BoundaryML/baml · error · EngineError

Schema inconsistency: {message}

Error message

Schema inconsistency: {message}

What it means

An internal consistency check on schema/type metadata failed: the engine found schema state that violates its own invariants (e.g. a type referenced that the schema does not define consistently). Like VmInternalError this usually indicates a bug rather than user error.

Source

Thrown at baml_language/crates/bex_engine/src/lib.rs:848

    UnhandledThrow {
        value: Box<BexExternalValue>,
        trace: Vec<bex_vm::StackFrame>,
    },

    /// Clean process-termination request from `baml.sys.exit(code)`.
    /// The caller is expected to honor this as the process exit code.
    /// BAML `int` is `i64`, so the signal carries the full value; the
    /// caller clamps into its shell's range (typically 0..=255 on Unix).
    #[error("baml.sys.exit({code})")]
    Exit { code: i64 },

    #[error("Cannot convert object of type {type_name}")]
    CannotConvert { type_name: String },

    #[error("Type mismatch: {message}")]
    TypeMismatch { message: String },

    #[error("Schema inconsistency: {message}")]
    SchemaInconsistency { message: String },

    #[cfg(feature = "heap_debug")]
    #[error("Snapshot not possible for type: {type_name}")]
    CannotSnapshot { type_name: String },

    #[error("A function call with ID {call_id} is already in progress")]
    DuplicateCallId { call_id: CallId },

    #[error("Package initialization failed: {0}")]
    InitFailed(String),

    #[error("{0}")]
    Other(String),
}

fn format_vm_internal_error(
    err: &bex_vm::errors::VmInternalError,

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Regenerate/recompile the BAML package schema from source
2. Align compiler and engine crate versions
3. Remove hand-edits from generated schema artifacts
4. Report upstream with the message if it persists on a clean rebuild

Example fix

// before: stale artifacts
.baml_cache/ (old schema)
// after: clean rebuild
rm -rf .baml_cache && baml build

// before loading: verify schema artifacts exist and were just generated
assert!(pkg.schema_path().exists());
assert_eq!(pkg.compiler_version(), ENGINE_VERSION);

match result {
    Err(EngineError::SchemaInconsistency { message }) => {
        eprintln!("schema invalid, rebuild: {message}");
        rebuild_package()?;
    }
    Ok(v) => use(v),
    Err(e) => handle(e),
}

When it happens

Trigger: Loading or linking a BAML package whose type/schema metadata is inconsistent — duplicate definitions, missing referenced types, or corrupted IR reaching the engine.

Common situations: Stale or partially regenerated compiled schemas; version skew between the compiler that produced the schema and the engine loading it; hand-edited generated files.

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

• Non-regular recursive generic class '{class}' expands from '
• Output definitions '{first}' and '{second}' both render as '
• Type alias definitions for '{rendered_name}' have non-equiva
• pack produced no output at {}
• Type alias not found: {name}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/55c55f99e2bd3210. Report an issue: GitHub.