internal/impl/legacy_message.go - protobuf - Git at Google

 // Copyright 2018 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package impl

 import (
 	"fmt"
 	"reflect"
 	"strings"
 	"sync"

 	"google.golang.org/protobuf/internal/descopts"
 	ptag "google.golang.org/protobuf/internal/encoding/tag"
 	"google.golang.org/protobuf/internal/errors"
 	"google.golang.org/protobuf/internal/filedesc"
 	"google.golang.org/protobuf/internal/strs"
 	"google.golang.org/protobuf/reflect/protoreflect"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/runtime/protoiface"
 	piface "google.golang.org/protobuf/runtime/protoiface"
 )

 // legacyWrapMessage wraps v as a protoreflect.Message,
 // where v must be a *struct kind and not implement the v2 API already.
 func legacyWrapMessage(v reflect.Value) pref.Message {
 	typ := v.Type()
 	if typ.Kind() != reflect.Ptr || typ.Elem().Kind() != reflect.Struct {
 		return aberrantMessage{v: v}
 	}
 	mt := legacyLoadMessageInfo(typ, "")
 	return mt.MessageOf(v.Interface())
 }

 // legacyLoadMessageType dynamically loads a protoreflect.Type for t,
 // where t must be not implement the v2 API already.
 // The provided name is used if it cannot be determined from the message.
 func legacyLoadMessageType(t reflect.Type, name pref.FullName) protoreflect.MessageType {
 	if t.Kind() != reflect.Ptr || t.Elem().Kind() != reflect.Struct {
 		return aberrantMessageType{t}
 	}
 	return legacyLoadMessageInfo(t, name)
 }

 var legacyMessageTypeCache sync.Map // map[reflect.Type]*MessageInfo

 // legacyLoadMessageInfo dynamically loads a *MessageInfo for t,
 // where t must be a *struct kind and not implement the v2 API already.
 // The provided name is used if it cannot be determined from the message.
 func legacyLoadMessageInfo(t reflect.Type, name pref.FullName) *MessageInfo {
 	// Fast-path: check if a MessageInfo is cached for this concrete type.
 	if mt, ok := legacyMessageTypeCache.Load(t); ok {
 		return mt.(*MessageInfo)
 	}

 	// Slow-path: derive message descriptor and initialize MessageInfo.
 	mi := &MessageInfo{
 		Desc:          legacyLoadMessageDesc(t, name),
 		GoReflectType: t,
 	}

 	v := reflect.Zero(t).Interface()
 	if _, ok := v.(legacyMarshaler); ok {
 		mi.methods.Marshal = legacyMarshal

 		// We have no way to tell whether the type's Marshal method
 		// supports deterministic serialization or not, but this
 		// preserves the v1 implementation's behavior of always
 		// calling Marshal methods when present.
 		mi.methods.Flags |= piface.SupportMarshalDeterministic
 	}
 	if _, ok := v.(legacyUnmarshaler); ok {
 		mi.methods.Unmarshal = legacyUnmarshal
 	}
 	if _, ok := v.(legacyMerger); ok {
 		mi.methods.Merge = legacyMerge
 	}

 	if mi, ok := legacyMessageTypeCache.LoadOrStore(t, mi); ok {
 		return mi.(*MessageInfo)
 	}
 	return mi
 }

 var legacyMessageDescCache sync.Map // map[reflect.Type]protoreflect.MessageDescriptor

 // LegacyLoadMessageDesc returns an MessageDescriptor derived from the Go type,
 // which must be a *struct kind and not implement the v2 API already.
 //
 // This is exported for testing purposes.
 func LegacyLoadMessageDesc(t reflect.Type) pref.MessageDescriptor {
 	return legacyLoadMessageDesc(t, "")
 }
 func legacyLoadMessageDesc(t reflect.Type, name pref.FullName) pref.MessageDescriptor {
 	// Fast-path: check if a MessageDescriptor is cached for this concrete type.
 	if mi, ok := legacyMessageDescCache.Load(t); ok {
 		return mi.(pref.MessageDescriptor)
 	}

 	// Slow-path: initialize MessageDescriptor from the raw descriptor.
 	mv := reflect.Zero(t).Interface()
 	if _, ok := mv.(pref.ProtoMessage); ok {
 		panic(fmt.Sprintf("%v already implements proto.Message", t))
 	}
 	mdV1, ok := mv.(messageV1)
 	if !ok {
 		return aberrantLoadMessageDesc(t, name)
 	}

 	// If this is a dynamic message type where there isn't a 1-1 mapping between
 	// Go and protobuf types, calling the Descriptor method on the zero value of
 	// the message type isn't likely to work. If it panics, swallow the panic and
 	// continue as if the Descriptor method wasn't present.
 	b, idxs := func() ([]byte, []int) {
 		defer func() {
 			recover()
 		}()
 		return mdV1.Descriptor()
 	}()
 	if b == nil {
 		return aberrantLoadMessageDesc(t, name)
 	}

