internal/filedesc, internal/filetype: initial commit

The internal/fileinit package is split apart into two packages:
* internal/filedesc constructs descriptors from the raw proto.
It is very similar to the previous internal/fileinit package.
* internal/filetype wraps descriptors with Go type information

Overview:
* The internal/fileinit package will be deleted in a future CL.
It is kept around since the v1 repo currently depends on it.
* The internal/prototype package is deleted. All former usages of it
are now using internal/filedesc instead. Most significantly,
the reflect/protodesc package was almost entirely re-written.
* The internal/impl package drops support for messages that do not
have a Descriptor method (pre-2016). This removes a significant amount
of technical debt.
filedesc.Builder to parse raw descriptors.
* The internal/encoding/defval package now handles enum values by name.

Change-Id: I3957bcc8588a70470fd6c7de1122216b80615ab7
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/182360
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/legacy_enum.go b/internal/impl/legacy_enum.go
index 6758e74..7cd05bf 100644
--- a/internal/impl/legacy_enum.go
+++ b/internal/impl/legacy_enum.go
@@ -6,12 +6,11 @@
 
 import (
 	"fmt"
-	"math"
 	"reflect"
 	"sync"
 
-	ptype "google.golang.org/protobuf/internal/prototype"
 	pvalue "google.golang.org/protobuf/internal/value"
+	"google.golang.org/protobuf/reflect/protoreflect"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/reflect/prototype"
 )
@@ -94,78 +93,29 @@
 		return ed.(pref.EnumDescriptor)
 	}
 
-	// Slow-path: initialize EnumDescriptor from the proto descriptor.
-	if t.Kind() != reflect.Int32 || t.PkgPath() == "" {
-		panic(fmt.Sprintf("got %v, want named int32 kind", t))
-	}
-	if t == legacyEnumNumberType {
-		panic(fmt.Sprintf("cannot be %v", t))
-	}
-
-	// Derive the enum descriptor from the raw descriptor proto.
-	e := new(ptype.StandaloneEnum)
+	// Slow-path: initialize EnumDescriptor from the raw descriptor.
 	ev := reflect.Zero(t).Interface()
 	if _, ok := ev.(pref.Enum); ok {
 		panic(fmt.Sprintf("%v already implements proto.Enum", t))
 	}
-	if ed, ok := ev.(enumV1); ok {
-		b, idxs := ed.EnumDescriptor()
-		fd := legacyLoadFileDesc(b)
-
-		// Derive syntax.
-		switch fd.GetSyntax() {
-		case "proto2", "":
-			e.Syntax = pref.Proto2
-		case "proto3":
-			e.Syntax = pref.Proto3
-		}
-
-		// Derive the full name and correct enum descriptor.
-		var ed *legacyEnumDescriptorProto
-		e.FullName = pref.FullName(fd.GetPackage())
-		if len(idxs) == 1 {
-			ed = fd.EnumType[idxs[0]]
-			e.FullName = e.FullName.Append(pref.Name(ed.GetName()))
-		} else {
-			md := fd.MessageType[idxs[0]]
-			e.FullName = e.FullName.Append(pref.Name(md.GetName()))
-			for _, i := range idxs[1 : len(idxs)-1] {
-				md = md.NestedType[i]
-				e.FullName = e.FullName.Append(pref.Name(md.GetName()))
-			}
-			ed = md.EnumType[idxs[len(idxs)-1]]
-			e.FullName = e.FullName.Append(pref.Name(ed.GetName()))
-		}
-
-		// Derive the enum values.
-		for _, vd := range ed.Value {
-			e.Values = append(e.Values, ptype.EnumValue{
-				Name:   pref.Name(vd.GetName()),
-				Number: pref.EnumNumber(vd.GetNumber()),
-			})
-		}
-	} else {
-		// If the type does not implement enumV1, then there is no reliable
-		// way to derive the original protobuf type information.
-		// We are unable to use the global enum registry since it is
-		// unfortunately keyed by the full name, which we do not know.
-		// Furthermore, some generated enums register with a fork of
-		// golang/protobuf so the enum may not even be found in the registry.
-		//
-		// Instead, create a bogus enum descriptor to ensure that
-		// most operations continue to work. For example, prototext and protojson
-		// will be unable to parse a message with an enum value by name.
-		e.Syntax = pref.Proto2
-		e.FullName = legacyDeriveFullName(t)
-		e.Values = []ptype.EnumValue{{Name: "INVALID", Number: math.MinInt32}}
+	edV1, ok := ev.(enumV1)
+	if !ok {
+		panic(fmt.Sprintf("enum %v is no longer supported; please regenerate", t))
 	}
+	b, idxs := edV1.EnumDescriptor()
 
-	ed, err := ptype.NewEnum(e)
-	if err != nil {
-		panic(err)
+	var ed pref.EnumDescriptor
+	if len(idxs) == 1 {
+		ed = legacyLoadFileDesc(b).Enums().Get(idxs[0])
+	} else {
+		md := legacyLoadFileDesc(b).Messages().Get(idxs[0])
+		for _, i := range idxs[1 : len(idxs)-1] {
+			md = md.Messages().Get(i)
+		}
+		ed = md.Enums().Get(idxs[len(idxs)-1])
 	}
 	if ed, ok := legacyEnumDescCache.LoadOrStore(t, ed); ok {
-		return ed.(pref.EnumDescriptor)
+		return ed.(protoreflect.EnumDescriptor)
 	}
 	return ed
 }
diff --git a/internal/impl/legacy_extension.go b/internal/impl/legacy_extension.go
index 33ca82c..ca3475f 100644
--- a/internal/impl/legacy_extension.go
+++ b/internal/impl/legacy_extension.go
@@ -11,7 +11,7 @@
 
 	"google.golang.org/protobuf/internal/descfmt"
 	ptag "google.golang.org/protobuf/internal/encoding/tag"
-	ptype "google.golang.org/protobuf/internal/prototype"
+	"google.golang.org/protobuf/internal/filedesc"
 	pvalue "google.golang.org/protobuf/internal/value"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 	preg "google.golang.org/protobuf/reflect/protoregistry"
@@ -112,7 +112,7 @@
 		}
 		if ed, ok := reflect.Zero(t).Interface().(enumV1); ok && protoPkg == "" {
 			b, _ := ed.EnumDescriptor()
-			protoPkg = legacyLoadFileDesc(b).GetPackage()
+			protoPkg = string(legacyLoadFileDesc(b).Package())
 		}
 
 		if protoPkg != "" {
@@ -159,46 +159,45 @@
 		return t.(pref.ExtensionType)
 	}
 
-	// Derive basic field information from the struct tag.
+	// Resolve enum or message dependencies.
+	var ed pref.EnumDescriptor
+	var md pref.MessageDescriptor
 	t := reflect.TypeOf(d.ExtensionType)
 	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()
 	}
-	f := ptag.Unmarshal(d.Tag, t)
+	switch v := reflect.Zero(t).Interface().(type) {
+	case pref.Enum:
+		ed = v.Descriptor()
+	case enumV1:
+		ed = LegacyLoadEnumDesc(t)
+	case pref.ProtoMessage:
+		md = v.ProtoReflect().Descriptor()
+	case messageV1:
+		md = LegacyLoadMessageDesc(t)
+	}
+
+	// Derive basic field information from the struct tag.
+	var evs pref.EnumValueDescriptors
+	if ed != nil {
+		evs = ed.Values()
+	}
+	fd := ptag.Unmarshal(d.Tag, t, evs).(*filedesc.Field)
 
