Array items are overwritten and not merged

[aeneasr]

Describe the bug

When loading two providers that have a key which contains an array, the first array item is replaced completely and the contents are not merged.

To Reproduce

package configx

import (
	stdjson "encoding/json"
	"github.com/knadh/koanf"
	"github.com/knadh/koanf/parsers/json"
	"github.com/knadh/koanf/providers/rawbytes"
	"testing"
)

func TestKoanfMergeArray(t *testing.T) {
	k := koanf.NewWithConf(koanf.Conf{Delim: Delimiter, StrictMerge: true})
	if err := k.Load(rawbytes.Provider([]byte(`{"foo":[{"id":"bar"}]}`)), json.Parser()); err != nil {
		t.Fatal(err)
	}

	if err := k.Load(rawbytes.Provider([]byte(`{"foo":[{"key":"baz"}]}`)), json.Parser()); err != nil {
		t.Fatal(err)
	}

	expected := `{"foo":[{"id":"bar","key":"baz"}]}`
	out, _ := stdjson.Marshal(k.All())
	if string(out) != expected {
		t.Fatalf("Expected %s but got: %s", expected, out)
	}
}

Returns:

Expected {"foo":[{"id":"bar","key":"baz"}]} but got: {"foo":[{"key":"baz"}]}

Expected behavior

Expected to receive:

 {"foo":[{"id":"bar","key":"baz"}]}

Please provide the following information):

• OS: macOS
• Koanf Version 1.3.3

[knadh]

This behaviour is by design. The merge is on the keys recursively (which causes map values to be merged) until a key is traversed to the end to a static non-map value, when the values are overwritten. So, if strings, ints, bools etc. are overwritten ("merged"), it would be counterintuitive for slices to be expanded. The merge behaviour is for key paths from one source into another and not their values.

Example:
a = ["foo", "bar"] + b = ["bar"]

Should it be ["foo", "bar"] (de-duplicated) or ["foo", "bar", "bar"]?

Becomes trickier with your example where the slices themselves can contain arbitrary nesting of slices and maps.

[aeneasr]

Thank you @knadh for the quick reply :) As this is coming from concrete use cases, how would you approach solving the case described in #126 (comment) with Koanf? :)