 	// If the Go type has no fields, then this might be a proto3 empty message
 	// from before the size cache was added. If there are any fields, check to
 	// see that at least one of them looks like something we generated.
 	if nfield := t.Elem().NumField(); nfield > 0 {
 		hasProtoField := false
 		for i := 0; i < nfield; i++ {
 			f := t.Elem().Field(i)
 			if f.Tag.Get("protobuf") != "" || f.Tag.Get("protobuf_oneof") != "" || strings.HasPrefix(f.Name, "XXX_") {
 				hasProtoField = true
 				break
 			}
 		}
 		if !hasProtoField {
 			return aberrantLoadMessageDesc(t, name)
 		}
 	}

 	md := legacyLoadFileDesc(b).Messages().Get(idxs[0])
 	for _, i := range idxs[1:] {
 		md = md.Messages().Get(i)
 	}
 	if name != "" && md.FullName() != name {
 		panic(fmt.Sprintf("mismatching message name: got %v, want %v", md.FullName(), name))
 	}
 	if md, ok := legacyMessageDescCache.LoadOrStore(t, md); ok {
 		return md.(protoreflect.MessageDescriptor)
 	}
 	return md
 }

 var (
 	aberrantMessageDescLock  sync.Mutex
 	aberrantMessageDescCache map[reflect.Type]protoreflect.MessageDescriptor
 )

 // aberrantLoadMessageDesc returns an MessageDescriptor derived from the Go type,
 // which must not implement protoreflect.ProtoMessage or messageV1.
 //
 // This is a best-effort derivation of the message descriptor using the protobuf
 // tags on the struct fields.
 func aberrantLoadMessageDesc(t reflect.Type, name pref.FullName) pref.MessageDescriptor {
 	aberrantMessageDescLock.Lock()
 	defer aberrantMessageDescLock.Unlock()
 	if aberrantMessageDescCache == nil {
 		aberrantMessageDescCache = make(map[reflect.Type]protoreflect.MessageDescriptor)
 	}
 	return aberrantLoadMessageDescReentrant(t, name)
 }
 func aberrantLoadMessageDescReentrant(t reflect.Type, name pref.FullName) pref.MessageDescriptor {
 	// Fast-path: check if an MessageDescriptor is cached for this concrete type.
 	if md, ok := aberrantMessageDescCache[t]; ok {
 		return md
 	}

 	// Slow-path: construct a descriptor from the Go struct type (best-effort).
 	// Cache the MessageDescriptor early on so that we can resolve internal
 	// cyclic references.
 	md := &filedesc.Message{L2: new(filedesc.MessageL2)}
 	md.L0.FullName = aberrantDeriveMessageName(t, name)
 	md.L0.ParentFile = filedesc.SurrogateProto2
 	aberrantMessageDescCache[t] = md

 	if t.Kind() != reflect.Ptr || t.Elem().Kind() != reflect.Struct {
 		return md
 	}

 	// Try to determine if the message is using proto3 by checking scalars.
 	for i := 0; i < t.Elem().NumField(); i++ {
 		f := t.Elem().Field(i)
 		if tag := f.Tag.Get("protobuf"); tag != "" {
 			switch f.Type.Kind() {
 			case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String:
 				md.L0.ParentFile = filedesc.SurrogateProto3
 			}
 			for _, s := range strings.Split(tag, ",") {
 				if s == "proto3" {
 					md.L0.ParentFile = filedesc.SurrogateProto3
 				}
 			}
 		}
 	}

 	// Obtain a list of oneof wrapper types.
 	var oneofWrappers []reflect.Type
 	for _, method := range []string{"XXX_OneofFuncs", "XXX_OneofWrappers"} {
 		if fn, ok := t.MethodByName(method); ok {
 			for _, v := range fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))}) {
 				if vs, ok := v.Interface().([]interface{}); ok {
 					for _, v := range vs {
 						oneofWrappers = append(oneofWrappers, reflect.TypeOf(v))
 					}
 				}
 			}
 		}
 	}

 	// Obtain a list of the extension ranges.
 	if fn, ok := t.MethodByName("ExtensionRangeArray"); ok {
 		vs := fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))})[0]
 		for i := 0; i < vs.Len(); i++ {
 			v := vs.Index(i)
 			md.L2.ExtensionRanges.List = append(md.L2.ExtensionRanges.List, [2]pref.FieldNumber{
 				pref.FieldNumber(v.FieldByName("Start").Int()),
 				pref.FieldNumber(v.FieldByName("End").Int() + 1),
 			})
 			md.L2.ExtensionRangeOptions = append(md.L2.ExtensionRangeOptions, nil)
 		}
 	}

 	// Derive the message fields by inspecting the struct fields.
 	for i := 0; i < t.Elem().NumField(); i++ {
 		f := t.Elem().Field(i)
 		if tag := f.Tag.Get("protobuf"); tag != "" {
 			tagKey := f.Tag.Get("protobuf_key")
 			tagVal := f.Tag.Get("protobuf_val")
 			aberrantAppendField(md, f.Type, tag, tagKey, tagVal)
 		}
 		if tag := f.Tag.Get("protobuf_oneof"); tag != "" {
 			n := len(md.L2.Oneofs.List)
 			md.L2.Oneofs.List = append(md.L2.Oneofs.List, filedesc.Oneof{})
 			od := &md.L2.Oneofs.List[n]
 			od.L0.FullName = md.FullName().Append(pref.Name(tag))
 			od.L0.ParentFile = md.L0.ParentFile
 			od.L0.Parent = md
 			od.L0.Index = n

