docker/cli · error

invalid type %T for string list

Error message

invalid type %T for string list

What it means

Error "invalid type %T for string list" thrown in docker/cli.

Source

Thrown at cli/compose/loader/loader.go:800

}

var transformStringOrNumberList TransformerFunc = func(value any) (any, error) {
	list := value.([]any)
	result := make([]string, len(list))
	for i, item := range list {
		result[i] = fmt.Sprint(item)
	}
	return result, nil
}

var transformStringList TransformerFunc = func(data any) (any, error) {
	switch value := data.(type) {
	case string:
		return []string{value}, nil
	case []any:
		return value, nil
	default:
		return data, fmt.Errorf("invalid type %T for string list", value)
	}
}

var transformHostsList TransformerFunc = func(data any) (any, error) {
	hl := transformListOrMapping(data, ":", false, []string{"=", ":"})

	// Remove brackets from IP addresses if present (for example "[::1]" -> "::1").
	result := make([]string, 0, len(hl))
	for _, hip := range hl {
		host, ip, _ := strings.Cut(hip, ":")
		if len(ip) > 2 && ip[0] == '[' && ip[len(ip)-1] == ']' {
			ip = ip[1 : len(ip)-1]
		}
		result = append(result, fmt.Sprintf("%s:%s", host, ip))
	}
	return result, nil
}

View on GitHub (pinned to e9452d6e78)

When it happens

Trigger: Thrown at cli/compose/loader/loader.go:800 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/461b2f87ca7dfbba.json. Report an issue: GitHub.