go-json/internal/encoder/compiler.go

package encoder

import (
	"encoding"
	"encoding/json"
	"fmt"
	"reflect"
	"strings"
	"sync/atomic"
	"unsafe"

	"github.com/goccy/go-json/internal/errors"
	"github.com/goccy/go-json/internal/runtime"
)

var (
	marshalJSONType  = reflect.TypeOf((*json.Marshaler)(nil)).Elem()
	marshalTextType  = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
	jsonNumberType   = reflect.TypeOf(json.Number(""))
	cachedOpcodeSets []*OpcodeSet
	cachedOpcodeMap  unsafe.Pointer // map[uintptr]*OpcodeSet
	typeAddr         = &runtime.TypeAddr{}
)

func init() {
	typeAddr = runtime.AnalyzeTypeAddr()
	cachedOpcodeSets = make([]*OpcodeSet, typeAddr.AddrRange)
}

func loadOpcodeMap() map[uintptr]*OpcodeSet {
	p := atomic.LoadPointer(&cachedOpcodeMap)
	return *(*map[uintptr]*OpcodeSet)(unsafe.Pointer(&p))
}

func storeOpcodeSet(typ uintptr, set *OpcodeSet, m map[uintptr]*OpcodeSet) {
	newOpcodeMap := make(map[uintptr]*OpcodeSet, len(m)+1)
	newOpcodeMap[typ] = set

	for k, v := range m {
		newOpcodeMap[k] = v
	}

	atomic.StorePointer(&cachedOpcodeMap, *(*unsafe.Pointer)(unsafe.Pointer(&newOpcodeMap)))
}

func compileToGetCodeSetSlowPath(typeptr uintptr) (*OpcodeSet, error) {
	opcodeMap := loadOpcodeMap()
	if codeSet, exists := opcodeMap[typeptr]; exists {
		return codeSet, nil
	}

	// noescape trick for header.typ ( reflect.*rtype )
	copiedType := *(**runtime.Type)(unsafe.Pointer(&typeptr))

	code, err := compileHead(&compileContext{
		typ:                      copiedType,
		structTypeToCompiledCode: map[uintptr]*CompiledCode{},
	})
	if err != nil {
		return nil, err
	}
	code = copyOpcode(code)
	codeLength := code.TotalLength()
	codeSet := &OpcodeSet{
		Code:       code,
		CodeLength: codeLength,
	}
	storeOpcodeSet(typeptr, codeSet, opcodeMap)
	return codeSet, nil
}

func compileHead(ctx *compileContext) (*Opcode, error) {
	typ := ctx.typ
	switch {
	case implementsMarshalJSON(typ):
		return compileMarshalJSON(ctx)
	case implementsMarshalText(typ):
		return compileMarshalText(ctx)
	}

	isPtr := false
	orgType := typ
	if typ.Kind() == reflect.Ptr {
		typ = typ.Elem()
		isPtr = true
	}
	switch {
	case implementsMarshalJSON(typ):
		return compileMarshalJSON(ctx)
	case implementsMarshalText(typ):
		return compileMarshalText(ctx)
	}
	if typ.Kind() == reflect.Map {
		if isPtr {
			return compilePtr(ctx.withType(runtime.PtrTo(typ)))
		}
		return compileMap(ctx.withType(typ))
	} else if typ.Kind() == reflect.Struct {
		code, err := compileStruct(ctx.withType(typ), isPtr)
		if err != nil {
			return nil, err
		}
		optimizeStructEnd(code)
		linkRecursiveCode(code)
		return code, nil
	} else if isPtr && typ.Implements(marshalTextType) {
		typ = orgType
	}
	code, err := compile(ctx.withType(typ), isPtr)
	if err != nil {
		return nil, err
	}
	optimizeStructEnd(code)
	linkRecursiveCode(code)
	return code, nil
}

func linkRecursiveCode(c *Opcode) {
	for code := c; code.Op != OpEnd && code.Op != OpStructFieldRecursiveEnd; {
		switch code.Op {
		case OpStructFieldRecursive, OpStructFieldRecursivePtr:
			if code.Jmp.Linked {
				code = code.Next
				continue
			}
			code.Jmp.Code = copyOpcode(code.Jmp.Code)
			c := code.Jmp.Code
			c.End.Next = newEndOp(&compileContext{})
			c.Op = c.Op.PtrHeadToHead()

			beforeLastCode := c.End
			lastCode := beforeLastCode.Next

			lastCode.Idx = beforeLastCode.Idx + uintptrSize
			lastCode.ElemIdx = lastCode.Idx + uintptrSize

