Update filter to use json package interfaces.

filters/filter.go

@@ -111,7 +111,7 @@ func WithExtension(l string, e json.RawMessage) FilterOption {
 
 // MarshalJSON converts the filter to JSON with standard fields, tag filters
 // (prefixed with "#"), and extensions merged into a single object.
-func MarshalJSON(f Filter) ([]byte, error) {
+func (f Filter) MarshalJSON() ([]byte, error) {
 	outputMap := make(map[string]interface{})
 
 	// Add standard fields
@@ -168,7 +168,7 @@ func MarshalJSON(f Filter) ([]byte, error) {
 
 // UnmarshalJSON parses JSON into the filter, separating standard fields,
 // tag filters (keys starting with "#"), and extensions.
-func UnmarshalJSON(data []byte, f *Filter) error {
+func (f *Filter) UnmarshalJSON(data []byte) error {
 	// Decode into raw map
 	raw := make(FilterExtensions)
 	if err := json.Unmarshal(data, &raw); err != nil {

filters/filter_json_test.go

@@ -547,7 +547,7 @@ var roundTripTestCases = []FilterRoundTripTestCase{
 func TestFilterMarshalJSON(t *testing.T) {
 	for _, tc := range marshalTestCases {
 		t.Run(tc.name, func(t *testing.T) {
-			result, err := MarshalJSON(tc.filter)
+			result, err := json.Marshal(tc.filter)
 			assert.NoError(t, err)
 
 			var expectedMap, actualMap map[string]interface{}
@@ -565,7 +565,7 @@ func TestFilterUnmarshalJSON(t *testing.T) {
 	for _, tc := range unmarshalTestCases {
 		t.Run(tc.name, func(t *testing.T) {
 			var result Filter
-			err := UnmarshalJSON([]byte(tc.input), &result)
+			err := json.Unmarshal([]byte(tc.input), &result)
 			assert.NoError(t, err)
 
 			expectEqualFilters(t, result, tc.expected)
@@ -576,11 +576,11 @@ func TestFilterUnmarshalJSON(t *testing.T) {
 func TestFilterRoundTrip(t *testing.T) {
 	for _, tc := range roundTripTestCases {
 		t.Run(tc.name, func(t *testing.T) {
-			jsonBytes, err := MarshalJSON(tc.filter)
+			jsonBytes, err := json.Marshal(tc.filter)
 			assert.NoError(t, err)
 
 			var result Filter
-			err = UnmarshalJSON(jsonBytes, &result)
+			err = json.Unmarshal(jsonBytes, &result)
 			assert.NoError(t, err)
 
 			expectEqualFilters(t, result, tc.filter)