Support slices of complex types

[tarik-hamani-by]

Slices of complex types are not taken into account.

E.g.

type Config struct {
	Foo []Test `envPrefix:"FOO"`
}
type Test struct {
	Bar string `env:"BAR"`
}

currently results in the following generated file:

# Environment Variables

## Config

 - `FOO_BAR` - 

although the environment variables would be:
FOO_0_BAR, FOO_1_BAR, etc.

[g4s8]

Could you provide any working example with this case? As I see https://github.com/caarlos0/env doesn't support any custom struct for slice types. e.g this example doesn't work for me:

package main

import (
	"log"

	"github.com/caarlos0/env"
)

type Config struct {
	Foo []Test `envPrefix:"FOO"`
}
type Test struct {
	Bar string `env:"BAR"`
}

func main() {
	var cfg Config
	if err := env.Parse(&cfg); err != nil {
		log.Fatal(err)
	}
	log.Printf("%+v", cfg)
}

and env FOO_BAR=1 go run main.go prints empty config

[tarik-hamani-by]

In your example, since you're not specifying the version of https://github.com/caarlos0/env in your imports, you're importing v1, but the current version is v11.

Here's a working example:

package main

import (
	"log"
	"os"

	"github.com/caarlos0/env/v11"
)

type Config struct {
	Foo []Test `envPrefix:"FOO"`
}
type Test struct {
	Bar string `env:"BAR"`
}

func main() {
	os.Setenv("FOO_0_BAR", "foobar")

	var cfg Config
	if err := env.Parse(&cfg); err != nil {
		log.Fatal(err)
	}
	log.Printf("%+v\n", cfg)
}

Here's an example in the repo:
https://github.com/caarlos0/env/blob/52e7186e71f67e4259b6f1f8d6a889368f4e3378/example_test.go#L299

[tarik-hamani-by]

How about introducing a placeholder for the index like this?

# Environment Variables

## Config

 - `FOO_#_BAR` -