 	// Construct a v2 ExtensionType.
-	var ed pref.EnumDescriptor
-	var md pref.MessageDescriptor
-	switch f.Kind {
-	case pref.EnumKind:
-		if e, ok := reflect.Zero(t).Interface().(pref.Enum); ok {
-			ed = e.Descriptor()
-		} else {
-			ed = LegacyLoadEnumDesc(t)
-		}
-	case pref.MessageKind, pref.GroupKind:
-		if m, ok := reflect.Zero(t).Interface().(pref.ProtoMessage); ok {
-			md = m.ProtoReflect().Descriptor()
-		} else {
-			md = LegacyLoadMessageDesc(t)
-		}
-	}
-	xd, err := ptype.NewExtension(&ptype.StandaloneExtension{
-		FullName:     pref.FullName(d.Name),
-		Number:       pref.FieldNumber(d.Field),
-		Cardinality:  f.Cardinality,
-		Kind:         f.Kind,
-		Default:      f.Default,
-		Options:      f.Options,
-		EnumType:     ed,
-		MessageType:  md,
-		ExtendedType: Export{}.MessageDescriptorOf(d.ExtendedType),
-	})
-	if err != nil {
-		panic(err)
-	}
+	xd := &filedesc.Extension{L2: new(filedesc.ExtensionL2)}
+	xd.L0.ParentFile = filedesc.SurrogateProto2
+	xd.L0.FullName = pref.FullName(d.Name)
+	xd.L1.Number = pref.FieldNumber(d.Field)
+	xd.L2.Cardinality = fd.L1.Cardinality
+	xd.L1.Kind = fd.L1.Kind
+	xd.L2.IsPacked = fd.L1.IsPacked
+	xd.L2.Default = fd.L1.Default
+	xd.L1.Extendee = Export{}.MessageDescriptorOf(d.ExtendedType)
+	xd.L2.Enum = ed
+	xd.L2.Message = md
 	xt := LegacyExtensionTypeOf(xd, t)
 
 	// Cache the conversion for both directions.
diff --git a/internal/impl/legacy_extension_test.go b/internal/impl/legacy_extension_test.go
deleted file mode 100644
index 6ccfa40..0000000
--- a/internal/impl/legacy_extension_test.go
+++ /dev/null
@@ -1,75 +0,0 @@
-// 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_test
-
-import (
-	"reflect"
-	"testing"
-
-	pimpl "google.golang.org/protobuf/internal/impl"
-	ptype "google.golang.org/protobuf/internal/prototype"
-	pref "google.golang.org/protobuf/reflect/protoreflect"
-	piface "google.golang.org/protobuf/runtime/protoiface"
-
-	proto2_20180125 "google.golang.org/protobuf/internal/testprotos/legacy/proto2.v1.0.0-20180125-92554152"
-)
-
-type legacyExtendedMessage struct {
-	XXX_unrecognized       []byte
-	XXX_InternalExtensions map[int32]pimpl.ExtensionField
-}
-
-func (*legacyExtendedMessage) Reset()         {}
-func (*legacyExtendedMessage) String() string { return "" }
-func (*legacyExtendedMessage) ProtoMessage()  {}
-func (*legacyExtendedMessage) ExtensionRangeArray() []piface.ExtensionRangeV1 {
-	return []piface.ExtensionRangeV1{{Start: 10000, End: 20000}}
-}
-
-func mustMakeExtensionType(x *ptype.StandaloneExtension, v interface{}) pref.ExtensionType {
-	xd, err := ptype.NewExtension(x)
-	if err != nil {
-		panic(err)
-	}
-	return pimpl.LegacyExtensionTypeOf(xd, reflect.TypeOf(v))
-}
-
-var (
-	extParentDesc    = pimpl.Export{}.MessageDescriptorOf((*legacyExtendedMessage)(nil))
-	extMessageV1Desc = pimpl.Export{}.MessageDescriptorOf((*proto2_20180125.Message_ChildMessage)(nil))
-
-	wantType = mustMakeExtensionType(&ptype.StandaloneExtension{
-		FullName:     "fizz.buzz.optional_message_v1",
-		Number:       10007,
-		Cardinality:  pref.Optional,
-		Kind:         pref.MessageKind,
-		MessageType:  extMessageV1Desc,
-		ExtendedType: extParentDesc,
-	}, (*proto2_20180125.Message_ChildMessage)(nil))
-	wantDesc = &piface.ExtensionDescV1{
-		ExtendedType:  (*legacyExtendedMessage)(nil),
-		ExtensionType: (*proto2_20180125.Message_ChildMessage)(nil),
-		Field:         10007,
-		Name:          "fizz.buzz.optional_message_v1",
-		Tag:           "bytes,10007,opt,name=optional_message_v1",
-	}
-)
-
-func BenchmarkConvert(b *testing.B) {
-	b.ReportAllocs()
-	for i := 0; i < b.N; i++ {
-		xd := pimpl.Export{}.ExtensionDescFromType(wantType)
-		gotType := pimpl.Export{}.ExtensionTypeFromDesc(xd)
-		if gotType != wantType {
-			b.Fatalf("ExtensionType mismatch: got %p, want %p", gotType, wantType)
-		}
-
-		xt := pimpl.Export{}.ExtensionTypeFromDesc(wantDesc)
-		gotDesc := pimpl.Export{}.ExtensionDescFromType(xt)
-		if gotDesc != wantDesc {
-			b.Fatalf("ExtensionDesc mismatch: got %p, want %p", gotDesc, wantDesc)
-		}
-	}
-}
diff --git a/internal/impl/legacy_file.go b/internal/impl/legacy_file.go
index ddf33f7..b1293c6 100644
--- a/internal/impl/legacy_file.go
+++ b/internal/impl/legacy_file.go
@@ -9,6 +9,10 @@
 	"compress/gzip"
 	"io/ioutil"
 	"sync"
+
+	"google.golang.org/protobuf/internal/filedesc"
+	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/reflect/protoregistry"
 )
 
 // Every enum and message type generated by protoc-gen-go since commit 2fc053c5
@@ -28,7 +32,7 @@
 	}
 )
 
-var legacyFileDescCache sync.Map // map[*byte]*descriptorpb.FileDescriptorProto
+var legacyFileDescCache sync.Map // map[*byte]protoreflect.FileDescriptor
 
 // legacyLoadFileDesc unmarshals b as a compressed FileDescriptorProto message.
 //
@@ -36,10 +40,10 @@
 // concatenated series of GZIP files (which would require shenanigans that
 // rely on the concatenation properties of both protobufs and GZIP).
 // File descriptors generated by protoc-gen-go do not rely on that property.
-func legacyLoadFileDesc(b []byte) *legacyFileDescriptorProto {
+func legacyLoadFileDesc(b []byte) protoreflect.FileDescriptor {
 	// Fast-path: check whether we already have a cached file descriptor.
 	if fd, ok := legacyFileDescCache.Load(&b[0]); ok {
-		return fd.(*legacyFileDescriptorProto)
+		return fd.(protoreflect.FileDescriptor)
 	}
 
 	// Slow-path: decompress and unmarshal the file descriptor proto.
@@ -47,13 +51,23 @@
 	if err != nil {
 		panic(err)
 	}
-	b, err = ioutil.ReadAll(zr)
+	b2, err := ioutil.ReadAll(zr)
 	if err != nil {
 		panic(err)
 	}
-	fd := legacyParseFileDescProto(b)
+
+	fd := filedesc.DescBuilder{
+		RawDescriptor: b2,
+		FileRegistry:  resolverOnly{protoregistry.GlobalFiles}, // do not register back to global registry
+	}.Build().File
 	if fd, ok := legacyFileDescCache.LoadOrStore(&b[0], fd); ok {
-		return fd.(*legacyFileDescriptorProto)
+		return fd.(protoreflect.FileDescriptor)
 	}
 	return fd
 }
+
+type resolverOnly struct {
+	*protoregistry.Files
+}
+
+func (resolverOnly) Register(...protoreflect.FileDescriptor) error { return nil }
diff --git a/internal/impl/legacy_message.go b/internal/impl/legacy_message.go
index c54cfc1..58bb07c 100644
--- a/internal/impl/legacy_message.go
+++ b/internal/impl/legacy_message.go
@@ -7,12 +7,9 @@
 import (
 	"fmt"
 	"reflect"
-	"strings"
 	"sync"
-	"unicode"
 
-	ptag "google.golang.org/protobuf/internal/encoding/tag"
-	ptype "google.golang.org/protobuf/internal/prototype"
+	"google.golang.org/protobuf/reflect/protoreflect"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/reflect/prototype"
 )
@@ -50,276 +47,35 @@
 	return mt
 }
 