 			for _, t := range oneofWrappers {
 				if t.Implements(f.Type) {
 					f := t.Elem().Field(0)
 					if tag := f.Tag.Get("protobuf"); tag != "" {
 						aberrantAppendField(md, f.Type, tag, "", "")
 						fd := &md.L2.Fields.List[len(md.L2.Fields.List)-1]
 						fd.L1.ContainingOneof = od
 						od.L1.Fields.List = append(od.L1.Fields.List, fd)
 					}
 				}
 			}
 		}
 	}

 	return md
 }

 func aberrantDeriveMessageName(t reflect.Type, name pref.FullName) pref.FullName {
 	if name.IsValid() {
 		return name
 	}
 	func() {
 		defer func() { recover() }() // swallow possible nil panics
 		if m, ok := reflect.Zero(t).Interface().(interface{ XXX_MessageName() string }); ok {
 			name = pref.FullName(m.XXX_MessageName())
 		}
 	}()
 	if name.IsValid() {
 		return name
 	}
 	if t.Kind() == reflect.Ptr {
 		t = t.Elem()
 	}
 	return AberrantDeriveFullName(t)
 }

 func aberrantAppendField(md *filedesc.Message, goType reflect.Type, tag, tagKey, tagVal string) {
 	t := goType
 	isOptional := t.Kind() == reflect.Ptr && t.Elem().Kind() != reflect.Struct
 	isRepeated := t.Kind() == reflect.Slice && t.Elem().Kind() != reflect.Uint8
 	if isOptional || isRepeated {
 		t = t.Elem()
 	}
 	fd := ptag.Unmarshal(tag, t, placeholderEnumValues{}).(*filedesc.Field)

 	// Append field descriptor to the message.
 	n := len(md.L2.Fields.List)
 	md.L2.Fields.List = append(md.L2.Fields.List, *fd)
 	fd = &md.L2.Fields.List[n]
 	fd.L0.FullName = md.FullName().Append(fd.Name())
 	fd.L0.ParentFile = md.L0.ParentFile
 	fd.L0.Parent = md
 	fd.L0.Index = n

 	if fd.L1.IsWeak || fd.L1.HasPacked {
 		fd.L1.Options = func() pref.ProtoMessage {
 			opts := descopts.Field.ProtoReflect().New()
 			if fd.L1.IsWeak {
 				opts.Set(opts.Descriptor().Fields().ByName("weak"), protoreflect.ValueOfBool(true))
 			}
 			if fd.L1.HasPacked {
 				opts.Set(opts.Descriptor().Fields().ByName("packed"), protoreflect.ValueOfBool(fd.L1.IsPacked))
 			}
 			return opts.Interface()
 		}
 	}

 	// Populate Enum and Message.
 	if fd.Enum() == nil && fd.Kind() == pref.EnumKind {
 		switch v := reflect.Zero(t).Interface().(type) {
 		case pref.Enum:
 			fd.L1.Enum = v.Descriptor()
 		default:
 			fd.L1.Enum = LegacyLoadEnumDesc(t)
 		}
 	}
 	if fd.Message() == nil && (fd.Kind() == pref.MessageKind || fd.Kind() == pref.GroupKind) {
 		switch v := reflect.Zero(t).Interface().(type) {
 		case pref.ProtoMessage:
 			fd.L1.Message = v.ProtoReflect().Descriptor()
 		case messageV1:
 			fd.L1.Message = LegacyLoadMessageDesc(t)
 		default:
 			if t.Kind() == reflect.Map {
 				n := len(md.L1.Messages.List)
 				md.L1.Messages.List = append(md.L1.Messages.List, filedesc.Message{L2: new(filedesc.MessageL2)})
 				md2 := &md.L1.Messages.List[n]
 				md2.L0.FullName = md.FullName().Append(pref.Name(strs.MapEntryName(string(fd.Name()))))
 				md2.L0.ParentFile = md.L0.ParentFile
 				md2.L0.Parent = md
 				md2.L0.Index = n

 				md2.L1.IsMapEntry = true
 				md2.L2.Options = func() pref.ProtoMessage {
 					opts := descopts.Message.ProtoReflect().New()
 					opts.Set(opts.Descriptor().Fields().ByName("map_entry"), protoreflect.ValueOfBool(true))
 					return opts.Interface()
 				}

 				aberrantAppendField(md2, t.Key(), tagKey, "", "")
 				aberrantAppendField(md2, t.Elem(), tagVal, "", "")

 				fd.L1.Message = md2
 				break
 			}
 			fd.L1.Message = aberrantLoadMessageDescReentrant(t, "")
 		}
 	}
 }

 type placeholderEnumValues struct {
 	protoreflect.EnumValueDescriptors
 }

 func (placeholderEnumValues) ByNumber(n pref.EnumNumber) pref.EnumValueDescriptor {
 	return filedesc.PlaceholderEnumValue(pref.FullName(fmt.Sprintf("UNKNOWN_%d", n)))
 }

 // legacyMarshaler is the proto.Marshaler interface superseded by protoiface.Methoder.
 type legacyMarshaler interface {
 	Marshal() ([]byte, error)
 }

