What causes "unexpected static parameter" in rwf2/Rocket?

Wrap the parameter name in angle brackets: data = " "

rwf2/Rocket · error · rocket_codegen::param::Error

Static

Static

Error message

unexpected static parameter

What it means

This is a compile-time codegen error from Rocket's route/attribute parameter parser. Dynamic::parse expects a dynamic parameter of the form <name> (optionally trailing, <name..>); when Parameter::parse classifies the segment as Parameter::Static (no surrounding angle brackets), Dynamic::parse rejects it with ErrorKind::Static ('unexpected static parameter'). It appears in attribute positions that require a dynamic parameter binding, such as data = "<param>" on a route or other FromMeta contexts that parse a Dynamic.

Source

Thrown at core/codegen/src/attribute/param/parse.rs:38

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum ErrorKind {
    Empty,
    BadIdent,
    Ignored,
    EarlyTrailing,
    NoTrailing,
    Static,
}

impl Dynamic {
    pub fn parse<P: Part>(
        segment: &str,
        span: Span,
    ) -> Result<Self, Error<'_>>  {
        match Parameter::parse::<P>(segment, span)? {
            Parameter::Dynamic(d) | Parameter::Ignored(d) => Ok(d),
            Parameter::Guard(g) => Ok(g.source),
            Parameter::Static(_) => Err(Error::new(segment, span, ErrorKind::Static)),
        }
    }
}

impl Parameter {
    pub fn parse<P: Part>(
        segment: &str,
        source_span: Span,
    ) -> Result<Self, Error<'_>>  {
        let mut trailing = false;

        // Check if this is a dynamic param. If so, check its well-formedness.
        let lint = Lint::SegmentChars;
        if segment.starts_with('<') && segment.ends_with('>') {
            let mut name = &segment[1..(segment.len() - 1)];
            if name.ends_with("..") {
                trailing = true;
                name = &name[..(name.len() - 2)];

View on GitHub (pinned to 3a54d079ae)

Solutions

Wrap the parameter name in angle brackets: data = "<payload>"
Check the exact attribute position the error span points at — only route paths allow static segments; parameter bindings like data = require <name>
Re-run cargo check to confirm the span now parses

Example fix

// before
#[post("/upload", data = "payload")]
fn upload(payload: TempFile<'_>) { }

// after
#[post("/upload", data = "<payload>")]
fn upload(payload: TempFile<'_>) { }

Defensive patterns

Strategy: validation

Prevention

Treat data = "<name>" as the only valid form — angle brackets required
Match the name inside <...> exactly to the handler argument name
Run cargo check early after editing route macros to catch codegen errors before runtime

When it happens

Trigger: Writing a static string where a dynamic parameter is required, e.g. #[post("/upload", data = "payload")] instead of data = "<payload>", or any attribute value parsed via the FromMeta impl for Dynamic that lacks <...> delimiters.

Common situations: Forgetting the angle brackets on the data parameter of a route macro; copying a query string field name style (id=5) into a dynamic-parameter slot; muscle memory from other frameworks where the parameter name is bare.

Related errors

AI-assisted analysis of rwf2/Rocket@3a54d079ae (2026-08-16). Data as JSON: /api/errors/c272b77dcec6156f. Report an issue: GitHub.