(...)` group: `options(a = "x", b = "y")`.
2. Delete the stale group left behind by a copy-paste.

Example fix

// before
#[op2(webidl(options(prefix = "-"), options(suffix = "+")))]
mode: String,

// after
#[op2(webidl(options(prefix = "-", suffix = "+")))]
mode: String,

// Compile-time: `cargo check`. When hand-writing, keep all option pairs inside
// a single `options(...)` group: options(a = "x", b = "y").

When it happens

Trigger: `#[op2(webidl(options(a = "x"), options(b = "y")))]` — two `options(...)` groups in one attribute; or repeating `options(...)` after other arguments like `default`.

Common situations: Extending an options list by pasting a second `options(...)` group instead of adding pairs to the existing one.

Related errors

• duplicate `default` argument
• Only ASCII keys are supported
• unknown webidl argument, expected `default` or `options`
• The flags for this attribute were not sorted alphabetically.
• expected attribute arguments in parentheses: `{}(...)`

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/7b948f2820ec52fc. Report an issue: GitHub.