docker/cli · error

expected func, got %v

Error message

expected func, got %v

What it means

Error "expected func, got %v" thrown in docker/cli.

Source

Thrown at cli/command/formatter/reflect.go:57

	for i := 0; i < val.NumMethod(); i++ {
		k, v, err := marshalForMethod(typ.Method(i), val.Method(i))
		if err != nil {
			return nil, err
		}
		if k != "" {
			m[k] = v
		}
	}
	return m, nil
}

var unmarshallableNames = map[string]struct{}{"FullHeader": {}}

// marshalForMethod returns the map key and the map value for marshalling the method.
// It returns ("", nil, nil) for valid but non-marshallable parameter. (e.g. "unexportedFunc()")
func marshalForMethod(typ reflect.Method, val reflect.Value) (string, any, error) {
	if val.Kind() != reflect.Func {
		return "", nil, fmt.Errorf("expected func, got %v", val.Kind())
	}
	name, numIn, numOut := typ.Name, val.Type().NumIn(), val.Type().NumOut()
	_, blackListed := unmarshallableNames[name]
	// FIXME: In text/template, (numOut == 2) is marshallable,
	//        if the type of the second param is error.
	marshallable := unicode.IsUpper(rune(name[0])) && !blackListed &&
		numIn == 0 && numOut == 1
	if !marshallable {
		return "", nil, nil
	}
	result := val.Call(make([]reflect.Value, numIn))
	intf := result[0].Interface()
	return name, intf, nil
}

View on GitHub (pinned to e9452d6e78)

When it happens

Trigger: Thrown at cli/command/formatter/reflect.go:57 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of docker/cli@e9452d6e78 (2026-08-01). Data as JSON: /data/errors/5fe33684ea3f0bd1.json. Report an issue: GitHub.