BoundaryML/baml · critical

unexpected cffi.isCFFIFieldTypeLiteral_Literal: %#v

Error message

unexpected cffi.isCFFIFieldTypeLiteral_Literal: %#v

What it means

When a CFFI field type is a literal, the decoder only recognizes Bool, Int, and String literals; any other literal variant hits the default branch and panics with the offending value dumped via %#v. This means the runtime emitted a literal field type the compiled Go bindings do not know.

Source

Thrown at engine/language_client_go/baml_go/serde/decode.go:361

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

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

	if literal, ok := type_.(*cffi.CFFIFieldTypeHolder_LiteralType); ok {
		literalType := literal.LiteralType
		switch literalType.Literal.(type) {
		case *cffi.CFFIFieldTypeLiteral_BoolLiteral:
			return reflect.TypeOf(false)
		case *cffi.CFFIFieldTypeLiteral_IntLiteral:
			return reflect.TypeOf(int64(0))
		case *cffi.CFFIFieldTypeLiteral_StringLiteral:
			return reflect.TypeOf("")
		default:
			panic(fmt.Sprintf("unexpected cffi.isCFFIFieldTypeLiteral_Literal: %#v", literalType.Literal))
		}
	}

	if class, ok := type_.(*cffi.CFFIFieldTypeHolder_ClassType); ok {
		name := class.ClassType.Name.Name
		goType, ok := typeMap.GetType(class.ClassType.Name)
		if !ok {
			// going to be a dynamic class
			return reflect.TypeOf(DynamicClass{
				Name: name,
			})
		}
		return goType
	}

	if enum, ok := type_.(*cffi.CFFIFieldTypeHolder_EnumType); ok {
		name := enum.EnumType.Name
		namespace := cffi.CFFITypeNamespace_TYPES.String()

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Upgrade baml_go bindings and regenerate baml_client so both support the literal type
2. Rebuild the Go binary after upgrading
3. Temporarily replace the unsupported literal in the .baml schema with a plain type
4. Report the %#v payload to BAML maintainers if versions already match

Example fix

// before (schema using unsupported literal on old client)
type Foo string
// after: upgrade bindings, then
// baml-cli generate && go build ./...

func knownLiteral(l cffi.IsCFFIFieldTypeLiteral_Literal) bool {
  switch l.(type) { case *cffi.CFFIFieldTypeLiteral_BoolLiteral, *cffi.CFFIFieldTypeLiteral_IntLiteral, *cffi.CFFIFieldTypeLiteral_StringLiteral: return true }
  return false
}

defer func() { if r := recover(); r != nil { return fmt.Errorf("unsupported literal type: %v", r) } }()

When it happens

Trigger: convertFieldTypeToGoType encounters a CFFIFieldTypeLiteral whose Literal variant is new or unexpected relative to the compiled bindings — typically after a runtime upgrade introduced a new literal kind (e.g. float literals).

Common situations: BAML runtime updated ahead of Go bindings; using a schema feature (new literal type) unsupported by the installed client version.

Related errors

• Invalid type value
• unexpected stream state
• error decoding value
• invalid media type: '%s'
• undefined enum: {enum_name}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/b8b46950273d7acb. Report an issue: GitHub.