use experimental go json v2 library (#35392)

details: https://pkg.go.dev/encoding/json/v2

---------

Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/json/jsonv2.go

@@ -0,0 +1,92 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build goexperiment.jsonv2
+
+package json
+
+import (
+	"bytes"
+	jsonv1 "encoding/json"    //nolint:depguard // this package wraps it
+	jsonv2 "encoding/json/v2" //nolint:depguard // this package wraps it
+	"io"
+)
+
+// JSONv2 implements Interface via encoding/json/v2
+// Requires GOEXPERIMENT=jsonv2 to be set at build time
+type JSONv2 struct {
+	marshalOptions                  jsonv2.Options
+	marshalKeepOptionalEmptyOptions jsonv2.Options
+	unmarshalOptions                jsonv2.Options
+	unmarshalCaseInsensitiveOptions jsonv2.Options
+}
+
+var jsonV2 JSONv2
+
+func init() {
+	commonMarshalOptions := []jsonv2.Options{
+		jsonv2.FormatNilSliceAsNull(true),
+		jsonv2.FormatNilMapAsNull(true),
+	}
+	jsonV2.marshalOptions = jsonv2.JoinOptions(commonMarshalOptions...)
+	jsonV2.unmarshalOptions = jsonv2.DefaultOptionsV2()
+
+	// By default, "json/v2" omitempty removes all `""` empty strings, no matter where it comes from.
+	// v1 has a different behavior: if the `""` is from a null pointer, or a Marshal function, it is kept.
+	// Golang issue: https://github.com/golang/go/issues/75623 encoding/json/v2: unable to make omitempty work with pointer or Optional type with goexperiment.jsonv2
+	jsonV2.marshalKeepOptionalEmptyOptions = jsonv2.JoinOptions(append(commonMarshalOptions, jsonv1.OmitEmptyWithLegacySemantics(true))...)
+
+	// Some legacy code uses case-insensitive matching (for example: parsing oci.ImageConfig)
+	jsonV2.unmarshalCaseInsensitiveOptions = jsonv2.JoinOptions(jsonv2.MatchCaseInsensitiveNames(true))
+}
+
+func getDefaultJSONHandler() Interface {
+	return &jsonV2
+}
+
+func MarshalKeepOptionalEmpty(v any) ([]byte, error) {
+	return jsonv2.Marshal(v, jsonV2.marshalKeepOptionalEmptyOptions)
+}
+
+func (j *JSONv2) Marshal(v any) ([]byte, error) {
+	return jsonv2.Marshal(v, j.marshalOptions)
+}
+
+func (j *JSONv2) Unmarshal(data []byte, v any) error {
+	return jsonv2.Unmarshal(data, v, j.unmarshalOptions)
+}
+
+func (j *JSONv2) NewEncoder(writer io.Writer) Encoder {
+	return &jsonV2Encoder{writer: writer, opts: j.marshalOptions}
+}
+
+func (j *JSONv2) NewDecoder(reader io.Reader) Decoder {
+	return &jsonV2Decoder{reader: reader, opts: j.unmarshalOptions}
+}
+
+// Indent implements Interface using standard library (JSON v2 doesn't have Indent yet)
+func (*JSONv2) Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error {
+	return jsonv1.Indent(dst, src, prefix, indent)
+}
+
+type jsonV2Encoder struct {
+	writer io.Writer
+	opts   jsonv2.Options
+}
+
+func (e *jsonV2Encoder) Encode(v any) error {
+	return jsonv2.MarshalWrite(e.writer, v, e.opts)
+}
+
+type jsonV2Decoder struct {
+	reader io.Reader
+	opts   jsonv2.Options
+}
+
+func (d *jsonV2Decoder) Decode(v any) error {
+	return jsonv2.UnmarshalRead(d.reader, v, d.opts)
+}
+
+func NewDecoderCaseInsensitive(reader io.Reader) Decoder {
+	return &jsonV2Decoder{reader: reader, opts: jsonV2.unmarshalCaseInsensitiveOptions}
+}