Add test case to override interface type

Author: ozraru

decode_test.go

@@ -1940,6 +1940,35 @@ func TestDecoder_CustomUnmarshaler(t *testing.T) {
 			t.Fatalf("failed to switch to custom unmarshaler. got: %q", v.Foo)
 		}
 	})
+
+	t.Run("override interface type", func(t *testing.T) {
+		type I interface{}
+		type T struct {
+			Foo string `yaml:"foo"`
+		}
+		var i I
+		src := []byte(`foo: "bar"`)
+		if err := yaml.UnmarshalWithOptions(src, &i, yaml.CustomUnmarshaler[I](func(dst *I, b []byte) error {
+			var v T
+			if err := yaml.Unmarshal(b, &v); err != nil {
+				t.Fatal(err)
+			}
+			if v.Foo != "bar" {
+				t.Fatalf("failed to use unmarshal function. got %q", v.Foo)
+			}
+			*dst = &v
+			return nil
+		})); err != nil {
+			t.Fatal(err)
+		}
+		if v, ok := i.(*T); ok {
+			if v.Foo != "bar" {
+				t.Fatalf("failed to decode with custom interface unmarshaler. got: %q", v.Foo)
+			}
+		} else {
+			t.Fatalf("failed to switch to custom interface unmarshaler.")
+		}
+	})
 }
 
 func TestDecoder_CustomInterfaceUnmarshaler(t *testing.T) {
@@ -1989,6 +2018,35 @@ func TestDecoder_CustomInterfaceUnmarshaler(t *testing.T) {
 			t.Fatalf("failed to switch to custom interface unmarshaler. got: %q", v.Foo)
 		}
 	})
+
+	t.Run("override interface type", func(t *testing.T) {
+		type I interface{}
+		type T struct {
+			Foo string `yaml:"foo"`
+		}
+		var i I
+		src := []byte(`foo: "bar"`)
+		if err := yaml.UnmarshalWithOptions(src, &i, yaml.CustomInterfaceUnmarshaler[I](func(dst *I, f func(interface{}) error) error {
+			var v T
+			if err := f(&v); err != nil {
+				t.Fatal(err)
+			}
+			if v.Foo != "bar" {
+				t.Fatalf("failed to use unmarshal function. got %q", v.Foo)
+			}
+			*dst = &v
+			return nil
+		})); err != nil {
+			t.Fatal(err)
+		}
+		if v, ok := i.(*T); ok {
+			if v.Foo != "bar" {
+				t.Fatalf("failed to decode with custom interface unmarshaler. got: %q", v.Foo)
+			}
+		} else {
+			t.Fatalf("failed to switch to custom interface unmarshaler.")
+		}
+	})
 }
 
 type unmarshalContext struct {