MergeStrict returns the first error

Signed-off-by: Daniel Gront <grount1@gmail.com>

README.md

@@ -564,16 +564,6 @@ func main() {
 
 	jsonPath := "mock/mock.json"
 	if err := k.Load(file.Provider(jsonPath), json.Parser()); err != nil {
-		// go version <= v1.12
-		if strictErr := err.(*maps.MergeStrictError); strictErr != nil {
-			log.Fatalf("error merging config %v: %v", jsonPath, err)
-		}
-		// go version > v1.12
-		var strictErr *maps.MergeStrictError
-		if errors.As(err, &strictErr) {
-			log.Fatalf("error merging config %v: %v", jsonPath, err)
-		}
-
 		log.Fatalf("error loading config: %v", err)
 	}
 }

koanf.go

@@ -68,15 +68,10 @@ type UnmarshalConf struct {
 // when specifying config key paths, for instance a . for `parent.child.key`
 // or a / for `parent/child/key`.
 func New(delim string) *Koanf {
-	return &Koanf{
-		confMap:     make(map[string]interface{}),
-		confMapFlat: make(map[string]interface{}),
-		keyMap:      make(KeyMap),
-		conf: Conf{
-			Delim:       delim,
-			StrictMerge: false,
-		},
-	}
+	return NewWithConf(Conf{
+		Delim: delim,
+		StrictMerge: false,
+	})
 }
 
 // NewWithConf returns a new instance of Koanf based on the Conf.
@@ -393,8 +388,7 @@ func (ko *Koanf) MapKeys(path string) []string {
 func (ko *Koanf) merge(c map[string]interface{}) error{
 	maps.IntfaceKeysToStrings(c)
 	if ko.conf.StrictMerge {
-		err := maps.MergeStrict(c, ko.confMap)
-		if err != nil {
+		if err := maps.MergeStrict(c, ko.confMap); err != nil {
 			return err
 		}
 	} else {

koanf_test.go

@@ -14,7 +14,6 @@ import (
 	"time"
 
 	"github.com/knadh/koanf"
-	"github.com/knadh/koanf/maps"
 	"github.com/knadh/koanf/parsers/dotenv"
 	"github.com/knadh/koanf/parsers/hcl"
 	"github.com/knadh/koanf/parsers/json"
@@ -735,7 +734,6 @@ func TestMergeStrictError(t *testing.T) {
 
 	err := ks.Load(file.Provider(mockYAML), yaml.Parser())
 	assert.Error(err)
-	assert.IsType(&maps.MergeStrictError{}, err)
 	assert.True(strings.HasPrefix(err.Error(), "incorrect types at key parent2.child2.grandchild2"))
 }
 

maps/maps.go

@@ -10,17 +10,6 @@ import (
 	"strings"
 )
 
-type MergeStrictError struct {
-	Errors []error
-}
-
-func (m *MergeStrictError) Error() string {
-	var msg string
-	for _, err := range m.Errors {
-		msg += fmt.Sprintf("%v\n", err.Error())
-	}
-	return msg
-}
 
 // Flatten takes a map[string]interface{} and traverses it and flattens
 // nested children into keys delimited by delim.
@@ -145,16 +134,19 @@ func Merge(a, b map[string]interface{}) {
 	}
 }
 
+// MergeStrict recursively merges map a into b (left to right), mutating
+// and expanding map b. Note that there's no copying involved, so
+// map b will retain references to map a.
+// If an equal key in either of the maps has a different value type, it will return the first error.
+//
+// It's important to note that all nested maps should be
+// map[string]interface{} and not map[interface{}]interface{}.
+// Use IntfaceKeysToStrings() to convert if necessary.
 func MergeStrict(a, b map[string]interface{}) error {
-	mergeError := MergeStrictError{Errors: []error{}}
-	mergeStrict(a, b, &mergeError, "")
-	if len(mergeError.Errors) > 0 {
-		return &mergeError
-	}
-	return nil
+	return mergeStrict(a, b, "")
 }
 
-func mergeStrict(a, b map[string]interface{}, mergeError *MergeStrictError, fullKey string) {
+func mergeStrict(a, b map[string]interface{}, fullKey string) error {
 	for key, val := range a {
 		// Does the key exist in the target map?
 		// If no, add it and move on.
@@ -174,20 +166,20 @@ func mergeStrict(a, b map[string]interface{}, mergeError *MergeStrictError, full
 			if reflect.TypeOf(b[key]) == reflect.TypeOf(val) {
 				b[key] = val
 			} else {
-				err := fmt.Errorf("incorrect types at key %v, type %T != %T", fullKey, b[key], val)
-				mergeError.Errors = append(mergeError.Errors, err)
+				return fmt.Errorf("incorrect types at key %v, type %T != %T", fullKey, b[key], val)
 			}
 			continue
 		}
 
 		// The source key and target keys are both maps. Merge them.
 		switch v := bVal.(type) {
 		case map[string]interface{}:
-			mergeStrict(val.(map[string]interface{}), v, mergeError, newFullKey)
+			return mergeStrict(val.(map[string]interface{}), v, newFullKey)
 		default:
 			b[key] = val
 		}
 	}
+	return nil
 }
 
 // Delete removes the entry present at a given path, from the map. The path