-var (
-	legacyMessageDescLock  sync.Mutex
-	legacyMessageDescCache sync.Map // map[reflect.Type]protoreflect.MessageDescriptor
-)
+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 legacyMessageDescSet{}.Load(t)
-}
-
-type legacyMessageDescSet struct {
-	visited map[reflect.Type]*ptype.StandaloneMessage
-	descs   []*ptype.StandaloneMessage
-	types   []reflect.Type
-}
-
-func (ms legacyMessageDescSet) Load(t reflect.Type) 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 Go type.
-	//
-	// Hold a global lock during message creation to ensure that each Go type
-	// maps to exactly one MessageDescriptor. After obtaining the lock, we must
-	// check again whether the message has already been handled.
-	legacyMessageDescLock.Lock()
-	defer legacyMessageDescLock.Unlock()
-	if mi, ok := legacyMessageDescCache.Load(t); ok {
-		return mi.(pref.MessageDescriptor)
-	}
-
-	// Processing t recursively populates descs and types with all sub-messages.
-	// The descriptor for the first type is guaranteed to be at the front.
-	ms.processMessage(t)
-
-	// Within a proto file it is possible for cyclic dependencies to exist
-	// between multiple message types. When these cases arise, the set of
-	// message descriptors must be created together.
-	mds, err := ptype.NewMessages(ms.descs)
-	if err != nil {
-		panic(err)
-	}
-	for i, md := range mds {
-		// Protobuf semantics represents map entries under-the-hood as
-		// pseudo-messages (has a descriptor, but no generated Go type).
-		// Avoid caching these fake messages.
-		if t := ms.types[i]; t.Kind() != reflect.Map {
-			legacyMessageDescCache.Store(t, md)
-		}
-	}
-	return mds[0]
-}
-
-func (ms *legacyMessageDescSet) processMessage(t reflect.Type) pref.MessageDescriptor {
-	// Fast-path: Obtain a placeholder if the message is already processed.
-	if m, ok := ms.visited[t]; ok {
-		return ptype.PlaceholderMessage(m.FullName)
-	}
-
-	// Slow-path: Walk over the struct fields to derive the message descriptor.
-	if t.Kind() != reflect.Ptr || t.Elem().Kind() != reflect.Struct || t.Elem().PkgPath() == "" {
-		panic(fmt.Sprintf("got %v, want named *struct kind", t))
-	}
-
-	// Derive name and syntax from the raw descriptor.
-	m := new(ptype.StandaloneMessage)
+	// Slow-path: initialize MessageDescriptor from the raw descriptor.
 	mv := reflect.New(t.Elem()).Interface()
 	if _, ok := mv.(pref.ProtoMessage); ok {
 		panic(fmt.Sprintf("%v already implements proto.Message", t))
 	}
-	if md, ok := mv.(messageV1); ok {
-		b, idxs := md.Descriptor()
-		fd := legacyLoadFileDesc(b)
+	mdV1, ok := mv.(messageV1)
+	if !ok {
+		panic(fmt.Sprintf("message %v is no longer supported; please regenerate", t))
+	}
+	b, idxs := mdV1.Descriptor()
 
