use experimental go json v2 library

Makefile

@@ -18,6 +18,9 @@ DIST := dist
 DIST_DIRS := $(DIST)/binaries $(DIST)/release
 IMPORT := code.gitea.io/gitea
 
+# No experiment set by default, but you can set jsonv2 to use go 1.25.0 json v2 experimental changes
+export GOEXPERIMENT ?=
+
 GO ?= go
 SHASUM ?= shasum -a 256
 HAS_GO := $(shell hash $(GO) > /dev/null 2>&1 && echo yes)

modules/json/json.go

@@ -32,13 +32,22 @@ type Interface interface {
 }
 
 var (
-	// DefaultJSONHandler default json handler
-	DefaultJSONHandler Interface = JSONiter{jsoniter.ConfigCompatibleWithStandardLibrary}
+	// DefaultJSONHandler default json handler - uses JSON v2 if available, otherwise JSONiter
+	DefaultJSONHandler = getDefaultHandler()
 
 	_ Interface = StdJSON{}
 	_ Interface = JSONiter{}
+	_ Interface = JSONv2{}
 )
 
+// getDefaultHandler returns the expected JSON implementation
+func getDefaultHandler() Interface {
+	if isJSONv2Available() {
+		return JSONv2{}
+	}
+	return JSONiter{jsoniter.ConfigCompatibleWithStandardLibrary}
+}
+
 // StdJSON implements Interface via encoding/json
 type StdJSON struct{}
 
@@ -97,6 +106,47 @@ func (j JSONiter) Indent(dst *bytes.Buffer, src []byte, prefix, indent string) e
 	return json.Indent(dst, src, prefix, indent)
 }
 
+// JSONv2 implements Interface via encoding/json/v2
+// Requires GOEXPERIMENT=jsonv2 to be set at build time
+type JSONv2 struct{}
+
+// Marshal implements Interface using JSON v2 - fallback if v2 is not available
+func (JSONv2) Marshal(v any) ([]byte, error) {
+	if !isJSONv2Available() {
+		return json.Marshal(v)
+	}
+	return marshalV2(v)
+}
+
+// Unmarshal implements Interface using JSON v2 - fallback if v2 is not available
+func (JSONv2) Unmarshal(data []byte, v any) error {
+	if !isJSONv2Available() {
+		return json.Unmarshal(data, v)
+	}
+	return unmarshalV2(data, v)
+}
+
+// NewEncoder implements Interface using JSON v2 - fallback if v2 is not available
+func (JSONv2) NewEncoder(writer io.Writer) Encoder {
+	if !isJSONv2Available() {
+		return json.NewEncoder(writer)
+	}
+	return newEncoderV2(writer)
+}
+
+// NewDecoder implements Interface using JSON v2 - fallback if v2 is not available
+func (JSONv2) NewDecoder(reader io.Reader) Decoder {
+	if !isJSONv2Available() {
+		return json.NewDecoder(reader)
+	}
+	return newDecoderV2(reader)
+}
+
+// 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 json.Indent(dst, src, prefix, indent)
+}
+
 // Marshal converts object as bytes
 func Marshal(v any) ([]byte, error) {
 	return DefaultJSONHandler.Marshal(v)

modules/json/jsonv2.go

@@ -0,0 +1,72 @@
+//go:build goexperiment.jsonv2
+
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package json
+
+import (
+	jsonv2 "encoding/json/v2"
+	"io"
+)
+
+// isJSONv2Available returns true when JSON v2 is available (compiled with GOEXPERIMENT=jsonv2)
+func isJSONv2Available() bool {
+	return true
+}
+
+// marshalV2 uses JSON v2 marshal with v1 compatibility options
+func marshalV2(v any) ([]byte, error) {
+	opts := jsonv2.JoinOptions(
+		jsonv2.MatchCaseInsensitiveNames(true),
+		jsonv2.FormatNilSliceAsNull(true),
+		jsonv2.FormatNilMapAsNull(true),
+	)
+	return jsonv2.Marshal(v, opts)
+}
+
+// unmarshalV2 uses JSON v2 unmarshal with v1 compatibility options
+func unmarshalV2(data []byte, v any) error {
+	opts := jsonv2.JoinOptions(
+		jsonv2.MatchCaseInsensitiveNames(true),
+	)
+	return jsonv2.Unmarshal(data, v, opts)
+}
+
+// encoderV2 wraps JSON v2 streaming encoder
+type encoderV2 struct {
+	writer io.Writer
+	opts   jsonv2.Options
+}
+
+func (e *encoderV2) Encode(v any) error {
+	return jsonv2.MarshalWrite(e.writer, v, e.opts)
+}
+
+// newEncoderV2 creates a new JSON v2 streaming encoder
+func newEncoderV2(writer io.Writer) Encoder {
+	opts := jsonv2.JoinOptions(
+		jsonv2.MatchCaseInsensitiveNames(true),
+		jsonv2.FormatNilSliceAsNull(true),
+		jsonv2.FormatNilMapAsNull(true),
+	)
+	return &encoderV2{writer: writer, opts: opts}
+}
+
+// decoderV2 wraps JSON v2 streaming decoder
+type decoderV2 struct {
+	reader io.Reader
+	opts   jsonv2.Options
+}
+
+func (d *decoderV2) Decode(v any) error {
+	return jsonv2.UnmarshalRead(d.reader, v, d.opts)
+}
+
+// newDecoderV2 creates a new JSON v2 streaming decoder
+func newDecoderV2(reader io.Reader) Decoder {
+	opts := jsonv2.JoinOptions(
+		jsonv2.MatchCaseInsensitiveNames(true),
+	)
+	return &decoderV2{reader: reader, opts: opts}
+}

modules/json/jsonv2_fallback.go

@@ -0,0 +1,33 @@
+//go:build !goexperiment.jsonv2
+
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package json
+
+import "io"
+
+// isJSONv2Available returns false when JSON v2 is not available (not compiled with GOEXPERIMENT=jsonv2)
+func isJSONv2Available() bool {
+	return false
+}
+
+// marshalV2 fallback - should not be called when JSON v2 is not available
+func marshalV2(v any) ([]byte, error) {
+	panic("JSON v2 not available - build with GOEXPERIMENT=jsonv2")
+}
+
+// unmarshalV2 fallback - should not be called when JSON v2 is not available
+func unmarshalV2(data []byte, v any) error {
+	panic("JSON v2 not available - build with GOEXPERIMENT=jsonv2")
+}
+
+// newEncoderV2 fallback - should not be called when JSON v2 is not available
+func newEncoderV2(writer io.Writer) Encoder {
+	panic("JSON v2 not available - build with GOEXPERIMENT=jsonv2")
+}
+
+// newDecoderV2 fallback - should not be called when JSON v2 is not available
+func newDecoderV2(reader io.Reader) Decoder {
+	panic("JSON v2 not available - build with GOEXPERIMENT=jsonv2")
+}