BoundaryML/baml · error · BridgeError

CallFunctionArgs.call_target must be set

Error message

CallFunctionArgs.call_target must be set

What it means

BridgeError::MissingCallTarget from the bridge_cffi crate. It is raised when a call_function operation is invoked with CallFunctionArgs whose call_target field was never set. The bridge needs to know which BAML function to invoke; a null/absent call_target is rejected before any lookup happens.

Source

Thrown at baml_language/crates/bridge_cffi/src/error.rs:22

/// Errors that can occur during bridge operations.
#[derive(Debug, Error)]
pub enum BridgeError {
    #[error(transparent)]
    Ctypes(#[from] bridge_ctypes::CtypesError),
    #[error("Engine not initialized. Call create_baml_runtime first.")]
    NotInitialized,

    #[error("Project not initialized")]
    ProjectNotInitialized,

    #[error("Engine lock poisoned")]
    LockPoisoned,

    #[error("{0}")]
    Runtime(#[from] bex_project::RuntimeError),

    #[error("CallFunctionArgs.call_target must be set")]
    MissingCallTarget,

    #[error("type arguments are not supported when invoking a BAML function handle")]
    FunctionHandleTypeArgs,

    #[error("Function not found: {name}")]
    FunctionNotFound { name: String },

    #[error("Missing argument '{parameter}' for function '{function}'")]
    MissingArgument { function: String, parameter: String },

    #[error("Not implemented: {0}")]
    NotImplemented(String),

    #[error("call_id {0} is already in use by an active call")]
    DuplicateCallId(u64),

    #[error("call_id must be a nonzero uint64")]

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Set CallFunctionArgs.call_target to the name of the BAML function you want to invoke before calling.
2. If using ctypes, explicitly assign the field rather than relying on zero-initialized memory.
3. Regenerate or update FFI bindings so the call_target field exists and is populated.
4. Add a client-side assert that call_target is a non-empty string before invoking.

Example fix

// before
let args = CallFunctionArgs { call_id: 1, ..Default::default() };
// after
let args = CallFunctionArgs { call_id: 1, call_target: Some("ExtractResume".into()), ..Default::default() };

if not args.call_target:
    raise ValueError("call_target must be set before invoking")

def has_call_target(args) -> bool:
    return bool(getattr(args, 'call_target', None))

try:
    bridge.call_function(args)
except BridgeError as e:
    if 'call_target must be set' in str(e):
        fix_and_retry_with_target(args)

When it happens

Trigger: Calling the bridge's function-invocation entry point with CallFunctionArgs constructed without assigning call_target (e.g. left at its default/None), typically via the CFFI/ctypes layer.

Common situations: Hand-building the args struct in FFI bindings and forgetting a field; zero-initialized structs in C/ctypes where an empty string or null target silently passes validation; code generated from outdated bindings missing the call_target field.

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

• Missing argument '{parameter}' for function '{function}'
• call_id must be a nonzero uint64
• {0}
• Invalid bigint hex string ({len} bytes)
• Invalid decimal bigint literal ({len} bytes)

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/6d126645c6206e66. Report an issue: GitHub.