BoundaryML/baml · error · minijinja::Error

MissingArgument

MissingArgument

Error message

role() called without role. Try role('role') or role(role='role').

What it means

The `role()` function requires a role name from either the positional argument or the `role=` keyword. When both are absent (None positional and no/failed kwarg), it throws MissingArgument with a message showing both accepted call forms.

Source

Thrown at engine/baml-lib/jinja-runtime/src/lib.rs:343

            }),
        );
    }

    let role_fn = minijinja::Value::from_function(
        |role: Option<String>, kwargs: Kwargs| -> Result<String, minijinja::Error> {
            let role = match (role, kwargs.get::<String>("role")) {
                (Some(b), Ok(a)) => {
                    // If both are present, we should error
                    return Err(minijinja::Error::new(
                        ErrorKind::TooManyArguments,
                        format!("role() called with two roles: '{a}' and '{b}'"),
                    ));
                }
                (Some(role), _) => role,
                (_, Ok(role)) => role,
                _ => {
                    // If neither are present, we should error
                    return Err(minijinja::Error::new(
                        ErrorKind::MissingArgument,
                        "role() called without role. Try role('role') or role(role='role').",
                    ));
                }
            };

            let allow_duplicate_role = match kwargs.get::<bool>("__baml_allow_dupe_role__") {
                Ok(allow_duplicate_role) => allow_duplicate_role,
                Err(e) => match e.kind() {
                    ErrorKind::MissingArgument => false,
                    _ => return Err(e),
                },
            };

            let additional_properties = {
                let mut props = kwargs
                    .args()
                    .filter(|&k| k != "role")

View on GitHub (pinned to bd85ce9dee)

Solutions

Pass the role explicitly: `{{ _.role('user') }}` or `{{ _.role(role='assistant') }}`.
If the role is dynamic, ensure the variable is defined and non-null before rendering (e.g. default it in the template: `role(role_name or 'user')`).
Check upstream variable bindings/args so the role value actually reaches the template.

Example fix

// before
{{ _.role() }}Hello

// after
{{ _.role('user') }}Hello

Defensive patterns

Strategy: validation

Validate before calling

// validate role value exists before render
if (!roleName) throw new Error("role() requires a role: role('user') or role(role='user')");

Type guard

function hasRole(args) { return typeof args?.role === "string" && args.role.length > 0; }

Prevention

Default dynamic roles: role(role_var or 'user').
Ensure variables used as role names are defined in the render args map.
Never emit bare role() in templates.

When it happens

Trigger: `{{ role() }}` with no arguments; `{{ role(some_undefined_var) }}` where the variable is undefined/None so the positional is None and the kwarg lookup also fails.

Common situations: Dynamically building role names where the variable is empty or undefined; forgetting the argument when converting plain text to a chat message; template macros rendering role() with an unset parameter.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/d29d24c4cc696579. Report an issue: GitHub.