-		// Derive syntax.
-		switch fd.GetSyntax() {
-		case "proto2", "":
-			m.Syntax = pref.Proto2
-		case "proto3":
-			m.Syntax = pref.Proto3
-		}
-
-		// Derive full name.
-		md := fd.MessageType[idxs[0]]
-		m.FullName = pref.FullName(fd.GetPackage()).Append(pref.Name(md.GetName()))
-		for _, i := range idxs[1:] {
-			md = md.NestedType[i]
-			m.FullName = m.FullName.Append(pref.Name(md.GetName()))
-		}
-	} else {
-		// If the type does not implement messageV1, then the only way to
-		// obtain the full name is through the registry. However, this is
-		// unreliable as some generated messages register with a fork of
-		// golang/protobuf, so the registry may not have this information.
-		m.FullName = legacyDeriveFullName(t.Elem())
-		m.Syntax = pref.Proto2
-
-		// 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:
-					m.Syntax = pref.Proto3
-				}
-				for _, s := range strings.Split(tag, ",") {
-					if s == "proto3" {
-						m.Syntax = pref.Proto3
-					}
-				}
-			}
-		}
+	md := legacyLoadFileDesc(b).Messages().Get(idxs[0])
+	for _, i := range idxs[1:] {
+		md = md.Messages().Get(i)
 	}
-	ms.visit(m, t)
-
-	// Obtain a list of oneof wrapper types.
-	var oneofWrappers []reflect.Type
-	if fn, ok := t.MethodByName("XXX_OneofFuncs"); ok {
-		vs := fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))})[3]
-		for _, v := range vs.Interface().([]interface{}) {
-			oneofWrappers = append(oneofWrappers, reflect.TypeOf(v))
-		}
+	if md, ok := legacyMessageDescCache.LoadOrStore(t, md); ok {
+		return md.(protoreflect.MessageDescriptor)
 	}
-	if fn, ok := t.MethodByName("XXX_OneofWrappers"); ok {
-		vs := fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))})[0]
-		for _, v := range vs.Interface().([]interface{}) {
-			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)
-			m.ExtensionRanges = append(m.ExtensionRanges, [2]pref.FieldNumber{
-				pref.FieldNumber(v.FieldByName("Start").Int()),
-				pref.FieldNumber(v.FieldByName("End").Int() + 1),
-			})
-		}
-	}
-
-	// 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")
-			m.Fields = append(m.Fields, ms.parseField(tag, tagKey, tagVal, f.Type, m))
-		}
-		if tag := f.Tag.Get("protobuf_oneof"); tag != "" {
-			name := pref.Name(tag)
-			m.Oneofs = append(m.Oneofs, ptype.Oneof{Name: name})
-			for _, t := range oneofWrappers {
-				if t.Implements(f.Type) {
-					f := t.Elem().Field(0)
-					if tag := f.Tag.Get("protobuf"); tag != "" {
-						ft := ms.parseField(tag, "", "", f.Type, m)
-						ft.OneofName = name
-						m.Fields = append(m.Fields, ft)
-					}
-				}
-			}
-		}
-	}
-
-	return ptype.PlaceholderMessage(m.FullName)
-}
-
-func (ms *legacyMessageDescSet) parseField(tag, tagKey, tagVal string, goType reflect.Type, parent *ptype.StandaloneMessage) ptype.Field {
-	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()
-	}
-	f := ptag.Unmarshal(tag, t)
-
-	// Populate EnumType and MessageType.
-	if f.EnumType == nil && f.Kind == pref.EnumKind {
-		if ev, ok := reflect.Zero(t).Interface().(pref.Enum); ok {
-			f.EnumType = ev.Descriptor()
-		} else {
-			f.EnumType = LegacyLoadEnumDesc(t)
-		}
-	}
-	if f.MessageType == nil && (f.Kind == pref.MessageKind || f.Kind == pref.GroupKind) {
-		if mv, ok := reflect.Zero(t).Interface().(pref.ProtoMessage); ok {
-			f.MessageType = mv.ProtoReflect().Descriptor()
-		} else if t.Kind() == reflect.Map {
-			m := &ptype.StandaloneMessage{
-				Syntax:     parent.Syntax,
-				FullName:   parent.FullName.Append(legacyMapEntryName(f.Name)),
-				IsMapEntry: true,
-				Fields: []ptype.Field{
-					ms.parseField(tagKey, "", "", t.Key(), nil),
-					ms.parseField(tagVal, "", "", t.Elem(), nil),
-				},
-			}
-			ms.visit(m, t)
-			f.MessageType = ptype.PlaceholderMessage(m.FullName)
-		} else if mv, ok := legacyMessageDescCache.Load(t); ok {
-			f.MessageType = mv.(pref.MessageDescriptor)
-		} else {
-			f.MessageType = ms.processMessage(t)
-		}
-	}
-	return f
-}
-
-func (ms *legacyMessageDescSet) visit(m *ptype.StandaloneMessage, t reflect.Type) {
-	if ms.visited == nil {
-		ms.visited = make(map[reflect.Type]*ptype.StandaloneMessage)
-	}
-	if t.Kind() != reflect.Map {
-		ms.visited[t] = m
-	}
-	ms.descs = append(ms.descs, m)
-	ms.types = append(ms.types, t)
-}
-
-// legacyDeriveFullName derives a fully qualified protobuf name for the given Go type
-// The provided name is not guaranteed to be stable nor universally unique.
-// It should be sufficiently unique within a program.
-func legacyDeriveFullName(t reflect.Type) pref.FullName {
-	sanitize := func(r rune) rune {
-		switch {
-		case r == '/':
-			return '.'
-		case 'a' <= r && r <= 'z', 'A' <= r && r <= 'Z', '0' <= r && r <= '9':
-			return r
-		default:
-			return '_'
-		}
-	}
-	prefix := strings.Map(sanitize, t.PkgPath())
-	suffix := strings.Map(sanitize, t.Name())
-	if suffix == "" {
-		suffix = fmt.Sprintf("UnknownX%X", reflect.ValueOf(t).Pointer())
-	}
-
-	ss := append(strings.Split(prefix, "."), suffix)
-	for i, s := range ss {
-		if s == "" || ('0' <= s[0] && s[0] <= '9') {
-			ss[i] = "x" + s
-		}
-	}
-	return pref.FullName(strings.Join(ss, "."))
-}
-
-// legacyMapEntryName derives the message name for a map field of a given name.
-// This is identical to MapEntryName from parser.cc in the protoc source.
-func legacyMapEntryName(s pref.Name) pref.Name {
-	var b []byte
-	nextUpper := true
-	for i := 0; i < len(s); i++ {
-		if c := s[i]; c == '_' {
-			nextUpper = true
-		} else {
-			if nextUpper {
-				c = byte(unicode.ToUpper(rune(c)))
-				nextUpper = false
-			}
-			b = append(b, c)
-		}
-	}
-	return pref.Name(append(b, "Entry"...))
+	return md
 }
diff --git a/internal/impl/legacy_parse.go b/internal/impl/legacy_parse.go
deleted file mode 100644
index 90ba1b7..0000000
--- a/internal/impl/legacy_parse.go
+++ /dev/null
@@ -1,169 +0,0 @@
-// Copyright 2019 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 (
-	"google.golang.org/protobuf/internal/encoding/wire"
-	"google.golang.org/protobuf/internal/fieldnum"
-)
-
-// To avoid a dependency from legacy to descriptor.proto, use a hand-written parser
-// for the bits of the descriptor we need.
-//
-// TODO: Consider unifying this with the parser in fileinit.
-
-type legacyFileDescriptorProto struct {
-	Syntax      string
-	Package     string
-	EnumType    []*legacyEnumDescriptorProto
-	MessageType []*legacyDescriptorProto
-}
-
-func (fd legacyFileDescriptorProto) GetSyntax() string  { return fd.Syntax }
-func (fd legacyFileDescriptorProto) GetPackage() string { return fd.Package }
-
-func legacyParseFileDescProto(b []byte) *legacyFileDescriptorProto {
-	fd := &legacyFileDescriptorProto{}
-	for len(b) > 0 {
-		num, typ, n := wire.ConsumeTag(b)
-		legacyParseCheck(n)
-		b = b[n:]
-		switch typ {
-		case wire.BytesType:
-			v, n := wire.ConsumeBytes(b)
-			b = b[n:]
-			switch num {
-			case fieldnum.FileDescriptorProto_Syntax:
-				fd.Syntax = string(v)
-			case fieldnum.FileDescriptorProto_Package:
-				fd.Package = string(v)
-			case fieldnum.FileDescriptorProto_EnumType:
-				fd.EnumType = append(fd.EnumType, legacyParseEnumDescProto(v))
-			case fieldnum.FileDescriptorProto_MessageType:
-				fd.MessageType = append(fd.MessageType, parseDescProto(v))
-			}
-		default:
-			n := wire.ConsumeFieldValue(num, typ, b)
-			legacyParseCheck(n)
-			b = b[n:]
-		}
-	}
-	return fd
-}
-
-type legacyDescriptorProto struct {
-	Name       string
-	NestedType []*legacyDescriptorProto
-	EnumType   []*legacyEnumDescriptorProto
-}
-
-func (md legacyDescriptorProto) GetName() string { return md.Name }
-
-func parseDescProto(b []byte) *legacyDescriptorProto {
-	md := &legacyDescriptorProto{}
-	for len(b) > 0 {
-		num, typ, n := wire.ConsumeTag(b)
-		legacyParseCheck(n)
-		b = b[n:]
-		switch typ {
-		case wire.BytesType:
-			v, n := wire.ConsumeBytes(b)
-			legacyParseCheck(n)
-			b = b[n:]
-			switch num {
-			case fieldnum.DescriptorProto_Name:
-				md.Name = string(v)
-			case fieldnum.DescriptorProto_NestedType:
-				md.NestedType = append(md.NestedType, parseDescProto(v))
-			case fieldnum.DescriptorProto_EnumType:
-				md.EnumType = append(md.EnumType, legacyParseEnumDescProto(v))
-			}
-		default:
-			n := wire.ConsumeFieldValue(num, typ, b)
-			legacyParseCheck(n)
-			b = b[n:]
-		}
-	}
-	return md
-}
-
-type legacyEnumDescriptorProto struct {
-	Name  string
-	Value []*legacyEnumValueDescriptorProto
-}
-
-func (ed legacyEnumDescriptorProto) GetName() string { return ed.Name }
-
-func legacyParseEnumDescProto(b []byte) *legacyEnumDescriptorProto {
-	ed := &legacyEnumDescriptorProto{}
-	for len(b) > 0 {
-		num, typ, n := wire.ConsumeTag(b)
-		legacyParseCheck(n)
-		b = b[n:]
-		switch typ {
-		case wire.BytesType:
-			v, n := wire.ConsumeBytes(b)
-			legacyParseCheck(n)
-			b = b[n:]
-			switch num {
-			case fieldnum.EnumDescriptorProto_Name:
-				ed.Name = string(v)
-			case fieldnum.EnumDescriptorProto_Value:
-				ed.Value = append(ed.Value, legacyParseEnumValueDescProto(v))
-			}
-		default:
-			n := wire.ConsumeFieldValue(num, typ, b)
-			legacyParseCheck(n)
-			b = b[n:]
-		}
-	}
-	return ed
-}
-
-type legacyEnumValueDescriptorProto struct {
-	Name   string
-	Number int32
-}
-
-func (ed legacyEnumValueDescriptorProto) GetName() string  { return ed.Name }
-func (ed legacyEnumValueDescriptorProto) GetNumber() int32 { return ed.Number }
-
-func legacyParseEnumValueDescProto(b []byte) *legacyEnumValueDescriptorProto {
-	vd := &legacyEnumValueDescriptorProto{}
-	for len(b) > 0 {
-		num, typ, n := wire.ConsumeTag(b)
-		legacyParseCheck(n)
-		b = b[n:]
-		switch typ {
-		case wire.VarintType:
-			v, n := wire.ConsumeVarint(b)
-			legacyParseCheck(n)
-			b = b[n:]
-			switch num {
-			case fieldnum.EnumValueDescriptorProto_Number:
-				vd.Number = int32(v)
-			}
-		case wire.BytesType:
-			v, n := wire.ConsumeBytes(b)
-			legacyParseCheck(n)
-			b = b[n:]
-			switch num {
-			case fieldnum.EnumDescriptorProto_Name:
-				vd.Name = string(v)
-			}
-		default:
-			n := wire.ConsumeFieldValue(num, typ, b)
-			legacyParseCheck(n)
-			b = b[n:]
-		}
-	}
-	return vd
-}
-
-func legacyParseCheck(n int) {
-	if n < 0 {
-		panic(wire.ParseError(n))
-	}
-}
diff --git a/internal/impl/legacy_test.go b/internal/impl/legacy_test.go
index fc29cdb..a51ae03 100644
--- a/internal/impl/legacy_test.go
+++ b/internal/impl/legacy_test.go
@@ -5,326 +5,333 @@
 package impl_test
 
 import (
+	"fmt"
 	"reflect"
 	"sync"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-cmp/cmp/cmpopts"
+	"google.golang.org/protobuf/encoding/prototext"
 	pimpl "google.golang.org/protobuf/internal/impl"
-	pragma "google.golang.org/protobuf/internal/pragma"
-	ptype "google.golang.org/protobuf/internal/prototype"
+	"google.golang.org/protobuf/internal/pragma"
 	"google.golang.org/protobuf/internal/scalar"
+	"google.golang.org/protobuf/proto"
+	pdesc "google.golang.org/protobuf/reflect/protodesc"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 	preg "google.golang.org/protobuf/reflect/protoregistry"
 	piface "google.golang.org/protobuf/runtime/protoiface"
 
 	proto2_20180125 "google.golang.org/protobuf/internal/testprotos/legacy/proto2.v1.0.0-20180125-92554152"
+	"google.golang.org/protobuf/types/descriptorpb"
 )
 
