DioxusLabs/dioxus · error · syn::Error

Failed to parse formatted segment: Expected Ident or Express

Error message

Failed to parse formatted segment: Expected Ident or Expression

What it means

ifmt parse error: the text between `{}` in an inline RSX format string is parsed with syn and must be a valid Rust identifier or expression. Anything syn rejects (empty braces, stray tokens, broken syntax) fails with this compile error.

Source

Thrown at packages/rsx/src/ifmt.rs:327

}

#[derive(Debug, PartialEq, Eq, Clone, Hash)]
pub enum FormattedSegmentType {
    Expr(Box<Expr>),
    Ident(Ident),
}

impl FormattedSegmentType {
    fn parse(input: &str) -> Result<Self> {
        if let Ok(ident) = parse_str::<Ident>(input)
            && ident == input
        {
            return Ok(Self::Ident(ident));
        }
        if let Ok(expr) = parse_str(input) {
            Ok(Self::Expr(Box::new(expr)))
        } else {
            Err(Error::new(
                Span::call_site(),
                "Failed to parse formatted segment: Expected Ident or Expression",
            ))
        }
    }
}

impl ToTokens for FormattedSegmentType {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        match self {
            Self::Expr(expr) => expr.to_tokens(tokens),
            Self::Ident(ident) => ident.to_tokens(tokens),
        }
    }
}

impl Parse for IfmtInput {
    fn parse(input: ParseStream) -> Result<Self> {

View on GitHub (pinned to 393d190a80)

Solutions

1. Fix the expression inside the braces so it is valid standalone Rust
2. If the braces are meant to be literal text, escape them as `{{` and `}}`
3. For long or complex expressions, compute the value in a variable first and interpolate only the identifier

Example fix

// before
rsx! { span { "name: {user.name.trim(}" } }

// after
rsx! { span { "name: {user.name.trim()}" } }

When it happens

Trigger: Empty interpolation `"{}"`, mismatched delimiters `"{f(}"`, two identifiers `"{foo bar}"`, or leftover JS template syntax `"${x}"` inside RSX formatted strings.

Common situations: Typos in interpolation expressions; porting JSX/JS template literals that keep `${}`; stray newlines or control characters pasted inside the braces.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• unmatched closing '}' in format string
• expected path param to be wrapped in curly braces
• Only string, int, float, and bool literals are supported
• Catch all segments are not allowed in nests
• 1 issue found.

AI-assisted analysis of DioxusLabs/dioxus@393d190a80 (2026-08-16). Data as JSON: /api/errors/d06f5a71a33f52ae. Report an issue: GitHub.