BoundaryML/baml · error

Invalid type value

Error message

Invalid type value

What it means

An expect("Invalid type value") panic in parse_base_type. The code first string-matches the identifier against known primitive names (string, int, float, bool, image, audio, pdf, video) and then calls TypeValue::from_str(...).expect(...), assuming from_str cannot fail for those names. If the match arms and TypeValue::from_str ever disagree (new alias added to one but not the other), the expect panics.

Source

Thrown at engine/baml-lib/ast/src/parser/parse_types.rs:173

                ));
                // Return a Symbol type to allow type validation to continue
                // This will trigger the "type not found" error in the validation pipeline
                Some(FieldType::Symbol(
                    FieldArity::Required,
                    Identifier::Local(
                        current.as_str().to_string(),
                        diagnostics.span(current.as_span()),
                    ),
                    None,
                ))
            }
            Rule::identifier => {
                let identifier = parse_identifier(current.clone(), diagnostics);
                let field_type = match current.as_str() {
                    "string" | "int" | "float" | "bool" | "image" | "audio" | "pdf" | "video" => {
                        FieldType::Primitive(
                            FieldArity::Required,
                            TypeValue::from_str(identifier.name()).expect("Invalid type value"),
                            diagnostics.span(current.as_span()),
                            None,
                        )
                    }
                    "null" => FieldType::Primitive(
                        FieldArity::Optional,
                        TypeValue::Null,
                        diagnostics.span(current.as_span()),
                        None,
                    ),
                    "true" => FieldType::Literal(
                        FieldArity::Required,
                        LiteralValue::Bool(true),
                        diagnostics.span(current.as_span()),
                        None,
                    ),
                    "false" => FieldType::Literal(
                        FieldArity::Required,

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Use a standard BAML primitive type name in your .bml file (string, int, float, bool, image, audio, pdf, video) at the reported span
2. Check for case sensitivity: `String` vs `string` — use the lowercase canonical form
3. Report the input upstream if a documented type name panics — the match list and TypeValue::from_str are out of sync
4. When adding primitives, update both the match arms in parse_base_type and TypeValue::from_str together

Example fix

// before
field String
// after
field string

const PRIMITIVES: &[&str] = &["string","int","float","bool","image","audio","pdf","video"];
fn is_known_primitive(t: &str) -> bool {
    PRIMITIVES.contains(&t.trim())
}
// call before referencing the type in .bml or invoking the parser

fn as_type_value(t: &str) -> Option<&str> {
    match t.trim() {
        "string" | "int" | "float" | "bool" | "image" | "audio" | "pdf" | "video" => Some(t.trim()),
        _ => None,
    }
}

std::panic::catch_unwind(|| parse_base_type(pair, &mut diagnostics))
    .map_err(|_| diagnostics.push("primitive name not recognized by TypeValue::from_str"));

When it happens

Trigger: parse_base_type parsing a Rule::identifier whose string is in the primitive match list but not recognized by TypeValue::from_str — i.e. drift between the literal match list and the TypeValue enum's FromStr impl. Not reachable from valid .bml input with matched lists.

Common situations: Hit during BAML development when adding a new primitive type to the match arms without updating TypeValue::from_str (or vice versa), or when case-sensitivity changes make the same literal parse differently.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Name should always be defined for attribute.
• Encountered impossible doc comment during parsing: {:?}, {:?
• c_for_init_stmt cannot accept empty input
• c_for_after_stmt cannot accept empty input
• block aware tail expression is not empty

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/a3df2d44036fe3c5. Report an issue: GitHub.