			// extend length to alloc slot for elemIdx
			totalLength := uintptr(code.TotalLength() + 1)
			nextTotalLength := uintptr(c.TotalLength() + 1)

			c.End.Next.Op = OpStructFieldRecursiveEnd

			code.Jmp.CurLen = totalLength
			code.Jmp.NextLen = nextTotalLength
			code.Jmp.Linked = true

			linkRecursiveCode(code.Jmp.Code)
			code = code.Next
			continue
		}
		switch code.Op.CodeType() {
		case CodeArrayElem, CodeSliceElem, CodeMapKey:
			code = code.End
		default:
			code = code.Next
		}
	}
}

func optimizeStructEnd(c *Opcode) {
	for code := c; code.Op != OpEnd; {
		if code.Op == OpStructFieldRecursive || code.Op == OpStructFieldRecursivePtr {
			// ignore if exists recursive operation
			return
		}
		switch code.Op.CodeType() {
		case CodeArrayElem, CodeSliceElem, CodeMapKey:
			code = code.End
		default:
			code = code.Next
		}
	}

	for code := c; code.Op != OpEnd; {
		switch code.Op.CodeType() {
		case CodeArrayElem, CodeSliceElem, CodeMapKey:
			code = code.End
		case CodeStructEnd:
			switch code.Op {
			case OpStructEnd:
				prev := code.PrevField
				prevOp := prev.Op.String()
				if strings.Contains(prevOp, "Head") ||
					strings.Contains(prevOp, "Slice") ||
					strings.Contains(prevOp, "Array") ||
					strings.Contains(prevOp, "Map") ||
					strings.Contains(prevOp, "MarshalJSON") ||
					strings.Contains(prevOp, "MarshalText") {
					// not exists field
					code = code.Next
					break
				}
				if prev.Op != prev.Op.FieldToEnd() {
					prev.Op = prev.Op.FieldToEnd()
					prev.Next = code.Next
				}
				code = code.Next
			default:
				code = code.Next
			}
		default:
			code = code.Next
		}
	}
}

func implementsMarshalJSON(typ *runtime.Type) bool {
	if !typ.Implements(marshalJSONType) {
		return false
	}
	if typ.Kind() != reflect.Ptr {
		return true
	}
	// type kind is reflect.Ptr
	if !typ.Elem().Implements(marshalJSONType) {
		return true
	}
	// needs to dereference
	return false
}

func implementsMarshalText(typ *runtime.Type) bool {
	if !typ.Implements(marshalTextType) {
		return false
	}
	if typ.Kind() != reflect.Ptr {
		return true
	}
	// type kind is reflect.Ptr
	if !typ.Elem().Implements(marshalTextType) {
		return true
	}
	// needs to dereference
	return false
}

func compile(ctx *compileContext, isPtr bool) (*Opcode, error) {
	typ := ctx.typ
	switch {
	case implementsMarshalJSON(typ):
		return compileMarshalJSON(ctx)
	case implementsMarshalText(typ):
		return compileMarshalText(ctx)
	}
	switch typ.Kind() {
	case reflect.Ptr:
		return compilePtr(ctx)
	case reflect.Slice:
		elem := typ.Elem()
		if elem.Kind() == reflect.Uint8 {
			p := runtime.PtrTo(elem)
			if !p.Implements(marshalJSONType) && !p.Implements(marshalTextType) {
				return compileBytes(ctx)
			}
		}
		return compileSlice(ctx)
	case reflect.Array:
		return compileArray(ctx)
	case reflect.Map:
		return compileMap(ctx)
	case reflect.Struct:
		return compileStruct(ctx, isPtr)
	case reflect.Interface:
		return compileInterface(ctx)
	case reflect.Int:
		return compileInt(ctx)
	case reflect.Int8:
		return compileInt8(ctx)
	case reflect.Int16:
		return compileInt16(ctx)
	case reflect.Int32:
		return compileInt32(ctx)
	case reflect.Int64:
		return compileInt64(ctx)
	case reflect.Uint:
		return compileUint(ctx)
	case reflect.Uint8:
		return compileUint8(ctx)
	case reflect.Uint16:
		return compileUint16(ctx)
	case reflect.Uint32:
		return compileUint32(ctx)
	case reflect.Uint64:
		return compileUint64(ctx)
	case reflect.Uintptr:
		return compileUint(ctx)
	case reflect.Float32:
		return compileFloat32(ctx)
	case reflect.Float64:
		return compileFloat64(ctx)
	case reflect.String:
		return compileString(ctx)
	case reflect.Bool:
		return compileBool(ctx)
	}
	return nil, &errors.UnsupportedTypeError{Type: runtime.RType2Type(typ)}
}