-type legacyTestMessage struct {
+type LegacyTestMessage struct {
 	XXX_unrecognized       []byte
 	XXX_InternalExtensions map[int32]pimpl.ExtensionField
 }
 
-func (*legacyTestMessage) Reset()         {}
-func (*legacyTestMessage) String() string { return "" }
-func (*legacyTestMessage) ProtoMessage()  {}
-func (*legacyTestMessage) ExtensionRangeArray() []piface.ExtensionRangeV1 {
+func (*LegacyTestMessage) Reset()         {}
+func (*LegacyTestMessage) String() string { return "" }
+func (*LegacyTestMessage) ProtoMessage()  {}
+func (*LegacyTestMessage) ExtensionRangeArray() []piface.ExtensionRangeV1 {
 	return []piface.ExtensionRangeV1{{Start: 10, End: 20}, {Start: 40, End: 80}, {Start: 10000, End: 20000}}
 }
+func (*LegacyTestMessage) Descriptor() ([]byte, []int) { return legacyFD, []int{0} }
+
+var legacyFD = func() []byte {
+	b, _ := proto.Marshal(pdesc.ToFileDescriptorProto(mustMakeFileDesc(`
+		name:   "legacy.proto"
+		syntax: "proto2"
+		message_type: [{
+			name:            "LegacyTestMessage"
+			extension_range: [{start:10 end:20}, {start:40 end:80}, {start:10000 end:20000}]
+		}]
+	`, nil)))
+	return pimpl.Export{}.CompressGZIP(b)
+}()
 
 func init() {
-	mt := pimpl.Export{}.MessageTypeOf(&legacyTestMessage{})
+	mt := pimpl.Export{}.MessageTypeOf((*LegacyTestMessage)(nil))
+	preg.GlobalFiles.Register(mt.ParentFile())
 	preg.GlobalTypes.Register(mt)
 }
 
+func mustMakeExtensionType(fileDesc, extDesc string, t interface{}, r pdesc.Resolver) pref.ExtensionType {
+	s := fmt.Sprintf(`name:"test.proto" syntax:"proto2" %s extension:[{%s}]`, fileDesc, extDesc)
+	xd := mustMakeFileDesc(s, r).Extensions().Get(0)
+	return pimpl.LegacyExtensionTypeOf(xd, reflect.TypeOf(t))
+}
+
+func mustMakeFileDesc(s string, r pdesc.Resolver) pref.FileDescriptor {
+	pb := new(descriptorpb.FileDescriptorProto)
+	if err := prototext.Unmarshal([]byte(s), pb); err != nil {
+		panic(err)
+	}
+	fd, err := pdesc.NewFile(pb, r)
+	if err != nil {
+		panic(err)
+	}
+	return fd
+}
+
 var (
-	testParentDesc    = pimpl.Export{}.MessageDescriptorOf((*legacyTestMessage)(nil))
+	testParentDesc    = pimpl.Export{}.MessageDescriptorOf((*LegacyTestMessage)(nil))
 	testEnumV1Desc    = pimpl.Export{}.EnumDescriptorOf(proto2_20180125.Message_ChildEnum(0))
 	testMessageV1Desc = pimpl.Export{}.MessageDescriptorOf((*proto2_20180125.Message_ChildMessage)(nil))
 	testEnumV2Desc    = enumProto2Type.Descriptor()
 	testMessageV2Desc = enumMessagesType.PBType.Descriptor()
 