 // legacyUnmarshaler is the proto.Unmarshaler interface superseded by protoiface.Methoder.
 type legacyUnmarshaler interface {
 	Unmarshal([]byte) error
 }

 // legacyMerger is the proto.Merger interface superseded by protoiface.Methoder.
 type legacyMerger interface {
 	Merge(protoiface.MessageV1)
 }

 var aberrantProtoMethods = &piface.Methods{
 	Marshal:   legacyMarshal,
 	Unmarshal: legacyUnmarshal,
 	Merge:     legacyMerge,

 	// We have no way to tell whether the type's Marshal method
 	// supports deterministic serialization or not, but this
 	// preserves the v1 implementation's behavior of always
 	// calling Marshal methods when present.
 	Flags: piface.SupportMarshalDeterministic,
 }

 func legacyMarshal(in piface.MarshalInput) (piface.MarshalOutput, error) {
 	v := in.Message.(unwrapper).protoUnwrap()
 	marshaler, ok := v.(legacyMarshaler)
 	if !ok {
 		return piface.MarshalOutput{}, errors.New("%T does not implement Marshal", v)
 	}
 	out, err := marshaler.Marshal()
 	if in.Buf != nil {
 		out = append(in.Buf, out...)
 	}
 	return piface.MarshalOutput{
 		Buf: out,
 	}, err
 }

 func legacyUnmarshal(in piface.UnmarshalInput) (piface.UnmarshalOutput, error) {
 	v := in.Message.(unwrapper).protoUnwrap()
 	unmarshaler, ok := v.(legacyUnmarshaler)
 	if !ok {
 		return piface.UnmarshalOutput{}, errors.New("%T does not implement Marshal", v)
 	}
 	return piface.UnmarshalOutput{}, unmarshaler.Unmarshal(in.Buf)
 }

 func legacyMerge(in piface.MergeInput) piface.MergeOutput {
 	dstv := in.Destination.(unwrapper).protoUnwrap()
 	merger, ok := dstv.(legacyMerger)
 	if !ok {
 		return piface.MergeOutput{}
 	}
 	merger.Merge(Export{}.ProtoMessageV1Of(in.Source))
 	return piface.MergeOutput{Flags: piface.MergeComplete}
 }

 // aberrantMessageType implements MessageType for all types other than pointer-to-struct.
 type aberrantMessageType struct {
 	t reflect.Type
 }

 func (mt aberrantMessageType) New() pref.Message {
 	return aberrantMessage{reflect.Zero(mt.t)}
 }
 func (mt aberrantMessageType) Zero() pref.Message {
 	return aberrantMessage{reflect.Zero(mt.t)}
 }
 func (mt aberrantMessageType) GoType() reflect.Type {
 	return mt.t
 }
 func (mt aberrantMessageType) Descriptor() pref.MessageDescriptor {
 	return LegacyLoadMessageDesc(mt.t)
 }

 // aberrantMessage implements Message for all types other than pointer-to-struct.
 //
 // When the underlying type implements legacyMarshaler or legacyUnmarshaler,
 // the aberrant Message can be marshaled or unmarshaled. Otherwise, there is
 // not much that can be done with values of this type.
 type aberrantMessage struct {
 	v reflect.Value
 }

 func (m aberrantMessage) ProtoReflect() pref.Message {
 	return m
 }

 func (m aberrantMessage) Descriptor() pref.MessageDescriptor {
 	return LegacyLoadMessageDesc(m.v.Type())
 }
 func (m aberrantMessage) Type() pref.MessageType {
 	return aberrantMessageType{m.v.Type()}
 }
 func (m aberrantMessage) New() pref.Message {
 	return aberrantMessage{reflect.Zero(m.v.Type())}
 }
 func (m aberrantMessage) Interface() pref.ProtoMessage {
 	return m
 }
 func (m aberrantMessage) Range(f func(pref.FieldDescriptor, pref.Value) bool) {
 }
 func (m aberrantMessage) Has(pref.FieldDescriptor) bool {
 	panic("invalid field descriptor")
 }
 func (m aberrantMessage) Clear(pref.FieldDescriptor) {
 	panic("invalid field descriptor")
 }
 func (m aberrantMessage) Get(pref.FieldDescriptor) pref.Value {
 	panic("invalid field descriptor")
 }
 func (m aberrantMessage) Set(pref.FieldDescriptor, pref.Value) {
 	panic("invalid field descriptor")
 }
 func (m aberrantMessage) Mutable(pref.FieldDescriptor) pref.Value {
 	panic("invalid field descriptor")
 }
 func (m aberrantMessage) NewField(pref.FieldDescriptor) pref.Value {
 	panic("invalid field descriptor")
 }
 func (m aberrantMessage) WhichOneof(pref.OneofDescriptor) pref.FieldDescriptor {
 	panic("invalid oneof descriptor")
 }
 func (m aberrantMessage) GetUnknown() pref.RawFields {
 	return nil
 }
 func (m aberrantMessage) SetUnknown(pref.RawFields) {
 	// SetUnknown discards its input on messages which don't support unknown field storage.
 }
 func (m aberrantMessage) IsValid() bool {
 	// An invalid message is a read-only, empty message. Since we don't know anything
 	// about the alleged contents of this message, we can't say with confidence that
 	// it is invalid in this sense. Therefore, report it as valid.
 	return true
 }
 func (m aberrantMessage) ProtoMethods() *piface.Methods {
 	return aberrantProtoMethods
 }
 func (m aberrantMessage) protoUnwrap() interface{} {
 	return m.v.Interface()
 }
	// Copyright 2018 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package impl

	import (
	"fmt"
	"reflect"
	"strings"
	"sync"

