BoundaryML/baml · critical

error decoding value

Error message

error decoding value

What it means

convertFieldTypeToGoType panics when the *cffi.CFFIFieldTypeHolder is nil. Field type metadata is required to map a CFFI field to a Go reflect.Type (used by lists, maps, unions, and recursive type conversion); nil means the runtime supplied incomplete type information.

Source

Thrown at engine/language_client_go/baml_go/serde/decode.go:330

	return checkedValue.Elem(), goType
}

func decodeStreamStateType(state cffi.CFFIStreamState) shared.StreamStateType {
	switch state {
	case cffi.CFFIStreamState_PENDING:
		return shared.StreamStatePending
	case cffi.CFFIStreamState_STARTED:
		return shared.StreamStateIncomplete
	case cffi.CFFIStreamState_DONE:
		return shared.StreamStateComplete
	default:
		panic("unexpected stream state")
	}
}

func convertFieldTypeToGoType(fieldType *cffi.CFFIFieldTypeHolder, typeMap TypeMap) reflect.Type {
	if fieldType == nil {
		panic("error decoding value")
	}

	type_ := fieldType.Type

	if _, ok := type_.(*cffi.CFFIFieldTypeHolder_StringType); ok {
		return reflect.TypeOf("")
	}

	if _, ok := type_.(*cffi.CFFIFieldTypeHolder_BoolType); ok {
		return reflect.TypeOf(false)
	}

	if _, ok := type_.(*cffi.CFFIFieldTypeHolder_IntType); ok {
		return reflect.TypeOf(int64(0))
	}

	if _, ok := type_.(*cffi.CFFIFieldTypeHolder_FloatType); ok {
		return reflect.TypeOf(float64(0))

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Regenerate baml_client and rebuild so type metadata matches the runtime
2. Upgrade baml_go bindings to the version matching your BAML CLI
3. Check the .baml schema for exotic types and simplify if on an old version
4. File a bug with the schema and payload that produced nil field metadata

if fieldType == nil { return reflect.TypeOf(nil) }

func hasFieldType(h *cffi.CFFIFieldTypeHolder) bool { return h != nil && h.Type != nil }

defer func() { if r := recover(); r != nil { log.Printf("field type decode failed: %v", r) } }()

When it happens

Trigger: decodeListValue, decodeMapValue, decodeUnionValue, or a recursive convertFieldTypeToGoType call receives a nil field-type holder from the CFFI payload.

Common situations: Runtime/generator version mismatch where field metadata is dropped, corrupted native responses, or BAML schema constructs the installed bindings cannot describe.

Related errors

• decodeUnionValue: valueUnion is nil
• decodeCheckedValue: valueChecked is nil
• unexpected cffi.isCFFIFieldTypeLiteral_Literal: %#v
• field access must be on classes, but expr `{}` got: {other:?
• Invalid type value

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/b0d32613c2863dec. Report an issue: GitHub.