+	depReg = preg.NewFiles(
+		testParentDesc.ParentFile(),
+		testEnumV1Desc.ParentFile(),
+		testMessageV1Desc.ParentFile(),
+		testEnumV2Desc.ParentFile(),
+		testMessageV2Desc.ParentFile(),
+	)
 	extensionTypes = []pref.ExtensionType{
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_bool",
-			Number:       10000,
-			Cardinality:  pref.Optional,
-			Kind:         pref.BoolKind,
-			Default:      pref.ValueOf(true),
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_int32",
-			Number:       10001,
-			Cardinality:  pref.Optional,
-			Kind:         pref.Int32Kind,
-			Default:      pref.ValueOf(int32(-12345)),
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_uint32",
-			Number:       10002,
-			Cardinality:  pref.Optional,
-			Kind:         pref.Uint32Kind,
-			Default:      pref.ValueOf(uint32(3200)),
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_float",
-			Number:       10003,
-			Cardinality:  pref.Optional,
-			Kind:         pref.FloatKind,
-			Default:      pref.ValueOf(float32(3.14159)),
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_string",
-			Number:       10004,
-			Cardinality:  pref.Optional,
-			Kind:         pref.StringKind,
-			Default:      pref.ValueOf(string("hello, \"world!\"\n")),
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_bytes",
-			Number:       10005,
-			Cardinality:  pref.Optional,
-			Kind:         pref.BytesKind,
-			Default:      pref.ValueOf([]byte("dead\xde\xad\xbe\xefbeef")),
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_enum_v1",
-			Number:       10006,
-			Cardinality:  pref.Optional,
-			Kind:         pref.EnumKind,
-			Default:      pref.ValueOf(pref.EnumNumber(0)),
-			EnumType:     testEnumV1Desc,
-			ExtendedType: testParentDesc,
-		}, proto2_20180125.Message_ChildEnum(0)),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_message_v1",
-			Number:       10007,
-			Cardinality:  pref.Optional,
-			Kind:         pref.MessageKind,
-			MessageType:  testMessageV1Desc,
-			ExtendedType: testParentDesc,
-		}, (*proto2_20180125.Message_ChildMessage)(nil)),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_enum_v2",
-			Number:       10008,
-			Cardinality:  pref.Optional,
-			Kind:         pref.EnumKind,
-			Default:      pref.ValueOf(pref.EnumNumber(57005)),
-			EnumType:     testEnumV2Desc,
-			ExtendedType: testParentDesc,
-		}, EnumProto2(0)),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.optional_message_v2",
-			Number:       10009,
-			Cardinality:  pref.Optional,
-			Kind:         pref.MessageKind,
-			MessageType:  testMessageV2Desc,
-			ExtendedType: testParentDesc,
-		}, (*EnumMessages)(nil)),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_bool",
-			Number:       10010,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.BoolKind,
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_int32",
-			Number:       10011,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.Int32Kind,
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_uint32",
-			Number:       10012,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.Uint32Kind,
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_float",
-			Number:       10013,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.FloatKind,
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_string",
-			Number:       10014,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.StringKind,
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_bytes",
-			Number:       10015,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.BytesKind,
-			ExtendedType: testParentDesc,
-		}, nil),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_enum_v1",
-			Number:       10016,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.EnumKind,
-			EnumType:     testEnumV1Desc,
-			ExtendedType: testParentDesc,
-		}, proto2_20180125.Message_ChildEnum(0)),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_message_v1",
-			Number:       10017,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.MessageKind,
-			MessageType:  testMessageV1Desc,
-			ExtendedType: testParentDesc,
-		}, (*proto2_20180125.Message_ChildMessage)(nil)),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_enum_v2",
-			Number:       10018,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.EnumKind,
-			EnumType:     testEnumV2Desc,
-			ExtendedType: testParentDesc,
-		}, EnumProto2(0)),
-		mustMakeExtensionType(&ptype.StandaloneExtension{
-			FullName:     "fizz.buzz.repeated_message_v2",
-			Number:       10019,
-			Cardinality:  pref.Repeated,
-			Kind:         pref.MessageKind,
-			MessageType:  testMessageV2Desc,
-			ExtendedType: testParentDesc,
-		}, (*EnumMessages)(nil)),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"optional_bool" number:10000 label:LABEL_OPTIONAL type:TYPE_BOOL default_value:"true" extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"optional_int32" number:10001 label:LABEL_OPTIONAL type:TYPE_INT32 default_value:"-12345" extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"optional_uint32" number:10002 label:LABEL_OPTIONAL type:TYPE_UINT32 default_value:"3200" extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"optional_float" number:10003 label:LABEL_OPTIONAL type:TYPE_FLOAT default_value:"3.14159" extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"optional_string" number:10004 label:LABEL_OPTIONAL type:TYPE_STRING default_value:"hello, \"world!\"\n" extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"optional_bytes" number:10005 label:LABEL_OPTIONAL type:TYPE_BYTES default_value:"dead\\336\\255\\276\\357beef" extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:["legacy.proto", "proto2.v1.0.0-20180125-92554152/test.proto"]`,
+			`name:"optional_enum_v1" number:10006 label:LABEL_OPTIONAL type:TYPE_ENUM type_name:".google.golang.org.proto2_20180125.Message.ChildEnum" default_value:"ALPHA" extendee:".LegacyTestMessage"`,
+			proto2_20180125.Message_ChildEnum(0), depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:["legacy.proto", "proto2.v1.0.0-20180125-92554152/test.proto"]`,
+			`name:"optional_message_v1" number:10007 label:LABEL_OPTIONAL type:TYPE_MESSAGE type_name:".google.golang.org.proto2_20180125.Message.ChildMessage" extendee:".LegacyTestMessage"`,
+			(*proto2_20180125.Message_ChildMessage)(nil), depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:["legacy.proto", "enum2.proto"]`,
+			`name:"optional_enum_v2" number:10008 label:LABEL_OPTIONAL type:TYPE_ENUM type_name:".EnumProto2" default_value:"DEAD" extendee:".LegacyTestMessage"`,
+			EnumProto2(0), depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:["legacy.proto", "enum-messages.proto"]`,
+			`name:"optional_message_v2" number:10009 label:LABEL_OPTIONAL type:TYPE_MESSAGE type_name:".EnumMessages" extendee:".LegacyTestMessage"`,
+			(*EnumMessages)(nil), depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"repeated_bool" number:10010 label:LABEL_REPEATED type:TYPE_BOOL extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"repeated_int32" number:10011 label:LABEL_REPEATED type:TYPE_INT32 extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"repeated_uint32" number:10012 label:LABEL_REPEATED type:TYPE_UINT32 extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"repeated_float" number:10013 label:LABEL_REPEATED type:TYPE_FLOAT extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"repeated_string" number:10014 label:LABEL_REPEATED type:TYPE_STRING extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:"legacy.proto"`,
+			`name:"repeated_bytes" number:10015 label:LABEL_REPEATED type:TYPE_BYTES extendee:".LegacyTestMessage"`,
+			nil, depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:["legacy.proto", "proto2.v1.0.0-20180125-92554152/test.proto"]`,
+			`name:"repeated_enum_v1" number:10016 label:LABEL_REPEATED type:TYPE_ENUM type_name:".google.golang.org.proto2_20180125.Message.ChildEnum" extendee:".LegacyTestMessage"`,
+			proto2_20180125.Message_ChildEnum(0), depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:["legacy.proto", "proto2.v1.0.0-20180125-92554152/test.proto"]`,
+			`name:"repeated_message_v1" number:10017 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".google.golang.org.proto2_20180125.Message.ChildMessage" extendee:".LegacyTestMessage"`,
+			(*proto2_20180125.Message_ChildMessage)(nil), depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:["legacy.proto", "enum2.proto"]`,
+			`name:"repeated_enum_v2" number:10018 label:LABEL_REPEATED type:TYPE_ENUM type_name:".EnumProto2" extendee:".LegacyTestMessage"`,
+			EnumProto2(0), depReg,
+		),
+		mustMakeExtensionType(
+			`package:"fizz.buzz" dependency:["legacy.proto", "enum-messages.proto"]`,
+			`name:"repeated_message_v2" number:10019 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".EnumMessages" extendee:".LegacyTestMessage"`,
+			(*EnumMessages)(nil), depReg,
+		),
 	}
 
 	extensionDescs = []*piface.ExtensionDescV1{{
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*bool)(nil),
 		Field:         10000,
 		Name:          "fizz.buzz.optional_bool",
 		Tag:           "varint,10000,opt,name=optional_bool,def=1",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*int32)(nil),
 		Field:         10001,
 		Name:          "fizz.buzz.optional_int32",
 		Tag:           "varint,10001,opt,name=optional_int32,def=-12345",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*uint32)(nil),
 		Field:         10002,
 		Name:          "fizz.buzz.optional_uint32",
 		Tag:           "varint,10002,opt,name=optional_uint32,def=3200",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*float32)(nil),
 		Field:         10003,
 		Name:          "fizz.buzz.optional_float",
 		Tag:           "fixed32,10003,opt,name=optional_float,def=3.14159",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*string)(nil),
 		Field:         10004,
 		Name:          "fizz.buzz.optional_string",
 		Tag:           "bytes,10004,opt,name=optional_string,def=hello, \"world!\"\n",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]byte)(nil),
 		Field:         10005,
 		Name:          "fizz.buzz.optional_bytes",
 		Tag:           "bytes,10005,opt,name=optional_bytes,def=dead\\336\\255\\276\\357beef",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*proto2_20180125.Message_ChildEnum)(nil),
 		Field:         10006,
 		Name:          "fizz.buzz.optional_enum_v1",
 		Tag:           "varint,10006,opt,name=optional_enum_v1,enum=google.golang.org.proto2_20180125.Message_ChildEnum,def=0",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*proto2_20180125.Message_ChildMessage)(nil),
 		Field:         10007,
 		Name:          "fizz.buzz.optional_message_v1",
 		Tag:           "bytes,10007,opt,name=optional_message_v1",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*EnumProto2)(nil),
 		Field:         10008,
 		Name:          "fizz.buzz.optional_enum_v2",
 		Tag:           "varint,10008,opt,name=optional_enum_v2,enum=EnumProto2,def=57005",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: (*EnumMessages)(nil),
 		Field:         10009,
 		Name:          "fizz.buzz.optional_message_v2",
 		Tag:           "bytes,10009,opt,name=optional_message_v2",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]bool)(nil),
 		Field:         10010,
 		Name:          "fizz.buzz.repeated_bool",
 		Tag:           "varint,10010,rep,name=repeated_bool",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]int32)(nil),
 		Field:         10011,
 		Name:          "fizz.buzz.repeated_int32",
 		Tag:           "varint,10011,rep,name=repeated_int32",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]uint32)(nil),
 		Field:         10012,
 		Name:          "fizz.buzz.repeated_uint32",
 		Tag:           "varint,10012,rep,name=repeated_uint32",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]float32)(nil),
 		Field:         10013,
 		Name:          "fizz.buzz.repeated_float",
 		Tag:           "fixed32,10013,rep,name=repeated_float",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]string)(nil),
 		Field:         10014,
 		Name:          "fizz.buzz.repeated_string",
 		Tag:           "bytes,10014,rep,name=repeated_string",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([][]byte)(nil),
 		Field:         10015,
 		Name:          "fizz.buzz.repeated_bytes",
 		Tag:           "bytes,10015,rep,name=repeated_bytes",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]proto2_20180125.Message_ChildEnum)(nil),
 		Field:         10016,
 		Name:          "fizz.buzz.repeated_enum_v1",
 		Tag:           "varint,10016,rep,name=repeated_enum_v1,enum=google.golang.org.proto2_20180125.Message_ChildEnum",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]*proto2_20180125.Message_ChildMessage)(nil),
 		Field:         10017,
 		Name:          "fizz.buzz.repeated_message_v1",
 		Tag:           "bytes,10017,rep,name=repeated_message_v1",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]EnumProto2)(nil),
 		Field:         10018,
 		Name:          "fizz.buzz.repeated_enum_v2",
 		Tag:           "varint,10018,rep,name=repeated_enum_v2,enum=EnumProto2",
+		Filename:      "test.proto",
 	}, {
-		ExtendedType:  (*legacyTestMessage)(nil),
+		ExtendedType:  (*LegacyTestMessage)(nil),
 		ExtensionType: ([]*EnumMessages)(nil),
 		Field:         10019,
 		Name:          "fizz.buzz.repeated_message_v2",
 		Tag:           "bytes,10019,rep,name=repeated_message_v2",
+		Filename:      "test.proto",
 	}}
 )
 