	"google.golang.org/protobuf/internal/descopts"
	ptag "google.golang.org/protobuf/internal/encoding/tag"
	"google.golang.org/protobuf/internal/errors"
	"google.golang.org/protobuf/internal/filedesc"
	"google.golang.org/protobuf/internal/strs"
	"google.golang.org/protobuf/reflect/protoreflect"
	pref "google.golang.org/protobuf/reflect/protoreflect"
	"google.golang.org/protobuf/runtime/protoiface"
	piface "google.golang.org/protobuf/runtime/protoiface"
	)

	// legacyWrapMessage wraps v as a protoreflect.Message,
	// where v must be a *struct kind and not implement the v2 API already.
	func legacyWrapMessage(v reflect.Value) pref.Message {
	typ := v.Type()
	if typ.Kind() != reflect.Ptr \|\| typ.Elem().Kind() != reflect.Struct {
	return aberrantMessage{v: v}
	}
	mt := legacyLoadMessageInfo(typ, "")
	return mt.MessageOf(v.Interface())
	}

	// legacyLoadMessageType dynamically loads a protoreflect.Type for t,
	// where t must be not implement the v2 API already.
	// The provided name is used if it cannot be determined from the message.
	func legacyLoadMessageType(t reflect.Type, name pref.FullName) protoreflect.MessageType {
	if t.Kind() != reflect.Ptr \|\| t.Elem().Kind() != reflect.Struct {
	return aberrantMessageType{t}
	}
	return legacyLoadMessageInfo(t, name)
	}

	var legacyMessageTypeCache sync.Map // map[reflect.Type]*MessageInfo

	// legacyLoadMessageInfo dynamically loads a *MessageInfo for t,
	// where t must be a *struct kind and not implement the v2 API already.
	// The provided name is used if it cannot be determined from the message.
	func legacyLoadMessageInfo(t reflect.Type, name pref.FullName) *MessageInfo {
	// Fast-path: check if a MessageInfo is cached for this concrete type.
	if mt, ok := legacyMessageTypeCache.Load(t); ok {
	return mt.(*MessageInfo)
	}

	// Slow-path: derive message descriptor and initialize MessageInfo.
	mi := &MessageInfo{
	Desc: legacyLoadMessageDesc(t, name),
	GoReflectType: t,
	}

	v := reflect.Zero(t).Interface()
	if _, ok := v.(legacyMarshaler); ok {
	mi.methods.Marshal = legacyMarshal

	// We have no way to tell whether the type's Marshal method
	// supports deterministic serialization or not, but this
	// preserves the v1 implementation's behavior of always
	// calling Marshal methods when present.
	mi.methods.Flags \|= piface.SupportMarshalDeterministic
	}
	if _, ok := v.(legacyUnmarshaler); ok {
	mi.methods.Unmarshal = legacyUnmarshal
	}
	if _, ok := v.(legacyMerger); ok {
	mi.methods.Merge = legacyMerge
	}

	if mi, ok := legacyMessageTypeCache.LoadOrStore(t, mi); ok {
	return mi.(*MessageInfo)
	}
	return mi
	}

	var legacyMessageDescCache sync.Map // map[reflect.Type]protoreflect.MessageDescriptor

	// LegacyLoadMessageDesc returns an MessageDescriptor derived from the Go type,
	// which must be a *struct kind and not implement the v2 API already.
	//
	// This is exported for testing purposes.
	func LegacyLoadMessageDesc(t reflect.Type) pref.MessageDescriptor {
	return legacyLoadMessageDesc(t, "")
	}
	func legacyLoadMessageDesc(t reflect.Type, name pref.FullName) pref.MessageDescriptor {
	// Fast-path: check if a MessageDescriptor is cached for this concrete type.
	if mi, ok := legacyMessageDescCache.Load(t); ok {
	return mi.(pref.MessageDescriptor)
	}

	// Slow-path: initialize MessageDescriptor from the raw descriptor.
	mv := reflect.Zero(t).Interface()
	if _, ok := mv.(pref.ProtoMessage); ok {
	panic(fmt.Sprintf("%v already implements proto.Message", t))
	}
	mdV1, ok := mv.(messageV1)
	if !ok {
	return aberrantLoadMessageDesc(t, name)
	}

	// If this is a dynamic message type where there isn't a 1-1 mapping between
	// Go and protobuf types, calling the Descriptor method on the zero value of
	// the message type isn't likely to work. If it panics, swallow the panic and
	// continue as if the Descriptor method wasn't present.
	b, idxs := func() ([]byte, []int) {
	defer func() {
	recover()
	}()
	return mdV1.Descriptor()
	}()
	if b == nil {
	return aberrantLoadMessageDesc(t, name)
	}

