BoundaryML/baml · warning · VmBamlError

unsupported: {message}

Error message

unsupported: {message}

What it means

An error value from the BAML standard library, mapping to the `baml.errors.Unsupported` class. It is raised when an operation is recognized but not supported in the current runtime, configuration, or version — a deliberate signal rather than a bug.

Source

Thrown at baml_language/crates/bex_vm_types/src/errors.rs:128

/// An error value from the BAML standard library. Maps 1:1 to a `baml.errors.*` class.
#[derive(Debug, Error, PartialEq, Clone)]
pub enum VmBamlError {
    #[error("invalid argument: {message}")]
    InvalidArgument { message: String },

    #[error("parse error: {message}")]
    ParseError { message: String },

    #[error("I/O error: {message}")]
    Io { message: String },

    #[error("timeout: {message}")]
    Timeout {
        message: String,
        duration_ms: Option<i64>,
    },

    #[error("unsupported: {message}")]
    Unsupported { message: String },

    #[error("access error: {message}")]
    AccessError { message: String },

    #[error("render prompt: {message}")]
    RenderPrompt { message: String },

    #[error("LLM client error: {message}")]
    LlmClient { message: String },

    /// An error value from the host language that has no direct BAML
    /// representation. The `handle` is the load-bearing field — it
    /// references the original host exception object via the
    /// process-global host-value table, so the originating runtime can
    /// recover the exact native exception on round-trip. The
    /// `class_name` / `message` / `language` / `traceback` fields are
    /// purely metadata for debugging, logging, and user-facing

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Check the VM/runtime version and upgrade to one that supports the operation, or enable the required feature flag.
2. Catch `baml.errors.Unsupported` and provide an alternative implementation path for environments lacking the feature.
3. Consult the stdlib docs for platform support notes and guard platform-specific calls.
4. If the operation should be supported, file an issue — it may be a missing feature in the VM.

Example fix

// before
let tz_time = clock.now_in("America/New_York"); // unsupported in this runtime
// after
try {
  let tz_time = clock.now_in("America/New_York");
} catch e: baml.errors.Unsupported {
  let tz_time = clock.now_utc(); // portable fallback
}

// BAML: check feature availability where exposed
if !std.supports("tz_clock") {
  return utc_fallback();
}

try {
  let r = platform_specific_op();
} catch e: baml.errors.Unsupported {
  let r = portable_alternative();
}

When it happens

Trigger: Calling a stdlib function/feature that the current VM build, target platform, or configuration does not implement (e.g. a platform-specific capability, a feature behind a flag, or an operation valid in other runtimes but disabled here).

Common situations: Porting BAML programs between runtimes (native vs WASM/sandbox) where some stdlib features are unavailable; using a newer-language feature on an older VM; relying on optional capabilities (e.g. certain encodings or syscalls) not compiled in.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• unsupported pack target `{target_triple}`
• baml.panics.UserPanic
• baml.errors.InvalidArgument
• parse error: {message}
• I/O error: {message}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/a2f1edb51b641ff2. Report an issue: GitHub.