func convertPtrOp(code *Opcode) OpType {
	ptrHeadOp := code.Op.HeadToPtrHead()
	if code.Op != ptrHeadOp {
		if code.PtrNum > 0 {
			// ptr field and ptr head
			code.PtrNum--
		}
		return ptrHeadOp
	}
	switch code.Op {
	case OpInt:
		return OpIntPtr
	case OpUint:
		return OpUintPtr
	case OpFloat32:
		return OpFloat32Ptr
	case OpFloat64:
		return OpFloat64Ptr
	case OpString:
		return OpStringPtr
	case OpBool:
		return OpBoolPtr
	case OpBytes:
		return OpBytesPtr
	case OpArray:
		return OpArrayPtr
	case OpSlice:
		return OpSlicePtr
	case OpMap:
		return OpMapPtr
	case OpMarshalJSON:
		return OpMarshalJSONPtr
	case OpMarshalText:
		return OpMarshalTextPtr
	case OpInterface:
		return OpInterfacePtr
	case OpStructFieldRecursive:
		return OpStructFieldRecursivePtr
	}
	return code.Op
}

func compileKey(ctx *compileContext) (*Opcode, error) {
	typ := ctx.typ
	switch {
	case implementsMarshalJSON(typ):
		return compileMarshalJSON(ctx)
	case implementsMarshalText(typ):
		return compileMarshalText(ctx)
	}
	switch typ.Kind() {
	case reflect.Ptr:
		return compilePtr(ctx)
	case reflect.Interface:
		return compileInterface(ctx)
	case reflect.String:
		return compileString(ctx)
	case reflect.Int:
		return compileIntString(ctx)
	case reflect.Int8:
		return compileInt8String(ctx)
	case reflect.Int16:
		return compileInt16String(ctx)
	case reflect.Int32:
		return compileInt32String(ctx)
	case reflect.Int64:
		return compileInt64String(ctx)
	case reflect.Uint:
		return compileUintString(ctx)
	case reflect.Uint8:
		return compileUint8String(ctx)
	case reflect.Uint16:
		return compileUint16String(ctx)
	case reflect.Uint32:
		return compileUint32String(ctx)
	case reflect.Uint64:
		return compileUint64String(ctx)
	case reflect.Uintptr:
		return compileUintString(ctx)
	}
	return nil, &errors.UnsupportedTypeError{Type: runtime.RType2Type(typ)}
}

func compilePtr(ctx *compileContext) (*Opcode, error) {
	code, err := compile(ctx.withType(ctx.typ.Elem()), true)
	if err != nil {
		return nil, err
	}
	code.Op = convertPtrOp(code)
	code.PtrNum++
	return code, nil
}

func compileMarshalJSON(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpMarshalJSON)
	typ := ctx.typ
	if !typ.Implements(marshalJSONType) && runtime.PtrTo(typ).Implements(marshalJSONType) {
		code.AddrForMarshaler = true
	}
	ctx.incIndex()
	return code, nil
}

func compileMarshalText(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpMarshalText)
	typ := ctx.typ
	if !typ.Implements(marshalTextType) && runtime.PtrTo(typ).Implements(marshalTextType) {
		code.AddrForMarshaler = true
	}
	ctx.incIndex()
	return code, nil
}

const intSize = 32 << (^uint(0) >> 63)

func compileInt(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpInt)
	code.setMaskAndRshiftNum(intSize)
	ctx.incIndex()
	return code, nil
}

func compileInt8(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpInt)
	code.setMaskAndRshiftNum(8)
	ctx.incIndex()
	return code, nil
}

func compileInt16(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpInt)
	code.setMaskAndRshiftNum(16)
	ctx.incIndex()
	return code, nil
}

func compileInt32(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpInt)
	code.setMaskAndRshiftNum(32)
	ctx.incIndex()
	return code, nil
}

func compileInt64(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpInt)
	code.setMaskAndRshiftNum(64)
	ctx.incIndex()
	return code, nil
}

func compileUint(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUint)
	code.setMaskAndRshiftNum(intSize)
	ctx.incIndex()
	return code, nil
}

func compileUint8(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUint)
	code.setMaskAndRshiftNum(8)
	ctx.incIndex()
	return code, nil
}

