BoundaryML/baml · error · FormatterError

{0:?}

Error message

{0:?}

What it means

FormatterError::ParseErrors wraps a Vec<ParseError> produced when the baml_fmt formatter fails to parse the input source. The formatter cannot build an AST from a lossy tree, so it collects all parse errors and returns them via this variant; the Display impl debug-prints the error list. It is the top-level formatter error for syntactically invalid BAML input.

Source

Thrown at baml_language/crates/baml_fmt/src/lib.rs:132

    pub line_width: usize,
    /// Indent width. Default: `4`
    pub indent_width: usize,
}
impl Default for FormatOptions {
    fn default() -> Self {
        Self {
            line_width: 100,
            indent_width: CANONICAL_INDENT_WIDTH,
        }
    }
}

/// Canonical indentation used by the CLI, LSP, and default library formatter.
pub const CANONICAL_INDENT_WIDTH: usize = 4;

#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
pub enum FormatterError {
    #[error("{0:?}")]
    ParseErrors(Vec<ParseError>),
    #[error("{0}")]
    StrongAstError(#[from] ast::StrongAstError),
}

#[cfg(test)]
mod format_options_tests {
    use super::*;

    #[test]
    fn default_options_use_the_canonical_four_space_indent() {
        let options = FormatOptions::default();
        assert_eq!(CANONICAL_INDENT_WIDTH, 4);
        assert_eq!(options.indent_width, CANONICAL_INDENT_WIDTH);
        let formatted = format("function value() -> int {\n  result\n}\n", &options)
            .expect("default formatter options should format a function body");
        assert_eq!(formatted, "function value() -> int {\n    result\n}\n");
    }

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Fix the BAML syntax errors listed in the wrapped ParseErrors (each includes its range) before formatting
2. Run the parser/`baml` CLI diagnostics on the file to enumerate all errors
3. Upgrade baml_fmt/parser if the file uses syntax newer than the installed toolchain
4. Exclude generated or known-bad files from format-on-save until they are valid

Example fix

// before (unclosed string)
prompt "
Hello
// after
prompt "
Hello
"

// before formatting, run the parser and bail on any errors
let (tree, errors) = parse_baml(source);
if !errors.is_empty() {
    return Err(FormatterError::ParseErrors(errors)); // handle before formatting
}

match format_source(source) {
    Ok(formatted) => save(formatted),
    Err(FormatterError::ParseErrors(errs)) => {
        for e in errs { report_parse_error(e); }
        // skip writing formatted output
    }
    Err(e) => report_other(e),
}

When it happens

Trigger: Calling the formatter (CLI format, LSP formatting, or library format API) on BAML source containing syntax errors — the parse step yields one or more ParseErrors which are returned wrapped in this variant.

Common situations: Formatting a file with typos, unclosed braces/strings, or unsupported/newer syntax; running `baml fmt` on an in-progress edit; LSP format-on-save over a broken buffer; formatting files from a newer BAML version with an older formatter.

Understand the failure class

Background: JSON parse error: "Unexpected token" / "not valid JSON" / "failed to parse" — what JSON parsers are really complaining about — this error's family across 45 libraries.

Related errors

• Expected token/node of kind {expected:?}, but found {found:?
• Expected token/node {expected_desc}, but found {found:?} at
• Expected token/node of kind {expected:?}, but was unable to
• Expected token/node {desc}, but was unable to find it in {pa
• Unexpected additional element at {at:?} in {parent:?}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/55670d0591f26a8b. Report an issue: GitHub.