@@ -333,7 +340,7 @@
 		return x == y // pointer compare messages for object identity
 	})}
 
-	m := pimpl.Export{}.MessageOf(new(legacyTestMessage))
+	m := pimpl.Export{}.MessageOf(new(LegacyTestMessage))
 
 	if n := m.Len(); n != 0 {
 		t.Errorf("KnownFields.Len() = %v, want 0", n)
@@ -490,13 +497,6 @@
 					}
 					return out
 				}),
-				// TODO: Add this when ExtensionType no longer implements
-				// ExtensionDescriptor.
-				/*
-					cmp.Transformer("", func(x pref.ExtensionType) pref.ExtensionDescriptor {
-						return x.Descriptor()
-					}),
-				*/
 				cmp.Transformer("", func(x pref.Descriptor) map[string]interface{} {
 					out := make(map[string]interface{})
 					v := reflect.ValueOf(x)
@@ -558,6 +558,38 @@
 	Enum int32
 )
 
+func (*MessageA) Descriptor() ([]byte, []int) { return concurrentFD, []int{0} }
+func (*MessageB) Descriptor() ([]byte, []int) { return concurrentFD, []int{1} }
+func (Enum) EnumDescriptor() ([]byte, []int)  { return concurrentFD, []int{0} }
+
+var concurrentFD = func() []byte {
+	b, _ := proto.Marshal(pdesc.ToFileDescriptorProto(mustMakeFileDesc(`
+		name:    "concurrent.proto"
+		syntax:  "proto2"
+		package: "legacy"
+		message_type: [{
+			name: "MessageA"
+			field: [
+				{name:"a1" number:1 label:LABEL_REQUIRED type:TYPE_MESSAGE type_name:".legacy.MessageA"},
+				{name:"a2" number:2 label:LABEL_REQUIRED type:TYPE_MESSAGE type_name:".legacy.MessageB"},
+				{name:"a3" number:3 label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".legacy.Enum"}
+			]
+		}, {
+			name: "MessageB"
+			field: [
+				{name:"a1" number:1 label:LABEL_REQUIRED type:TYPE_MESSAGE type_name:".legacy.MessageA"},
+				{name:"a2" number:2 label:LABEL_REQUIRED type:TYPE_MESSAGE type_name:".legacy.MessageB"},
+				{name:"a3" number:3 label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".legacy.Enum"}
+			]
+		}]
+		enum_type: [{
+			name:  "Enum"
+			value: [{name:"FOO" number:500}]
+		}]
+	`, nil)))
+	return pimpl.Export{}.CompressGZIP(b)
+}()
+
 // TestConcurrentInit tests that concurrent wrapping of multiple legacy types
 // results in the exact same descriptor being created.
 func TestConcurrentInit(t *testing.T) {
diff --git a/internal/impl/message.go b/internal/impl/message.go
index df2fcee..161f194 100644
--- a/internal/impl/message.go
+++ b/internal/impl/message.go
@@ -283,6 +283,9 @@
 	if fx.Type == extensionFieldsType {
 		fieldOffset := offsetOf(fx)
 		mi.extensionMap = func(p pointer) *extensionMap {
+			if p.IsNil() {
+				return (*extensionMap)(nil)
+			}
 			v := p.Apply(fieldOffset).AsValueOf(extensionFieldsType)
 			return (*extensionMap)(v.Interface().(*map[int32]ExtensionField))
 		}
diff --git a/internal/impl/message_test.go b/internal/impl/message_test.go
index 722d1c0..fb89a2d 100644
--- a/internal/impl/message_test.go
+++ b/internal/impl/message_test.go
@@ -11,13 +11,15 @@
 	"strings"
 	"testing"
 
-	protoV1 "github.com/golang/protobuf/proto"
 	cmp "github.com/google/go-cmp/cmp"
 	cmpopts "github.com/google/go-cmp/cmp/cmpopts"
+	"google.golang.org/protobuf/encoding/prototext"
 	pimpl "google.golang.org/protobuf/internal/impl"
-	ptype "google.golang.org/protobuf/internal/prototype"
 	scalar "google.golang.org/protobuf/internal/scalar"
+	"google.golang.org/protobuf/proto"
+	pdesc "google.golang.org/protobuf/reflect/protodesc"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/reflect/protoregistry"
 	"google.golang.org/protobuf/reflect/prototype"
 
 	proto2_20180125 "google.golang.org/protobuf/internal/testprotos/legacy/proto2.v1.0.0-20180125-92554152"
@@ -158,20 +160,30 @@
 	MyBytesA  *MyString  `protobuf:"22"`
 }
 
-func mustMakeEnumDesc(t ptype.StandaloneEnum) pref.EnumDescriptor {
-	ed, err := ptype.NewEnum(&t)
+func mustMakeEnumDesc(path string, syntax pref.Syntax, enumDesc string) pref.EnumDescriptor {
+	s := fmt.Sprintf(`name:%q syntax:%q enum_type:[{%s}]`, path, syntax, enumDesc)
+	pb := new(descriptorpb.FileDescriptorProto)
+	if err := prototext.Unmarshal([]byte(s), pb); err != nil {
+		panic(err)
+	}
+	fd, err := pdesc.NewFile(pb, nil)
 	if err != nil {
 		panic(err)
 	}
-	return ed
+	return fd.Enums().Get(0)
 }
 
-func mustMakeMessageDesc(t ptype.StandaloneMessage) pref.MessageDescriptor {
-	md, err := ptype.NewMessage(&t)
+func mustMakeMessageDesc(path string, syntax pref.Syntax, fileDesc, msgDesc string, r pdesc.Resolver) pref.MessageDescriptor {
+	s := fmt.Sprintf(`name:%q syntax:%q %s message_type:[{%s}]`, path, syntax, fileDesc, msgDesc)
+	pb := new(descriptorpb.FileDescriptorProto)
+	if err := prototext.Unmarshal([]byte(s), pb); err != nil {
+		panic(err)
+	}
+	fd, err := pdesc.NewFile(pb, r)
 	if err != nil {
 		panic(err)
 	}
-	return md
+	return fd.Messages().Get(0)
 }
 
 var V = pref.ValueOf
@@ -196,35 +208,34 @@
 )
 