func compileUint16(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUint)
	code.setMaskAndRshiftNum(16)
	ctx.incIndex()
	return code, nil
}

func compileUint32(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUint)
	code.setMaskAndRshiftNum(32)
	ctx.incIndex()
	return code, nil
}

func compileUint64(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUint)
	code.setMaskAndRshiftNum(64)
	ctx.incIndex()
	return code, nil
}

func compileIntString(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpIntString)
	code.setMaskAndRshiftNum(intSize)
	ctx.incIndex()
	return code, nil
}

func compileInt8String(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpIntString)
	code.setMaskAndRshiftNum(8)
	ctx.incIndex()
	return code, nil
}

func compileInt16String(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpIntString)
	code.setMaskAndRshiftNum(16)
	ctx.incIndex()
	return code, nil
}

func compileInt32String(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpIntString)
	code.setMaskAndRshiftNum(32)
	ctx.incIndex()
	return code, nil
}

func compileInt64String(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpIntString)
	code.setMaskAndRshiftNum(64)
	ctx.incIndex()
	return code, nil
}

func compileUintString(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUintString)
	code.setMaskAndRshiftNum(intSize)
	ctx.incIndex()
	return code, nil
}

func compileUint8String(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUintString)
	code.setMaskAndRshiftNum(8)
	ctx.incIndex()
	return code, nil
}

func compileUint16String(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUintString)
	code.setMaskAndRshiftNum(16)
	ctx.incIndex()
	return code, nil
}

func compileUint32String(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUintString)
	code.setMaskAndRshiftNum(32)
	ctx.incIndex()
	return code, nil
}

func compileUint64String(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpUintString)
	code.setMaskAndRshiftNum(64)
	ctx.incIndex()
	return code, nil
}

func compileFloat32(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpFloat32)
	ctx.incIndex()
	return code, nil
}

func compileFloat64(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpFloat64)
	ctx.incIndex()
	return code, nil
}

func compileString(ctx *compileContext) (*Opcode, error) {
	var op OpType
	if ctx.typ == runtime.Type2RType(jsonNumberType) {
		op = OpNumber
	} else {
		op = OpString
	}
	code := newOpCode(ctx, op)
	ctx.incIndex()
	return code, nil
}

func compileBool(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpBool)
	ctx.incIndex()
	return code, nil
}

func compileBytes(ctx *compileContext) (*Opcode, error) {
	code := newOpCode(ctx, OpBytes)
	ctx.incIndex()
	return code, nil
}

func compileInterface(ctx *compileContext) (*Opcode, error) {
	code := newInterfaceCode(ctx)
	ctx.incIndex()
	return code, nil
}

func compileSlice(ctx *compileContext) (*Opcode, error) {
	elem := ctx.typ.Elem()
	size := elem.Size()

	header := newSliceHeaderCode(ctx)
	ctx.incIndex()

	code, err := compileSliceElem(ctx.withType(elem).incIndent())
	if err != nil {
		return nil, err
	}

	// header => opcode => elem => end
	//             ^        |
	//             |________|

	elemCode := newSliceElemCode(ctx, header, size)
	ctx.incIndex()

	end := newOpCode(ctx, OpSliceEnd)
	ctx.incIndex()

	header.Elem = elemCode
	header.End = end
	header.Next = code
	code.BeforeLastCode().Next = (*Opcode)(unsafe.Pointer(elemCode))
	elemCode.Next = code
	elemCode.End = end
	return (*Opcode)(unsafe.Pointer(header)), nil
}

func compileSliceElem(ctx *compileContext) (*Opcode, error) {
	typ := ctx.typ
	switch {
	case !typ.Implements(marshalJSONType) && runtime.PtrTo(typ).Implements(marshalJSONType):
		return compileMarshalJSON(ctx)
	case !typ.Implements(marshalTextType) && runtime.PtrTo(typ).Implements(marshalTextType):
		return compileMarshalText(ctx)
	default:
		return compile(ctx, false)
	}
}

func compileArray(ctx *compileContext) (*Opcode, error) {
	typ := ctx.typ
	elem := typ.Elem()
	alen := typ.Len()
	size := elem.Size()

	header := newArrayHeaderCode(ctx, alen)
	ctx.incIndex()

	code, err := compile(ctx.withType(elem).incIndent(), false)
	if err != nil {
		return nil, err
	}
	// header => opcode => elem => end
	//             ^        |
	//             |________|

	elemCode := newArrayElemCode(ctx, header, alen, size)
	ctx.incIndex()

