if _, file, line, ok := runtime.Caller(1); ok {
			msg = fmt.Sprintf("%s:%d: %s", file, line, msg)
		}
		panic(msg)
	}
}

// An errorDesc describes part of a type-checking error.
type errorDesc struct {
	pos syntax.Pos
	msg string
}

// An error_ represents a type-checking error.
// A new error_ is created with Checker.newError.

		b.WriteString(e.Err.Error())
	} else {
		for _, elem := range stack[:len(stack)-1] {
			fmt.Fprintf(b, "%s %s\n\t", elem.m, elem.nextReason)
		}
		// Ensure that the final module path and version are included as part of the
		// error message.
		m := stack[len(stack)-1].m
		if mErr, ok := e.Err.(*module.ModuleError); ok {
			actual := module.Version{Path: mErr.Path, Version: mErr.Version}