Merge pull request #97 from imdario/pr-85

Overwrite struct's field with corresponding map's key that is intended to be zero

issue84_test.go

@@ -0,0 +1,82 @@
+package mergo
+
+import (
+	"testing"
+)
+
+type DstStructIssue84 struct {
+	A int
+	B int
+	C int
+}
+
+type DstNestedStructIssue84 struct {
+	A struct {
+		A int
+		B int
+		C int
+	}
+	B int
+	C int
+}
+
+func TestIssue84MergeMapWithNilValueToStructWithOverride(t *testing.T) {
+	p1 := DstStructIssue84{
+		A: 0, B: 1, C: 2,
+	}
+	p2 := map[string]interface{}{
+		"A": 3, "B": 4, "C": 0,
+	}
+	if err := Map(&p1, p2, WithOverride); err != nil {
+		t.Fatalf("Error during the merge: %v", err)
+	}
+	if p1.C != 0 {
+		t.Error("C field should become '0'")
+	}
+}
+
+func TestIssue84MergeMapWithoutKeyExistsToStructWithOverride(t *testing.T) {
+	p1 := DstStructIssue84{
+		A: 0, B: 1, C: 2,
+	}
+	p2 := map[string]interface{}{
+		"A": 3, "B": 4,
+	}
+	if err := Map(&p1, p2, WithOverride); err != nil {
+		t.Fatalf("Error during the merge: %v", err)
+	}
+	if p1.C != 2 {
+		t.Error("C field should be '2'")
+	}
+}
+
+func TestIssue84MergeNestedMapWithNilValueToStructWithOverride(t *testing.T) {
+	p1 := DstNestedStructIssue84{
+		A: struct {
+			A int
+			B int
+			C int
+		}{A: 1, B: 2, C: 0},
+		B: 0,
+		C: 2,
+	}
+	p2 := map[string]interface{}{
+		"A": map[string]interface{}{
+			"A": 0, "B": 0, "C": 5,
+		}, "B": 4, "C": 0,
+	}
+	if err := Map(&p1, p2, WithOverride); err != nil {
+		t.Fatalf("Error during the merge: %v", err)
+	}
+	if p1.B != 4 {
+		t.Error("A.C field should become '4'")
+	}
+
+	if p1.A.C != 5 {
+		t.Error("A.C field should become '5'")
+	}
+
+	if p1.A.B != 0 || p1.A.A != 0 {
+		t.Error("A.A and A.B field should become '0'")
+	}
+}

map.go

@@ -72,6 +72,7 @@ func deepMap(dst, src reflect.Value, visited map[uintptr]*visit, depth int, conf
 	case reflect.Struct:
 		srcMap := src.Interface().(map[string]interface{})
 		for key := range srcMap {
+			config.overwriteWithEmptyValue = true
 			srcValue := srcMap[key]
 			fieldName := changeInitialCase(key, unicode.ToUpper)
 			dstElement := dst.FieldByName(fieldName)

merge.go

@@ -26,9 +26,10 @@ func hasExportedField(dst reflect.Value) (exported bool) {
 }
 
 type Config struct {
-	Overwrite    bool
-	AppendSlice  bool
-	Transformers Transformers
+	Overwrite               bool
+	AppendSlice             bool
+	Transformers            Transformers
+	overwriteWithEmptyValue bool
 }
 
 type Transformers interface {
@@ -40,6 +41,8 @@ type Transformers interface {
 // short circuiting on recursive types.
 func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int, config *Config) (err error) {
 	overwrite := config.Overwrite
+	overwriteWithEmptySrc := config.overwriteWithEmptyValue
+	config.overwriteWithEmptyValue = false
 
 	if !src.IsValid() {
 		return
@@ -74,7 +77,7 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int, co
 				}
 			}
 		} else {
-			if dst.CanSet() && !isEmptyValue(src) && (overwrite || isEmptyValue(dst)) {
+			if dst.CanSet() && (!isEmptyValue(src) || overwriteWithEmptySrc) && (overwrite || isEmptyValue(dst)) {
 				dst.Set(src)
 			}
 		}
@@ -125,7 +128,7 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int, co
 						dstSlice = reflect.ValueOf(dstElement.Interface())
 					}
 
-					if !isEmptyValue(src) && (overwrite || isEmptyValue(dst)) && !config.AppendSlice {
+					if (!isEmptyValue(src) || overwriteWithEmptySrc) && (overwrite || isEmptyValue(dst)) && !config.AppendSlice {
 						dstSlice = srcSlice
 					} else if config.AppendSlice {
 						if srcSlice.Type() != dstSlice.Type() {
@@ -151,7 +154,7 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int, co
 		if !dst.CanSet() {
 			break
 		}
-		if !isEmptyValue(src) && (overwrite || isEmptyValue(dst)) && !config.AppendSlice {
+		if (!isEmptyValue(src) || overwriteWithEmptySrc) && (overwrite || isEmptyValue(dst)) && !config.AppendSlice {
 			dst.Set(src)
 		} else if config.AppendSlice {
 			if src.Type() != dst.Type() {
@@ -191,7 +194,7 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int, co
 			return
 		}
 	default:
-		if dst.CanSet() && !isEmptyValue(src) && (overwrite || isEmptyValue(dst)) {
+		if dst.CanSet() && (!isEmptyValue(src) || overwriteWithEmptySrc) && (overwrite || isEmptyValue(dst)) {
 			dst.Set(src)
 		}
 	}