	end := newOpCode(ctx, OpArrayEnd)
	ctx.incIndex()

	header.Elem = elemCode
	header.End = end
	header.Next = code
	code.BeforeLastCode().Next = (*Opcode)(unsafe.Pointer(elemCode))
	elemCode.Next = code
	elemCode.End = end
	return (*Opcode)(unsafe.Pointer(header)), nil
}

func compileMap(ctx *compileContext) (*Opcode, error) {
	// header => code => value => code => key => code => value => code => end
	//                                     ^                       |
	//                                     |_______________________|
	ctx = ctx.incIndent()
	header := newMapHeaderCode(ctx)
	ctx.incIndex()

	typ := ctx.typ
	keyType := ctx.typ.Key()
	keyCode, err := compileKey(ctx.withType(keyType))
	if err != nil {
		return nil, err
	}

	value := newMapValueCode(ctx, header)
	ctx.incIndex()

	valueCode, err := compileMapValue(ctx.withType(typ.Elem()))
	if err != nil {
		return nil, err
	}

	key := newMapKeyCode(ctx, header)
	ctx.incIndex()

	ctx = ctx.decIndent()

	header.MapKey = key
	header.MapValue = value

	end := newMapEndCode(ctx, header)
	ctx.incIndex()

	header.Next = keyCode
	keyCode.BeforeLastCode().Next = (*Opcode)(unsafe.Pointer(value))
	value.Next = valueCode
	valueCode.BeforeLastCode().Next = (*Opcode)(unsafe.Pointer(key))
	key.Next = keyCode

	header.End = end
	key.End = end
	value.End = end

	return (*Opcode)(unsafe.Pointer(header)), nil
}

func compileMapValue(ctx *compileContext) (*Opcode, error) {
	switch ctx.typ.Kind() {
	case reflect.Map:
		return compilePtr(ctx.withType(runtime.PtrTo(ctx.typ)))
	default:
		return compile(ctx, false)
	}
}

func optimizeStructHeader(code *Opcode, tag *runtime.StructTag) OpType {
	headType := code.ToHeaderType()
	switch {
	case tag.IsOmitEmpty:
		headType = headType.HeadToOmitEmptyHead()
	case tag.IsString:
		headType = headType.HeadToStringTagHead()
	}
	return headType
}

func optimizeStructField(code *Opcode, tag *runtime.StructTag) OpType {
	fieldType := code.ToFieldType()
	switch {
	case tag.IsOmitEmpty:
		fieldType = fieldType.FieldToOmitEmptyField()
	case tag.IsString:
		fieldType = fieldType.FieldToStringTagField()
	}
	return fieldType
}

func recursiveCode(ctx *compileContext, jmp *CompiledCode) *Opcode {
	code := newRecursiveCode(ctx, jmp)
	ctx.incIndex()
	return code
}

func compiledCode(ctx *compileContext) *Opcode {
	typ := ctx.typ
	typeptr := uintptr(unsafe.Pointer(typ))
	if cc, exists := ctx.structTypeToCompiledCode[typeptr]; exists {
		return recursiveCode(ctx, cc)
	}
	return nil
}

func structHeader(ctx *compileContext, fieldCode *Opcode, valueCode *Opcode, tag *runtime.StructTag) *Opcode {
	fieldCode.Indent--
	op := optimizeStructHeader(valueCode, tag)
	fieldCode.Op = op
	fieldCode.Mask = valueCode.Mask
	fieldCode.RshiftNum = valueCode.RshiftNum
	fieldCode.PtrNum = valueCode.PtrNum
	if op.IsMultipleOpHead() {
		return valueCode.BeforeLastCode()
	}
	ctx.decOpcodeIndex()
	return (*Opcode)(unsafe.Pointer(fieldCode))
}

func structField(ctx *compileContext, fieldCode *Opcode, valueCode *Opcode, tag *runtime.StructTag) *Opcode {
	code := (*Opcode)(unsafe.Pointer(fieldCode))
	op := optimizeStructField(valueCode, tag)
	fieldCode.Op = op
	fieldCode.PtrNum = valueCode.PtrNum
	fieldCode.Mask = valueCode.Mask
	fieldCode.RshiftNum = valueCode.RshiftNum
	fieldCode.Jmp = valueCode.Jmp
	if op.IsMultipleOpField() {
		return valueCode.BeforeLastCode()
	}
	ctx.decIndex()
	return code
}

