Repository: imdario/mergo (go)

Issue:
Mergo is not overriding destination map key with empty value with WithOverwriteWithEmptyValue
When trying to merge two maps, mergo does not respect`WithOverwriteWithEmptyValue`.

Eg:

```
destination := map[string]string{"a": "valueOfA"}
source := map[string]string{"b": "valueOfB", "c": "valueOfC"}

mergo.Merge(&destination, &source, mergo.WithOverwriteWithEmptyValue)
```

Current output:
`map[a:valueOfA b:valueOfB c:valueOfC]`

Expected output:
`map[b:valueOfB c:valueOfC]`
Since "a" should be discarded with provided `WithOverwriteWithEmptyValue` option.

Playground: https://go.dev/play/p/kR8K-G7sPPt

Pull request description:
fix: Respect overwriteWithEmptySrc when merging maps
Fixes #230.

Bug originally identified in https://github.com/pulumi/pulumi-kubernetes/issues/2331.

Patch:
diff --git a/merge.go b/merge.go
index 4b47d0b..1bf26cf 100644
--- a/merge.go
+++ b/merge.go
@@ -205,6 +205,16 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int, co
 				dst.SetMapIndex(key, srcElement)
 			}
 		}
+
+		// Ensure that all keys in dst are deleted if they are not in src.
+		if overwriteWithEmptySrc {
+			for _, key := range dst.MapKeys() {
+				srcElement := src.MapIndex(key)
+				if !srcElement.IsValid() {
+					dst.SetMapIndex(key, reflect.Value{})
+				}
+			}
+		}
 	case reflect.Slice:
 		if !dst.CanSet() {
 			break


Test patch:
diff --git a/issue230_test.go b/issue230_test.go
new file mode 100644
index 0000000..129f037
--- /dev/null
+++ b/issue230_test.go
@@ -0,0 +1,85 @@
+package mergo_test
+
+import (
+	"testing"
+
+	"github.com/imdario/mergo"
+)
+
+var testDataM = []struct {
+	M1                     mapTest
+	M2                     mapTest
+	WithOverrideEmptyValue bool
+	ExpectedMap            map[int]int
+}{
+	{
+		M1: mapTest{
+			M: map[int]int{1: 1, 3: 3},
+		},
+		M2: mapTest{
+			M: map[int]int{1: 2, 2: 2},
+		},
+		WithOverrideEmptyValue: true,
+		ExpectedMap:            map[int]int{1: 1, 3: 3},
+	},
+	{
+		M1: mapTest{
+			M: map[int]int{1: 1, 3: 3},
+		},
+		M2: mapTest{
+			M: map[int]int{1: 2, 2: 2},
+		},
+		WithOverrideEmptyValue: false,
+		ExpectedMap:            map[int]int{1: 1, 2: 2, 3: 3},
+	},
+	{
+		M1: mapTest{
+			M: map[int]int{},
+		},
+		M2: mapTest{
+			M: map[int]int{1: 2, 2: 2},
+		},
+		WithOverrideEmptyValue: true,
+		ExpectedMap:            map[int]int{},
+	},
+	{
+		M1: mapTest{
+			M: map[int]int{},
+		},
+		M2: mapTest{
+			M: map[int]int{1: 2, 2: 2},
+		},
+		WithOverrideEmptyValue: false,
+		ExpectedMap:            map[int]int{1: 2, 2: 2},
+	},
+}
+
+func withOverrideEmptyValue(enable bool) func(*mergo.Config) {
+	if enable {
+		return mergo.WithOverwriteWithEmptyValue
+	}
+
+	return mergo.WithOverride
+}
+
+func TestMergeMapWithOverride(t *testing.T) {
+	t.Parallel()
+
+	for _, data := range testDataM {
+		err := mergo.Merge(&data.M2, data.M1, withOverrideEmptyValue(data.WithOverrideEmptyValue))
+		if err != nil {
+			t.Errorf("Error while merging %s", err)
+		}
+
+		if len(data.M2.M) != len(data.ExpectedMap) {
+			t.Errorf("Got %d elements in map, but expected %d", len(data.M2.M), len(data.ExpectedMap))
+			return
+		}
+
+		for i, val := range data.M2.M {
+			if val != data.ExpectedMap[i] {
+				t.Errorf("Expected value: %d, but got %d while merging map", data.ExpectedMap[i], val)
+			}
+		}
+	}
+}
diff --git a/issue89_test.go b/issue89_test.go
index e47a0df..1e138a9 100644
--- a/issue89_test.go
+++ b/issue89_test.go
@@ -36,10 +36,6 @@ func TestIssue89MergeWithEmptyValue(t *testing.T) {
 		expected interface{}
 		key      string
 	}{
-		{
-			3,
-			"A",
-		},
 		{
 			"",
 			"B",