BoundaryML/baml · error

internal error: cannot convert value

Error message

internal error: cannot convert value {value} to VM value: class '{name}' not found in VM objects

What it means

A continuation of the class lookup: the class name WAS found in resolved_class_names, but the object stored at that index in the VM is not a Class object. The runtime treats this as an internal invariant violation, since the index mapping and VM object table should be consistent.

Solutions

1. Report the bug to the BAML repository with the full error and reproduction steps
2. Ensure baml-runtime, baml-compiler, and generated client versions are all from the same release
3. Rebuild/reinstall the BAML runtime to rule out stale artifacts

// treat as internal bug: log full error and report upstream
Err(e) if e.to_string().starts_with("internal error:") => { log::error!("baml bug: {e}"); panic!() }

When it happens

Trigger: VM object table corrupted or mismatched with resolved class indices — this should be unreachable in normal use and indicates a bug in the BAML runtime (or custom/patched VM usage).

Common situations: Hitting it in practice usually means running a mismatched mix of runtime/compiler versions, or a genuine BAML bug; report it with a reproduction.

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

• internal error
• internal error: cannot convert value
• ======================================== BAML Internal…
• cannot convert value
• cannot convert value

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/09bdb435954f68c8. Report an issue: GitHub.

Appendix: source

Thrown at engine/baml-runtime/src/async_vm_runtime.rs:1284

                    try_vm_value_from_baml_value(
                        vm,
                        resolved_class_names,
                        resolved_enums_names,
                        v,
                    )?,
                );
            }

            Ok(vm.alloc_map(vm_map))
        }

        BamlValue::Class(name, fields) => {
            let Some(class_index) = resolved_class_names.get(name) else {
                anyhow::bail!("cannot convert value {value} to VM value: class '{name}' not found");
            };

            let baml_vm::Object::Class(class) = &vm.objects[*class_index] else {
                anyhow::bail!(
                    "internal error: cannot convert value {value} to VM value: class '{name}' not found in VM objects"
                );
            };

            let mut ordered_field_values = Vec::new();
            for field_name in &class.field_names {
                let Some(value) = fields.get(field_name) else {
                    anyhow::bail!(
                        "cannot convert value {value} to VM value: class '{name}' has no field '{field_name}'"
                    );
                };

                ordered_field_values.push(value);
            }

            let mut vm_fields_layout = Vec::new();
            for v in ordered_field_values {
                vm_fields_layout.push(try_vm_value_from_baml_value(

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