func isNotExistsField(head *Opcode) bool {
	if head == nil {
		return false
	}
	if head.Op != OpStructHead {
		return false
	}
	if !head.AnonymousHead {
		return false
	}
	if head.Next == nil {
		return false
	}
	if head.NextField == nil {
		return false
	}
	if head.NextField.Op != OpStructAnonymousEnd {
		return false
	}
	if head.Next.Op == OpStructAnonymousEnd {
		return true
	}
	if head.Next.Op.CodeType() != CodeStructField {
		return false
	}
	return isNotExistsField(head.Next)
}

func optimizeAnonymousFields(head *Opcode) {
	code := head
	var prev *Opcode
	removedFields := map[*Opcode]struct{}{}
	for {
		if code.Op == OpStructEnd {
			break
		}
		if code.Op == OpStructField {
			codeType := code.Next.Op.CodeType()
			if codeType == CodeStructField {
				if isNotExistsField(code.Next) {
					code.Next = code.NextField
					diff := code.Next.DisplayIdx - code.DisplayIdx
					for i := 0; i < diff; i++ {
						code.Next.decOpcodeIndex()
					}
					linkPrevToNextField(code, removedFields)
					code = prev
				}
			}
		}
		prev = code
		code = code.NextField
	}
}

type structFieldPair struct {
	prevField   *Opcode
	curField    *Opcode
	isTaggedKey bool
	linked      bool
}

func anonymousStructFieldPairMap(tags runtime.StructTags, named string, valueCode *Opcode) map[string][]structFieldPair {
	anonymousFields := map[string][]structFieldPair{}
	f := valueCode
	var prevAnonymousField *Opcode
	removedFields := map[*Opcode]struct{}{}
	for {
		existsKey := tags.ExistsKey(f.DisplayKey)
		isHeadOp := strings.Contains(f.Op.String(), "Head")
		if existsKey && strings.Contains(f.Op.String(), "Recursive") {
			// through
		} else if isHeadOp && !f.AnonymousHead {
			if existsKey {
				// TODO: need to remove this head
				f.Op = OpStructHead
				f.AnonymousKey = true
				f.AnonymousHead = true
			} else if named == "" {
				f.AnonymousHead = true
			}
		} else if named == "" && f.Op == OpStructEnd {
			f.Op = OpStructAnonymousEnd
		} else if existsKey {
			diff := f.NextField.DisplayIdx - f.DisplayIdx
			for i := 0; i < diff; i++ {
				f.NextField.decOpcodeIndex()
			}
			linkPrevToNextField(f, removedFields)
		}

		if f.DisplayKey == "" {
			if f.NextField == nil {
				break
			}
			prevAnonymousField = f
			f = f.NextField
			continue
		}

		key := fmt.Sprintf("%s.%s", named, f.DisplayKey)
		anonymousFields[key] = append(anonymousFields[key], structFieldPair{
			prevField:   prevAnonymousField,
			curField:    f,
			isTaggedKey: f.IsTaggedKey,
		})
		if f.Next != nil && f.NextField != f.Next && f.Next.Op.CodeType() == CodeStructField {
			for k, v := range anonymousFieldPairRecursively(named, f.Next) {
				anonymousFields[k] = append(anonymousFields[k], v...)
			}
		}
		if f.NextField == nil {
			break
		}
		prevAnonymousField = f
		f = f.NextField
	}
	return anonymousFields
}

func anonymousFieldPairRecursively(named string, valueCode *Opcode) map[string][]structFieldPair {
	anonymousFields := map[string][]structFieldPair{}
	f := valueCode
	var prevAnonymousField *Opcode
	for {
		if f.DisplayKey != "" && f.AnonymousHead {
			key := fmt.Sprintf("%s.%s", named, f.DisplayKey)
			anonymousFields[key] = append(anonymousFields[key], structFieldPair{
				prevField:   prevAnonymousField,
				curField:    f,
				isTaggedKey: f.IsTaggedKey,
			})
			if f.Next != nil && f.NextField != f.Next && f.Next.Op.CodeType() == CodeStructField {
				for k, v := range anonymousFieldPairRecursively(named, f.Next) {
					anonymousFields[k] = append(anonymousFields[k], v...)
				}
			}
		}
		if f.NextField == nil {
			break
		}
		prevAnonymousField = f
		f = f.NextField
	}
	return anonymousFields
}

