Merge pull request #45 from yurishkuro/decode-nil-fix-42

Pass appropriate empty Value to hooks

mapstructure.go

@@ -442,21 +442,26 @@ func (d *Decoder) Decode(input interface{}) error {
 	return err
 }
 
+// isNil returns true if the input is nil or a typed nil pointer.
+func isNil(input interface{}) bool {
+	if input == nil {
+		return true
+	}
+	val := reflect.ValueOf(input)
+	return val.Kind() == reflect.Ptr && val.IsNil()
+}
+
 // Decodes an unknown data type into a specific reflection value.
 func (d *Decoder) decode(name string, input interface{}, outVal reflect.Value) error {
-	var inputVal reflect.Value
-	if input != nil {
-		inputVal = reflect.ValueOf(input)
-
-		// We need to check here if input is a typed nil. Typed nils won't
-		// match the "input == nil" below so we check that here.
-		if inputVal.Kind() == reflect.Ptr && inputVal.IsNil() {
-			input = nil
-		}
+	var (
+		inputVal   = reflect.ValueOf(input)
+		outputKind = getKind(outVal)
+		decodeNil  = d.config.DecodeNil && d.cachedDecodeHook != nil
+	)
+	if isNil(input) {
+		// Typed nils won't match the "input == nil" below, so reset input.
+		input = nil
 	}
-
-	decodeNil := d.config.DecodeNil && d.config.DecodeHook != nil
-
 	if input == nil {
 		// If the data is nil, then we don't set anything, unless ZeroFields is set
 		// to true.
@@ -467,12 +472,10 @@ func (d *Decoder) decode(name string, input interface{}, outVal reflect.Value) e
 				d.config.Metadata.Keys = append(d.config.Metadata.Keys, name)
 			}
 		}
-
 		if !decodeNil {
 			return nil
 		}
 	}
-
 	if !inputVal.IsValid() {
 		if !decodeNil {
 			// If the input value is invalid, then we just set the value
@@ -483,11 +486,17 @@ func (d *Decoder) decode(name string, input interface{}, outVal reflect.Value) e
 			}
 			return nil
 		}
-
-		// If we get here, we have an untyped nil so the type of the input is assumed.
-		// We do this because all subsequent code requires a valid value for inputVal.
-		var mapVal map[string]interface{}
-		inputVal = reflect.MakeMap(reflect.TypeOf(mapVal))
+		// Hooks need a valid inputVal, so reset it to zero value of outVal type.
+		switch outputKind {
+		case reflect.Struct, reflect.Map:
+			var mapVal map[string]interface{}
+			inputVal = reflect.ValueOf(mapVal) // create nil map pointer
+		case reflect.Slice, reflect.Array:
+			var sliceVal []interface{}
+			inputVal = reflect.ValueOf(sliceVal) // create nil slice pointer
+		default:
+			inputVal = reflect.Zero(outVal.Type())
+		}
 	}
 
 	if d.cachedDecodeHook != nil {
@@ -498,9 +507,11 @@ func (d *Decoder) decode(name string, input interface{}, outVal reflect.Value) e
 			return fmt.Errorf("error decoding '%s': %w", name, err)
 		}
 	}
+	if isNil(input) {
+		return nil
+	}
 
 	var err error
-	outputKind := getKind(outVal)
 	addMetaKey := true
 	switch outputKind {
 	case reflect.Bool:
@@ -781,8 +792,8 @@ func (d *Decoder) decodeBool(name string, data interface{}, val reflect.Value) e
 		}
 	default:
 		return fmt.Errorf(
-			"'%s' expected type '%s', got unconvertible type '%s', value: '%v'",
-			name, val.Type(), dataVal.Type(), data)
+			"'%s' expected type '%s', got unconvertible type '%#v', value: '%#v'",
+			name, val, dataVal, data)
 	}
 
 	return nil

mapstructure_test.go

@@ -3083,7 +3083,7 @@ func TestDecoder_IgnoreUntaggedFieldsWithStruct(t *testing.T) {
 	}
 }
 
-func TestDecoder_CanPerformDecodingForNilInputs(t *testing.T) {
+func TestDecoder_DecodeNilOption(t *testing.T) {
 	t.Parallel()
 
 	type Transformed struct {
@@ -3100,6 +3100,9 @@ func TestDecoder_CanPerformDecodingForNilInputs(t *testing.T) {
 	appendHook := func(from reflect.Value, to reflect.Value) (interface{}, error) {
 		if from.Kind() == reflect.Map {
 			stringMap := from.Interface().(map[string]interface{})
+			if stringMap == nil {
+				stringMap = make(map[string]interface{})
+			}
 			stringMap["when"] = "see you later"
 			return stringMap, nil
 		}
@@ -3248,6 +3251,67 @@ func TestDecoder_CanPerformDecodingForNilInputs(t *testing.T) {
 	}
 }
 
+func TestDecoder_ExpandNilStructPointersHookFunc(t *testing.T) {
+	// a decoder hook that expands nil pointers in a struct to their zero value
+	// if the input map contains the corresponding key.
+	decodeHook := func(from reflect.Value, to reflect.Value) (any, error) {
+		if from.Kind() == reflect.Map && to.Kind() == reflect.Map {
+			toElem := to.Type().Elem()
+			if toElem.Kind() == reflect.Ptr && toElem.Elem().Kind() == reflect.Struct {
+				fromRange := from.MapRange()
+				for fromRange.Next() {
+					fromKey := fromRange.Key()
+					fromValue := fromRange.Value()
+					if fromValue.IsNil() {
+						newFromValue := reflect.New(toElem.Elem())
+						from.SetMapIndex(fromKey, newFromValue)
+					}
+				}
+			}
+		}
+		return from.Interface(), nil
+	}
+	type Struct struct {
+		Name string
+	}
+	type TestConfig struct {
+		Boolean   *bool              `mapstructure:"boolean"`
+		Struct    *Struct            `mapstructure:"struct"`
+		MapStruct map[string]*Struct `mapstructure:"map_struct"`
+	}
+	stringMap := map[string]any{
+		"boolean": nil,
+		"struct":  nil,
+		"map_struct": map[string]any{
+			"struct": nil,
+		},
+	}
+	var result TestConfig
+	decoder, err := NewDecoder(&DecoderConfig{
+		Result:     &result,
+		DecodeNil:  true,
+		DecodeHook: decodeHook,
+	})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	if err := decoder.Decode(stringMap); err != nil {
+		t.Fatalf("got an err: %s", err)
+	}
+	if result.Boolean != nil {
+		t.Errorf("nil Boolean expected, got '%#v'", result.Boolean)
+	}
+	if result.Struct != nil {
+		t.Errorf("nil Struct expected, got '%#v'", result.Struct)
+	}
+	if len(result.MapStruct) == 0 {
+		t.Fatalf("not-empty MapStruct expected, got '%#v'", result.MapStruct)
+	}
+	if _, ok := result.MapStruct["struct"]; !ok {
+		t.Errorf("MapStruct['struct'] expected")
+	}
+}
+
 func testSliceInput(t *testing.T, input map[string]interface{}, expected *Slice) {
 	var result Slice
 	err := Decode(input, &result)