	// If the Go type has no fields, then this might be a proto3 empty message
	// from before the size cache was added. If there are any fields, check to
	// see that at least one of them looks like something we generated.
	if nfield := t.Elem().NumField(); nfield > 0 {
	hasProtoField := false
	for i := 0; i < nfield; i++ {
	f := t.Elem().Field(i)
	if f.Tag.Get("protobuf") != "" \|\| f.Tag.Get("protobuf_oneof") != "" \|\| strings.HasPrefix(f.Name, "XXX_") {
	hasProtoField = true
	break
	}
	}
	if !hasProtoField {
	return aberrantLoadMessageDesc(t, name)
	}
	}

	md := legacyLoadFileDesc(b).Messages().Get(idxs[0])
	for _, i := range idxs[1:] {
	md = md.Messages().Get(i)
	}
	if name != "" && md.FullName() != name {
	panic(fmt.Sprintf("mismatching message name: got %v, want %v", md.FullName(), name))
	}
	if md, ok := legacyMessageDescCache.LoadOrStore(t, md); ok {
	return md.(protoreflect.MessageDescriptor)
	}
	return md
	}

	var (
	aberrantMessageDescLock sync.Mutex
	aberrantMessageDescCache map[reflect.Type]protoreflect.MessageDescriptor
	)

	// aberrantLoadMessageDesc returns an MessageDescriptor derived from the Go type,
	// which must not implement protoreflect.ProtoMessage or messageV1.
	//
	// This is a best-effort derivation of the message descriptor using the protobuf
	// tags on the struct fields.
	func aberrantLoadMessageDesc(t reflect.Type, name pref.FullName) pref.MessageDescriptor {
	aberrantMessageDescLock.Lock()
	defer aberrantMessageDescLock.Unlock()
	if aberrantMessageDescCache == nil {
	aberrantMessageDescCache = make(map[reflect.Type]protoreflect.MessageDescriptor)
	}
	return aberrantLoadMessageDescReentrant(t, name)
	}
	func aberrantLoadMessageDescReentrant(t reflect.Type, name pref.FullName) pref.MessageDescriptor {
	// Fast-path: check if an MessageDescriptor is cached for this concrete type.
	if md, ok := aberrantMessageDescCache[t]; ok {
	return md
	}

	// Slow-path: construct a descriptor from the Go struct type (best-effort).
	// Cache the MessageDescriptor early on so that we can resolve internal
	// cyclic references.
	md := &filedesc.Message{L2: new(filedesc.MessageL2)}
	md.L0.FullName = aberrantDeriveMessageName(t, name)
	md.L0.ParentFile = filedesc.SurrogateProto2
	aberrantMessageDescCache[t] = md

	if t.Kind() != reflect.Ptr \|\| t.Elem().Kind() != reflect.Struct {
	return md
	}

	// Try to determine if the message is using proto3 by checking scalars.
	for i := 0; i < t.Elem().NumField(); i++ {
	f := t.Elem().Field(i)
	if tag := f.Tag.Get("protobuf"); tag != "" {
	switch f.Type.Kind() {
	case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String:
	md.L0.ParentFile = filedesc.SurrogateProto3
	}
	for _, s := range strings.Split(tag, ",") {
	if s == "proto3" {
	md.L0.ParentFile = filedesc.SurrogateProto3
	}
	}
	}
	}

	// Obtain a list of oneof wrapper types.
	var oneofWrappers []reflect.Type
	for _, method := range []string{"XXX_OneofFuncs", "XXX_OneofWrappers"} {
	if fn, ok := t.MethodByName(method); ok {
	for _, v := range fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))}) {
	if vs, ok := v.Interface().([]interface{}); ok {
	for _, v := range vs {
	oneofWrappers = append(oneofWrappers, reflect.TypeOf(v))
	}
	}
	}
	}
	}

	// Obtain a list of the extension ranges.
	if fn, ok := t.MethodByName("ExtensionRangeArray"); ok {
	vs := fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))})[0]
	for i := 0; i < vs.Len(); i++ {
	v := vs.Index(i)
	md.L2.ExtensionRanges.List = append(md.L2.ExtensionRanges.List, [2]pref.FieldNumber{
	pref.FieldNumber(v.FieldByName("Start").Int()),
	pref.FieldNumber(v.FieldByName("End").Int() + 1),
	})
	md.L2.ExtensionRangeOptions = append(md.L2.ExtensionRangeOptions, nil)
	}
	}

	// Derive the message fields by inspecting the struct fields.
	for i := 0; i < t.Elem().NumField(); i++ {
	f := t.Elem().Field(i)
	if tag := f.Tag.Get("protobuf"); tag != "" {
	tagKey := f.Tag.Get("protobuf_key")
	tagVal := f.Tag.Get("protobuf_val")
	aberrantAppendField(md, f.Type, tag, tagKey, tagVal)
	}
	if tag := f.Tag.Get("protobuf_oneof"); tag != "" {
	n := len(md.L2.Oneofs.List)
	md.L2.Oneofs.List = append(md.L2.Oneofs.List, filedesc.Oneof{})
	od := &md.L2.Oneofs.List[n]
	od.L0.FullName = md.FullName().Append(pref.Name(tag))
	od.L0.ParentFile = md.L0.ParentFile
	od.L0.Parent = md
	od.L0.Index = n