func optimizeConflictAnonymousFields(anonymousFields map[string][]structFieldPair) {
	removedFields := map[*Opcode]struct{}{}
	for _, fieldPairs := range anonymousFields {
		if len(fieldPairs) == 1 {
			continue
		}
		// conflict anonymous fields
		taggedPairs := []structFieldPair{}
		for _, fieldPair := range fieldPairs {
			if fieldPair.isTaggedKey {
				taggedPairs = append(taggedPairs, fieldPair)
			} else {
				if !fieldPair.linked {
					if fieldPair.prevField == nil {
						// head operation
						fieldPair.curField.Op = OpStructHead
						fieldPair.curField.AnonymousHead = true
						fieldPair.curField.AnonymousKey = true
					} else {
						diff := fieldPair.curField.NextField.DisplayIdx - fieldPair.curField.DisplayIdx
						for i := 0; i < diff; i++ {
							fieldPair.curField.NextField.decOpcodeIndex()
						}
						removedFields[fieldPair.curField] = struct{}{}
						linkPrevToNextField(fieldPair.curField, removedFields)
					}
					fieldPair.linked = true
				}
			}
		}
		if len(taggedPairs) > 1 {
			for _, fieldPair := range taggedPairs {
				if !fieldPair.linked {
					if fieldPair.prevField == nil {
						// head operation
						fieldPair.curField.Op = OpStructHead
						fieldPair.curField.AnonymousHead = true
						fieldPair.curField.AnonymousKey = true
					} else {
						diff := fieldPair.curField.NextField.DisplayIdx - fieldPair.curField.DisplayIdx
						removedFields[fieldPair.curField] = struct{}{}
						for i := 0; i < diff; i++ {
							fieldPair.curField.NextField.decOpcodeIndex()
						}
						linkPrevToNextField(fieldPair.curField, removedFields)
					}
					fieldPair.linked = true
				}
			}
		} else {
			for _, fieldPair := range taggedPairs {
				fieldPair.curField.IsTaggedKey = false
			}
		}
	}
}

func isNilableType(typ *runtime.Type) bool {
	switch typ.Kind() {
	case reflect.Ptr:
		return true
	case reflect.Interface:
		return true
	case reflect.Slice:
		return true
	case reflect.Map:
		return true
	default:
		return false
	}
}

func compileStruct(ctx *compileContext, isPtr bool) (*Opcode, error) {
	if code := compiledCode(ctx); code != nil {
		return code, nil
	}
	typ := ctx.typ
	typeptr := uintptr(unsafe.Pointer(typ))
	compiled := &CompiledCode{}
	ctx.structTypeToCompiledCode[typeptr] = compiled
	// header => code => structField => code => end
	//                        ^          |
	//                        |__________|
	fieldNum := typ.NumField()
	indirect := runtime.IfaceIndir(typ)
	fieldIdx := 0
	disableIndirectConversion := false
	var (
		head      *Opcode
		code      *Opcode
		prevField *Opcode
	)
	ctx = ctx.incIndent()
	tags := runtime.StructTags{}
	anonymousFields := map[string][]structFieldPair{}
	for i := 0; i < fieldNum; i++ {
		field := typ.Field(i)
		if runtime.IsIgnoredStructField(field) {
			continue
		}
		tags = append(tags, runtime.StructTagFromField(field))
	}
	for i, tag := range tags {
		field := tag.Field
		fieldType := runtime.Type2RType(field.Type)
		fieldOpcodeIndex := ctx.opcodeIndex
		fieldPtrIndex := ctx.ptrIndex
		ctx.incIndex()

		nilcheck := true
		addrForMarshaler := false
		isIndirectSpecialCase := isPtr && i == 0 && fieldNum == 1
		isNilableType := isNilableType(fieldType)

		var valueCode *Opcode
		switch {
		case isIndirectSpecialCase && !isNilableType && isPtrMarshalJSONType(fieldType):
			// *struct{ field T } => struct { field *T }
			// func (*T) MarshalJSON() ([]byte, error)
			// move pointer position from head to first field
			code, err := compileMarshalJSON(ctx.withType(runtime.PtrTo(fieldType)))
			if err != nil {
				return nil, err
			}
			valueCode = code
			nilcheck = false
			indirect = false
			disableIndirectConversion = true
		case isIndirectSpecialCase && !isNilableType && isPtrMarshalTextType(fieldType):
			// *struct{ field T } => struct { field *T }
			// func (*T) MarshalText() ([]byte, error)
			// move pointer position from head to first field
			code, err := compileMarshalText(ctx.withType(runtime.PtrTo(fieldType)))
			if err != nil {
				return nil, err
			}
			valueCode = code
			nilcheck = false
			indirect = false
			disableIndirectConversion = true
		case isPtr && isPtrMarshalJSONType(fieldType):
			// *struct{ field T }
			// func (*T) MarshalJSON() ([]byte, error)
			code, err := compileMarshalJSON(ctx.withType(fieldType))
			if err != nil {
				return nil, err
			}
			addrForMarshaler = true
			nilcheck = false
			valueCode = code
		case isPtr && isPtrMarshalTextType(fieldType):
			// *struct{ field T }
			// func (*T) MarshalText() ([]byte, error)
			code, err := compileMarshalText(ctx.withType(fieldType))
			if err != nil {
				return nil, err
			}
			addrForMarshaler = true
			nilcheck = false
			valueCode = code
		default:
			code, err := compile(ctx.withType(fieldType), isPtr)
			if err != nil {
				return nil, err
			}
			valueCode = code
		}

