V2 [WIP]

go.work

@@ -0,0 +1,6 @@
+go 1.20
+
+use (
+	.
+	./v2
+)

mergo_test.go

@@ -6,7 +6,7 @@
 package mergo_test
 
 import (
-	"io/ioutil"
+	"os"
 	"reflect"
 	"strings"
 	"testing"
@@ -846,7 +846,7 @@ func TestNestedPtrValueInMap(t *testing.T) {
 
 func loadYAML(path string) (m map[string]interface{}) {
 	m = make(map[string]interface{})
-	raw, _ := ioutil.ReadFile(path)
+	raw, _ := os.ReadFile(path)
 	_ = yaml.Unmarshal(raw, &m)
 	return
 }

v2/addressables_test.go

@@ -0,0 +1,45 @@
+package mergo_test
+
+import (
+	"testing"
+
+	"dario.cat/mergo/v2"
+)
+
+func litPtr[T any](v T) *T {
+	return &v
+}
+
+func TestIntMerge(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		dst  *int
+		src  int
+		want *int
+	}{
+		{dst: litPtr(0), src: 1, want: litPtr(1)},
+		{dst: litPtr(2), src: 1, want: litPtr(2)},
+		{dst: nil, src: 1, want: nil},
+		{dst: litPtr(3), src: 0, want: litPtr(3)},
+	}
+	for _, tc := range testCases {
+		tc := tc
+
+		t.Run("", func(t *testing.T) {
+			t.Parallel()
+
+			mergo.Merge(tc.dst, tc.src)
+			if tc.dst == nil {
+				if tc.want != nil {
+					t.Errorf("expected %v, got %v", *tc.want, tc.dst)
+				}
+
+				return
+			}
+			if *tc.dst != *tc.want {
+				t.Errorf("expected %v, got %v", *tc.want, *tc.dst)
+			}
+		})
+	}
+}

v2/go.mod

@@ -0,0 +1,5 @@
+module dario.cat/mergo/v2
+
+go 1.20
+
+require github.com/google/go-cmp v0.5.9

v2/go.sum

@@ -0,0 +1,2 @@
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=

v2/merge.go

@@ -0,0 +1,28 @@
+package mergo
+
+import "reflect"
+
+// Merge (WIP) merges src into dst recursively setting src values on dst
+// if src values are not zero values and dst values are zero values.
+// Breaking change: src can't be a T pointer anymore.
+//
+//go:noinline
+func Merge[T any](dst *T, src T) {
+	if dst == nil {
+		return
+	}
+
+	elm := reflect.ValueOf(*dst)
+
+	// If dst is an interface, we need to get the underlying value.
+	if elm.Kind() == reflect.Interface {
+		elm = elm.Elem()
+	}
+
+	// If dst is a non-zero value, we don't need to do anything.
+	if !elm.IsZero() {
+		return
+	}
+
+	*dst = src
+}

v2/unadressables_test.go

@@ -0,0 +1,46 @@
+package mergo_test
+
+import (
+	"testing"
+
+	"dario.cat/mergo/v2"
+	"github.com/google/go-cmp/cmp"
+)
+
+func ifc[T any](v T) interface{} {
+	return v
+}
+
+func TestInterfaceMerge(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		dst  *interface{}
+		src  interface{}
+		want interface{}
+	}{
+		{dst: litPtr(ifc(0)), src: 1, want: 1},
+		{dst: litPtr(ifc(2)), src: 1, want: 2},
+		{dst: nil, src: 1, want: nil},
+		{dst: litPtr(ifc(3)), src: 0, want: 3},
+	}
+	for _, tc := range testCases {
+		tc := tc
+
+		t.Run("", func(t *testing.T) {
+			t.Parallel()
+
+			mergo.Merge(tc.dst, tc.src)
+			if tc.dst == nil {
+				if tc.want != nil {
+					t.Errorf("expected %v, got %v", tc.want, tc.dst)
+				}
+
+				return
+			}
+			if !cmp.Equal(*tc.dst, tc.want) {
+				t.Errorf("expected %v, got %v", tc.want, *tc.dst)
+			}
+		})
+	}
+}