	for _, t := range oneofWrappers {
	if t.Implements(f.Type) {
	f := t.Elem().Field(0)
	if tag := f.Tag.Get("protobuf"); tag != "" {
	aberrantAppendField(md, f.Type, tag, "", "")
	fd := &md.L2.Fields.List[len(md.L2.Fields.List)-1]
	fd.L1.ContainingOneof = od
	od.L1.Fields.List = append(od.L1.Fields.List, fd)
	}
	}
	}
	}
	}

	return md
	}

	func aberrantDeriveMessageName(t reflect.Type, name pref.FullName) pref.FullName {
	if name.IsValid() {
	return name
	}
	func() {
	defer func() { recover() }() // swallow possible nil panics
	if m, ok := reflect.Zero(t).Interface().(interface{ XXX_MessageName() string }); ok {
	name = pref.FullName(m.XXX_MessageName())
	}
	}()
	if name.IsValid() {
	return name
	}
	if t.Kind() == reflect.Ptr {
	t = t.Elem()
	}
	return AberrantDeriveFullName(t)
	}

	func aberrantAppendField(md *filedesc.Message, goType reflect.Type, tag, tagKey, tagVal string) {
	t := goType
	isOptional := t.Kind() == reflect.Ptr && t.Elem().Kind() != reflect.Struct
	isRepeated := t.Kind() == reflect.Slice && t.Elem().Kind() != reflect.Uint8
	if isOptional \|\| isRepeated {
	t = t.Elem()
	}
	fd := ptag.Unmarshal(tag, t, placeholderEnumValues{}).(*filedesc.Field)

	// Append field descriptor to the message.
	n := len(md.L2.Fields.List)
	md.L2.Fields.List = append(md.L2.Fields.List, *fd)
	fd = &md.L2.Fields.List[n]
	fd.L0.FullName = md.FullName().Append(fd.Name())
	fd.L0.ParentFile = md.L0.ParentFile
	fd.L0.Parent = md
	fd.L0.Index = n

	if fd.L1.IsWeak \|\| fd.L1.HasPacked {
	fd.L1.Options = func() pref.ProtoMessage {
	opts := descopts.Field.ProtoReflect().New()
	if fd.L1.IsWeak {
	opts.Set(opts.Descriptor().Fields().ByName("weak"), protoreflect.ValueOfBool(true))
	}
	if fd.L1.HasPacked {
	opts.Set(opts.Descriptor().Fields().ByName("packed"), protoreflect.ValueOfBool(fd.L1.IsPacked))
	}
	return opts.Interface()
	}
	}

	// Populate Enum and Message.
	if fd.Enum() == nil && fd.Kind() == pref.EnumKind {
	switch v := reflect.Zero(t).Interface().(type) {
	case pref.Enum:
	fd.L1.Enum = v.Descriptor()
	default:
	fd.L1.Enum = LegacyLoadEnumDesc(t)
	}
	}
	if fd.Message() == nil && (fd.Kind() == pref.MessageKind \|\| fd.Kind() == pref.GroupKind) {
	switch v := reflect.Zero(t).Interface().(type) {
	case pref.ProtoMessage:
	fd.L1.Message = v.ProtoReflect().Descriptor()
	case messageV1:
	fd.L1.Message = LegacyLoadMessageDesc(t)
	default:
	if t.Kind() == reflect.Map {
	n := len(md.L1.Messages.List)
	md.L1.Messages.List = append(md.L1.Messages.List, filedesc.Message{L2: new(filedesc.MessageL2)})
	md2 := &md.L1.Messages.List[n]
	md2.L0.FullName = md.FullName().Append(pref.Name(strs.MapEntryName(string(fd.Name()))))
	md2.L0.ParentFile = md.L0.ParentFile
	md2.L0.Parent = md
	md2.L0.Index = n

	md2.L1.IsMapEntry = true
	md2.L2.Options = func() pref.ProtoMessage {
	opts := descopts.Message.ProtoReflect().New()
	opts.Set(opts.Descriptor().Fields().ByName("map_entry"), protoreflect.ValueOfBool(true))
	return opts.Interface()
	}

	aberrantAppendField(md2, t.Key(), tagKey, "", "")
	aberrantAppendField(md2, t.Elem(), tagVal, "", "")

	fd.L1.Message = md2
	break
	}
	fd.L1.Message = aberrantLoadMessageDescReentrant(t, "")
	}
	}
	}

	type placeholderEnumValues struct {
	protoreflect.EnumValueDescriptors
	}

	func (placeholderEnumValues) ByNumber(n pref.EnumNumber) pref.EnumValueDescriptor {
	return filedesc.PlaceholderEnumValue(pref.FullName(fmt.Sprintf("UNKNOWN_%d", n)))
	}

	// legacyMarshaler is the proto.Marshaler interface superseded by protoiface.Methoder.
	type legacyMarshaler interface {
	Marshal() ([]byte, error)
	}

	// legacyUnmarshaler is the proto.Unmarshaler interface superseded by protoiface.Methoder.
	type legacyUnmarshaler interface {
	Unmarshal([]byte) error
	}