		if field.Anonymous {
			tagKey := ""
			if tag.IsTaggedKey {
				tagKey = tag.Key
			}
			for k, v := range anonymousStructFieldPairMap(tags, tagKey, valueCode) {
				anonymousFields[k] = append(anonymousFields[k], v...)
			}
			valueCode.decIndent()

			// fix issue144
			if !(isPtr && strings.Contains(valueCode.Op.String(), "Marshal")) {
				valueCode.Indirect = indirect
			}
		} else {
			valueCode.Indirect = indirect
		}
		key := fmt.Sprintf(`"%s":`, tag.Key)
		escapedKey := fmt.Sprintf(`%s:`, string(AppendEscapedString([]byte{}, tag.Key)))
		fieldCode := &Opcode{
			Type:             valueCode.Type,
			DisplayIdx:       fieldOpcodeIndex,
			Idx:              opcodeOffset(fieldPtrIndex),
			Next:             valueCode,
			Indent:           ctx.indent,
			AnonymousKey:     field.Anonymous,
			Key:              []byte(key),
			EscapedKey:       []byte(escapedKey),
			IsTaggedKey:      tag.IsTaggedKey,
			DisplayKey:       tag.Key,
			Offset:           field.Offset,
			Indirect:         indirect,
			Nilcheck:         nilcheck,
			AddrForMarshaler: addrForMarshaler,
		}
		if fieldIdx == 0 {
			fieldCode.HeadIdx = fieldCode.Idx
			code = structHeader(ctx, fieldCode, valueCode, tag)
			head = fieldCode
			prevField = fieldCode
		} else {
			fieldCode.HeadIdx = head.HeadIdx
			code.Next = fieldCode
			code = structField(ctx, fieldCode, valueCode, tag)
			prevField.NextField = fieldCode
			fieldCode.PrevField = prevField
			prevField = fieldCode
		}
		fieldIdx++
	}
	ctx = ctx.decIndent()

	structEndCode := &Opcode{
		Op:     OpStructEnd,
		Type:   nil,
		Indent: ctx.indent,
		Next:   newEndOp(ctx),
	}

	// no struct field
	if head == nil {
		head = &Opcode{
			Op:         OpStructHead,
			Type:       typ,
			DisplayIdx: ctx.opcodeIndex,
			Idx:        opcodeOffset(ctx.ptrIndex),
			HeadIdx:    opcodeOffset(ctx.ptrIndex),
			Indent:     ctx.indent,
			NextField:  structEndCode,
		}
		structEndCode.PrevField = head
		ctx.incIndex()
		code = head
	}

	structEndCode.DisplayIdx = ctx.opcodeIndex
	structEndCode.Idx = opcodeOffset(ctx.ptrIndex)
	ctx.incIndex()

	if prevField != nil && prevField.NextField == nil {
		prevField.NextField = structEndCode
		structEndCode.PrevField = prevField
	}

	head.End = structEndCode
	code.Next = structEndCode
	optimizeConflictAnonymousFields(anonymousFields)
	optimizeAnonymousFields(head)
	ret := (*Opcode)(unsafe.Pointer(head))
	compiled.Code = ret

	delete(ctx.structTypeToCompiledCode, typeptr)

	if !disableIndirectConversion && !head.Indirect && isPtr {
		head.Indirect = true
	}

	return ret, nil
}

func isPtrMarshalJSONType(typ *runtime.Type) bool {
	return !typ.Implements(marshalJSONType) && runtime.PtrTo(typ).Implements(marshalJSONType)
}

func isPtrMarshalTextType(typ *runtime.Type) bool {
	return !typ.Implements(marshalTextType) && runtime.PtrTo(typ).Implements(marshalTextType)
}