fix(generic): honor mapstructure tags during realization

Author: Oxidaner

filter/generic/generalizer/map.go

@@ -68,7 +68,15 @@ func (g *MapGeneralizer) Realize(obj any, typ reflect.Type) (any, error) {
 		obj = removeClass(obj)
 	}
 	newobj := reflect.New(typ).Interface()
-	err := mapstructure.Decode(obj, newobj)
+	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
+		Result:  newobj,
+		TagName: "mapstructure",
+	})
+	if err != nil {
+		return nil, perrors.Errorf("creating map decoder failed, %v", err)
+	}
+
+	err = decoder.Decode(obj)
 	if err != nil {
 		return nil, perrors.Errorf("realizing map failed, %v", err)
 	}
@@ -249,7 +257,7 @@ func mapKey(key reflect.Value) any {
 // setInMap sets the struct into the map using the tag or the name of the struct as the key
 func setInMap(m map[string]any, structField reflect.StructField, value any) (result map[string]any) {
 	result = m
-	if tagName := structField.Tag.Get("m"); tagName == "" {
+	if tagName := structField.Tag.Get("mapstructure"); tagName == "" {
 		result[toUnexport(structField.Name)] = value
 	} else {
 		result[tagName] = value

filter/generic/generalizer/map_test.go

@@ -35,20 +35,25 @@ import (
 )
 
 type testPlainObj struct {
-	AaAa string `m:"aaAa"`
+	AaAa string `mapstructure:"aaAa"`
 	BaBa string
 	CaCa struct {
 		AaAa string
-		BaBa string `m:"baBa"`
+		BaBa string `mapstructure:"baBa"`
 		XxYy struct {
-			xxXx string `m:"xxXx"`
-			Xx   string `m:"xx"`
-		} `m:"xxYy"`
-	} `m:"caCa"`
+			xxXx string `mapstructure:"xxXx"`
+			Xx   string `mapstructure:"xx"`
+		} `mapstructure:"xxYy"`
+	} `mapstructure:"caCa"`
 	DaDa time.Time
 	EeEe int
 }
 
+type testMapstructureTagObj struct {
+	UserID string `mapstructure:"user_id"`
+	Name   string
+}
+
 func TestObjToMap(t *testing.T) {
 	obj := &testPlainObj{}
 	obj.AaAa = "1"
@@ -71,20 +76,37 @@ func TestObjToMap(t *testing.T) {
 	assert.Equal(t, 100, m["eeEe"].(int))
 }
 
+func TestMapstructureTagRoundTrip(t *testing.T) {
+	original := testMapstructureTagObj{
+		UserID: "42",
+		Name:   "alice",
+	}
+
+	generalized, err := mockMapGeneralizer.Generalize(original)
+	require.NoError(t, err)
+	generalizedMap, ok := generalized.(map[string]any)
+	require.True(t, ok)
+	assert.Equal(t, "42", generalizedMap["user_id"])
+
+	realized, err := mockMapGeneralizer.Realize(generalized, reflect.TypeOf(original))
+	require.NoError(t, err)
+	assert.Equal(t, original, realized)
+}
+
 type testStruct struct {
 	AaAa string
-	BaBa string `m:"baBa"`
+	BaBa string `mapstructure:"baBa"`
 	XxYy struct {
-		xxXx string `m:"xxXx"`
-		Xx   string `m:"xx"`
-	} `m:"xxYy"`
+		xxXx string `mapstructure:"xxXx"`
+		Xx   string `mapstructure:"xx"`
+	} `mapstructure:"xxYy"`
 }
 
 func TestObjToMap_Slice(t *testing.T) {
 	var testData struct {
-		AaAa string `m:"aaAa"`
+		AaAa string `mapstructure:"aaAa"`
 		BaBa string
-		CaCa []testStruct `m:"caCa"`
+		CaCa []testStruct `mapstructure:"caCa"`
 	}
 	testData.AaAa = "1"
 	testData.BaBa = "1"