	// legacyMerger is the proto.Merger interface superseded by protoiface.Methoder.
	type legacyMerger interface {
	Merge(protoiface.MessageV1)
	}

	var aberrantProtoMethods = &piface.Methods{
	Marshal: legacyMarshal,
	Unmarshal: legacyUnmarshal,
	Merge: legacyMerge,

	// We have no way to tell whether the type's Marshal method
	// supports deterministic serialization or not, but this
	// preserves the v1 implementation's behavior of always
	// calling Marshal methods when present.
	Flags: piface.SupportMarshalDeterministic,
	}

	func legacyMarshal(in piface.MarshalInput) (piface.MarshalOutput, error) {
	v := in.Message.(unwrapper).protoUnwrap()
	marshaler, ok := v.(legacyMarshaler)
	if !ok {
	return piface.MarshalOutput{}, errors.New("%T does not implement Marshal", v)
	}
	out, err := marshaler.Marshal()
	if in.Buf != nil {
	out = append(in.Buf, out...)
	}
	return piface.MarshalOutput{
	Buf: out,
	}, err
	}

	func legacyUnmarshal(in piface.UnmarshalInput) (piface.UnmarshalOutput, error) {
	v := in.Message.(unwrapper).protoUnwrap()
	unmarshaler, ok := v.(legacyUnmarshaler)
	if !ok {
	return piface.UnmarshalOutput{}, errors.New("%T does not implement Marshal", v)
	}
	return piface.UnmarshalOutput{}, unmarshaler.Unmarshal(in.Buf)
	}

	func legacyMerge(in piface.MergeInput) piface.MergeOutput {
	dstv := in.Destination.(unwrapper).protoUnwrap()
	merger, ok := dstv.(legacyMerger)
	if !ok {
	return piface.MergeOutput{}
	}
	merger.Merge(Export{}.ProtoMessageV1Of(in.Source))
	return piface.MergeOutput{Flags: piface.MergeComplete}
	}

	// aberrantMessageType implements MessageType for all types other than pointer-to-struct.
	type aberrantMessageType struct {
	t reflect.Type
	}

	func (mt aberrantMessageType) New() pref.Message {
	return aberrantMessage{reflect.Zero(mt.t)}
	}
	func (mt aberrantMessageType) Zero() pref.Message {
	return aberrantMessage{reflect.Zero(mt.t)}
	}
	func (mt aberrantMessageType) GoType() reflect.Type {
	return mt.t
	}
	func (mt aberrantMessageType) Descriptor() pref.MessageDescriptor {
	return LegacyLoadMessageDesc(mt.t)
	}

	// aberrantMessage implements Message for all types other than pointer-to-struct.
	//
	// When the underlying type implements legacyMarshaler or legacyUnmarshaler,
	// the aberrant Message can be marshaled or unmarshaled. Otherwise, there is
	// not much that can be done with values of this type.
	type aberrantMessage struct {
	v reflect.Value
	}

	func (m aberrantMessage) ProtoReflect() pref.Message {
	return m
	}

	func (m aberrantMessage) Descriptor() pref.MessageDescriptor {
	return LegacyLoadMessageDesc(m.v.Type())
	}
	func (m aberrantMessage) Type() pref.MessageType {
	return aberrantMessageType{m.v.Type()}
	}
	func (m aberrantMessage) New() pref.Message {
	return aberrantMessage{reflect.Zero(m.v.Type())}
	}
	func (m aberrantMessage) Interface() pref.ProtoMessage {
	return m
	}
	func (m aberrantMessage) Range(f func(pref.FieldDescriptor, pref.Value) bool) {
	}
	func (m aberrantMessage) Has(pref.FieldDescriptor) bool {
	panic("invalid field descriptor")
	}
	func (m aberrantMessage) Clear(pref.FieldDescriptor) {
	panic("invalid field descriptor")
	}
	func (m aberrantMessage) Get(pref.FieldDescriptor) pref.Value {
	panic("invalid field descriptor")
	}
	func (m aberrantMessage) Set(pref.FieldDescriptor, pref.Value) {
	panic("invalid field descriptor")
	}
	func (m aberrantMessage) Mutable(pref.FieldDescriptor) pref.Value {
	panic("invalid field descriptor")
	}
	func (m aberrantMessage) NewField(pref.FieldDescriptor) pref.Value {
	panic("invalid field descriptor")
	}
	func (m aberrantMessage) WhichOneof(pref.OneofDescriptor) pref.FieldDescriptor {
	panic("invalid oneof descriptor")
	}
	func (m aberrantMessage) GetUnknown() pref.RawFields {
	return nil
	}
	func (m aberrantMessage) SetUnknown(pref.RawFields) {
	// SetUnknown discards its input on messages which don't support unknown field storage.
	}
	func (m aberrantMessage) IsValid() bool {
	// An invalid message is a read-only, empty message. Since we don't know anything
	// about the alleged contents of this message, we can't say with confidence that
	// it is invalid in this sense. Therefore, report it as valid.
	return true
	}
	func (m aberrantMessage) ProtoMethods() *piface.Methods {
	return aberrantProtoMethods
	}
	func (m aberrantMessage) protoUnwrap() interface{} {
	return m.v.Interface()
	}