altsrc and StringSlice

[jvilhuber]

Version: github.com/urfave/cli/v2 v2.24.4

I have this habit of using cli arguments that immediately populate a struct:

type ServerArguments struct {
	Addresses    cli.StringSlice        `yaml:"address" json:"address"`
	ClientConfig grpc.ClientConfigs     `yaml:"client-config" json:"client-config"`
}

func (sa *ServerArguments) GetCliFlags(prefix string) []cli.Flag {
	cliFlags := []cli.Flag{
		altsrc.NewStringSliceFlag(&cli.StringSliceFlag{
			Name:        prefix + ".address",
			Usage:       "List of Grpc addresses. Can be given multiple times",
			Value:       &cli.StringSlice{}, // could also be 'nil'. same problem
			Destination: &sa.Addresses,
		}),
	}
	cliFlags = append(cliFlags, sa.ClientConfig.GetCliFlags("client-config")...)
	return cliFlags
}

This is very convenient to simply adding these grpc options to other structs. You can see this in the cliFlags = append(cliFlags... line, where I add another sub-struct I reuse in multiple places.

I usually test my configs by having a Makefile target that does something like:

myProgram --dump-config yaml > config.yaml-example
myProgram --config config.yaml-example --dump-config yaml

(i.e. read the default, empty, config I generated in step 1, and parsing it). This errors, because the generated yaml config is

address: {}

Error:

Expected '[]interface{}' but actual is ''

Code to generate the yaml config is something like

		encoder := yaml.NewEncoder(c.App.Writer)
		err := encoder.Encode(cliArguments)

where cliArguments is a set of nested cli.Flags. This all works great for all types I've used so far, EXCEPT the StringSlice.

Is there something I'm not seeing that I should change? Or do I need to provide some yaml-encoder for StringSlice (as mentioned in some google search results I've found)? If so, wouldn't it be better to pull those into the cli.urfave package?

Thanks!