Fix StringMap and StringsMap

[hoshsadiq]

When calling StringMap, or StringsMap, and the ko.Get() returns
the value as expected, e.g. map[string]string for StringMap, the
type assertion for map[string]interface{} does not match. This
causes it to return an empty map even when there are actual values.

This commit addresses this by simply returning a copy if the type
assertion matches what we're supposed to return.

[hoshsadiq]

@knadh I'm not sure where the place is to add a test case for it, as all the current test cases always retrieve map[string]interface{}. I figured adding a new test case just for this didn't make sense and thought it's worth checking first. Let me know where a good place is to add tests and I'd be happy to add them.

[knadh]

Thanks for the PR @hoshsadiq.

When calling StringMap, or StringsMap, and the ko.Get() returns the value as expected, e.g. map[string]string for StringMap, the type assertion for map[string]interface{} does not match. This causes it to return an empty map even when there are actual values.

I'm a little confused by this. Could you share some example code that demonstrates this?

[hoshsadiq]

Example:

package main

import (
	"fmt"
	"log"

	"github.com/knadh/koanf"
	"github.com/knadh/koanf/providers/structs"
)

type parentStruct struct {
	MapStrStr   map[string]string      `koanf:"mpss"`
	MapStrIface map[string]interface{} `koanf:"mpsi"`
}

func main() {
	in := parentStruct{
		MapStrStr: map[string]string{
			"hello": "test",
		},
		MapStrIface: map[string]interface{}{
			"hello": "test",
		},
	}

	var k = koanf.New(".")
	if err := k.Load(structs.Provider(in, "koanf"), nil); err != nil {
		log.Fatalf("error loading config: %v", err)
	}

	fmt.Println("mpss = ", k.StringMap("mpss"))
	fmt.Println("mpsi = ", k.StringMap("mpsi"))
}

Output:

mpss =  map[]
mpsi =  map[hello:test]

With this fix output is:

mpss =  map[hello:test]
mpsi =  map[hello:test]

[knadh]

Looks good. @rhnvrm could you please review as well?

[rhnvrm]

LGTM

[hoshsadiq]

Thanks both!