BoundaryML/baml · error

Class {} does not exist

Error message

Class {} does not exist

What it means

find_existing_class_field receives a ClassWalker wrapped in a Result; if the walker itself is an Err (the class could not be resolved in the codebase), it bails with 'Class {} does not exist'. This is used when resolving fields referenced from jinja helpers/templates against the BAML data model.

Source

Thrown at engine/baml-lib/jsonish/src/helpers/mod.rs:76

        streaming_mode == baml_types::StreamingMode::Streaming,
    )?;

    Ok(OutputFormatContent::target(output.clone())
        .enums(enums)
        .classes(classes)
        .recursive_classes(recursive_classes)
        .structural_recursive_aliases(structural_recursive_aliases)
        .build())
}

fn find_existing_class_field(
    class_name: &str,
    field_name: &str,
    class_walker: &Result<ClassWalker<'_>>,
    env_values: &EvaluationContext<'_>,
) -> Result<(Name, TypeIR, Option<String>, bool)> {
    let Ok(class_walker) = class_walker else {
        anyhow::bail!("Class {} does not exist", class_name);
    };

    let Some(field_walker) = class_walker.find_field(field_name) else {
        anyhow::bail!("Class {} does not have a field: {}", class_name, field_name);
    };

    let name = Name::new_with_alias(field_name.to_string(), field_walker.alias(env_values)?);
    let desc = field_walker.description(env_values)?;
    let r#type = field_walker.r#type();
    let streaming_needed = field_walker.item.attributes.streaming_behavior().needed;
    Ok((name, r#type.clone(), desc, streaming_needed))
}

fn find_enum_value(
    enum_name: &str,
    value_name: &str,
    enum_walker: &Result<EnumWalker<'_>>,
    env_values: &EvaluationContext<'_>,

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Fix the class name in the template/helper call to match a class declared in your .baml files.
2. Search your project for the class definition and confirm it is in a loaded .baml file.
3. Regenerate clients/templates after renames so references stay in sync.
4. Pre-validate referenced class names in CI (e.g. run baml-cli to surface unresolvable references).

Example fix

// before: template references wrong class
{{ ctx.classes["UsrInfo"].name }}
// after
{{ ctx.classes["UserInfo"].name }}

// before invoking template helpers that resolve classes
let class_walker = env.find_class(class_name);
if class_walker.is_err() {
    return Err(anyhow::anyhow!("template references unknown class '{}' — check .baml files", class_name));
}

fn class_resolves(env: &FunctionCfg, name: &str) -> bool { env.find_class(name).is_ok() }

match find_existing_class_field(class_name, field_name, &class_walker, &env) {
    Ok(v) => use_field(v),
    Err(err) => return Err(err.context("template references a class not defined in .baml")),
}

When it happens

Trigger: relevant_data_models calls find_existing_class_field with class_walker = env.find_class/class_walker(name) that returned Err — i.e. the class name in a template helper (e.g. a field-description lookup) has no matching class in the BAML sources.

Common situations: Typos in class names inside jinja templates (e.g. ctx.output_format / description helpers); classes deleted or renamed while templates still reference them; multi-file BAML projects where the class lives in a file not loaded.

Related errors

• Class {name} not found
• Class {} does not have a field: {}
• Enum {} does not exist
• Class '{0}' not found
• Could not unify Class {} with {:?}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/46d5f9ce4a58ee80. Report an issue: GitHub.