 var scalarProto2Type = pimpl.MessageInfo{GoType: reflect.TypeOf(new(ScalarProto2)), PBType: &prototype.Message{
-	MessageDescriptor: mustMakeMessageDesc(ptype.StandaloneMessage{
-		Syntax:   pref.Proto2,
-		FullName: "ScalarProto2",
-		Fields: []ptype.Field{
-			{Name: "f1", Number: 1, Cardinality: pref.Optional, Kind: pref.BoolKind, Default: V(bool(true))},
-			{Name: "f2", Number: 2, Cardinality: pref.Optional, Kind: pref.Int32Kind, Default: V(int32(2))},
-			{Name: "f3", Number: 3, Cardinality: pref.Optional, Kind: pref.Int64Kind, Default: V(int64(3))},
-			{Name: "f4", Number: 4, Cardinality: pref.Optional, Kind: pref.Uint32Kind, Default: V(uint32(4))},
-			{Name: "f5", Number: 5, Cardinality: pref.Optional, Kind: pref.Uint64Kind, Default: V(uint64(5))},
-			{Name: "f6", Number: 6, Cardinality: pref.Optional, Kind: pref.FloatKind, Default: V(float32(6))},
-			{Name: "f7", Number: 7, Cardinality: pref.Optional, Kind: pref.DoubleKind, Default: V(float64(7))},
-			{Name: "f8", Number: 8, Cardinality: pref.Optional, Kind: pref.StringKind, Default: V(string("8"))},
-			{Name: "f9", Number: 9, Cardinality: pref.Optional, Kind: pref.StringKind, Default: V(string("9"))},
-			{Name: "f10", Number: 10, Cardinality: pref.Optional, Kind: pref.BytesKind, Default: V([]byte("10"))},
-			{Name: "f11", Number: 11, Cardinality: pref.Optional, Kind: pref.BytesKind, Default: V([]byte("11"))},
+	MessageDescriptor: mustMakeMessageDesc("scalar2.proto", pref.Proto2, "", `
+		name: "ScalarProto2"
+		field: [
+			{name:"f1"  number:1  label:LABEL_OPTIONAL type:TYPE_BOOL   default_value:"true"},
+			{name:"f2"  number:2  label:LABEL_OPTIONAL type:TYPE_INT32  default_value:"2"},
+			{name:"f3"  number:3  label:LABEL_OPTIONAL type:TYPE_INT64  default_value:"3"},
+			{name:"f4"  number:4  label:LABEL_OPTIONAL type:TYPE_UINT32 default_value:"4"},
+			{name:"f5"  number:5  label:LABEL_OPTIONAL type:TYPE_UINT64 default_value:"5"},
+			{name:"f6"  number:6  label:LABEL_OPTIONAL type:TYPE_FLOAT  default_value:"6"},
+			{name:"f7"  number:7  label:LABEL_OPTIONAL type:TYPE_DOUBLE default_value:"7"},
+			{name:"f8"  number:8  label:LABEL_OPTIONAL type:TYPE_STRING default_value:"8"},
+			{name:"f9"  number:9  label:LABEL_OPTIONAL type:TYPE_STRING default_value:"9"},
+			{name:"f10" number:10 label:LABEL_OPTIONAL type:TYPE_BYTES  default_value:"10"},
+			{name:"f11" number:11 label:LABEL_OPTIONAL type:TYPE_BYTES  default_value:"11"},
 
-			{Name: "f12", Number: 12, Cardinality: pref.Optional, Kind: pref.BoolKind, Default: V(bool(true))},
-			{Name: "f13", Number: 13, Cardinality: pref.Optional, Kind: pref.Int32Kind, Default: V(int32(13))},
-			{Name: "f14", Number: 14, Cardinality: pref.Optional, Kind: pref.Int64Kind, Default: V(int64(14))},
-			{Name: "f15", Number: 15, Cardinality: pref.Optional, Kind: pref.Uint32Kind, Default: V(uint32(15))},
-			{Name: "f16", Number: 16, Cardinality: pref.Optional, Kind: pref.Uint64Kind, Default: V(uint64(16))},
-			{Name: "f17", Number: 17, Cardinality: pref.Optional, Kind: pref.FloatKind, Default: V(float32(17))},
-			{Name: "f18", Number: 18, Cardinality: pref.Optional, Kind: pref.DoubleKind, Default: V(float64(18))},
-			{Name: "f19", Number: 19, Cardinality: pref.Optional, Kind: pref.StringKind, Default: V(string("19"))},
-			{Name: "f20", Number: 20, Cardinality: pref.Optional, Kind: pref.StringKind, Default: V(string("20"))},
-			{Name: "f21", Number: 21, Cardinality: pref.Optional, Kind: pref.BytesKind, Default: V([]byte("21"))},
-			{Name: "f22", Number: 22, Cardinality: pref.Optional, Kind: pref.BytesKind, Default: V([]byte("22"))},
-		},
-	}),
+			{name:"f12" number:12 label:LABEL_OPTIONAL type:TYPE_BOOL   default_value:"true"},
+			{name:"f13" number:13 label:LABEL_OPTIONAL type:TYPE_INT32  default_value:"13"},
+			{name:"f14" number:14 label:LABEL_OPTIONAL type:TYPE_INT64  default_value:"14"},
+			{name:"f15" number:15 label:LABEL_OPTIONAL type:TYPE_UINT32 default_value:"15"},
+			{name:"f16" number:16 label:LABEL_OPTIONAL type:TYPE_UINT64 default_value:"16"},
+			{name:"f17" number:17 label:LABEL_OPTIONAL type:TYPE_FLOAT  default_value:"17"},
+			{name:"f18" number:18 label:LABEL_OPTIONAL type:TYPE_DOUBLE default_value:"18"},
+			{name:"f19" number:19 label:LABEL_OPTIONAL type:TYPE_STRING default_value:"19"},
+			{name:"f20" number:20 label:LABEL_OPTIONAL type:TYPE_STRING default_value:"20"},
+			{name:"f21" number:21 label:LABEL_OPTIONAL type:TYPE_BYTES  default_value:"21"},
+			{name:"f22" number:22 label:LABEL_OPTIONAL type:TYPE_BYTES  default_value:"22"}
+		]
+	`, nil),
 	NewMessage: func() pref.Message {
 		return pref.ProtoMessage(new(ScalarProto2)).ProtoReflect()
 	},
@@ -298,35 +309,34 @@
 }
 
 var scalarProto3Type = pimpl.MessageInfo{GoType: reflect.TypeOf(new(ScalarProto3)), PBType: &prototype.Message{
-	MessageDescriptor: mustMakeMessageDesc(ptype.StandaloneMessage{
-		Syntax:   pref.Proto3,
-		FullName: "ScalarProto3",
-		Fields: []ptype.Field{
-			{Name: "f1", Number: 1, Cardinality: pref.Optional, Kind: pref.BoolKind},
-			{Name: "f2", Number: 2, Cardinality: pref.Optional, Kind: pref.Int32Kind},
-			{Name: "f3", Number: 3, Cardinality: pref.Optional, Kind: pref.Int64Kind},
-			{Name: "f4", Number: 4, Cardinality: pref.Optional, Kind: pref.Uint32Kind},
-			{Name: "f5", Number: 5, Cardinality: pref.Optional, Kind: pref.Uint64Kind},
-			{Name: "f6", Number: 6, Cardinality: pref.Optional, Kind: pref.FloatKind},
-			{Name: "f7", Number: 7, Cardinality: pref.Optional, Kind: pref.DoubleKind},
-			{Name: "f8", Number: 8, Cardinality: pref.Optional, Kind: pref.StringKind},
-			{Name: "f9", Number: 9, Cardinality: pref.Optional, Kind: pref.StringKind},
-			{Name: "f10", Number: 10, Cardinality: pref.Optional, Kind: pref.BytesKind},
-			{Name: "f11", Number: 11, Cardinality: pref.Optional, Kind: pref.BytesKind},
+	MessageDescriptor: mustMakeMessageDesc("scalar3.proto", pref.Proto3, "", `
+		name: "ScalarProto3"
+		field: [
+			{name:"f1"  number:1  label:LABEL_OPTIONAL type:TYPE_BOOL},
+			{name:"f2"  number:2  label:LABEL_OPTIONAL type:TYPE_INT32},
+			{name:"f3"  number:3  label:LABEL_OPTIONAL type:TYPE_INT64},
+			{name:"f4"  number:4  label:LABEL_OPTIONAL type:TYPE_UINT32},
+			{name:"f5"  number:5  label:LABEL_OPTIONAL type:TYPE_UINT64},
+			{name:"f6"  number:6  label:LABEL_OPTIONAL type:TYPE_FLOAT},
+			{name:"f7"  number:7  label:LABEL_OPTIONAL type:TYPE_DOUBLE},
+			{name:"f8"  number:8  label:LABEL_OPTIONAL type:TYPE_STRING},
+			{name:"f9"  number:9  label:LABEL_OPTIONAL type:TYPE_STRING},
+			{name:"f10" number:10 label:LABEL_OPTIONAL type:TYPE_BYTES},
+			{name:"f11" number:11 label:LABEL_OPTIONAL type:TYPE_BYTES},
 
-			{Name: "f12", Number: 12, Cardinality: pref.Optional, Kind: pref.BoolKind},
-			{Name: "f13", Number: 13, Cardinality: pref.Optional, Kind: pref.Int32Kind},
-			{Name: "f14", Number: 14, Cardinality: pref.Optional, Kind: pref.Int64Kind},
-			{Name: "f15", Number: 15, Cardinality: pref.Optional, Kind: pref.Uint32Kind},
-			{Name: "f16", Number: 16, Cardinality: pref.Optional, Kind: pref.Uint64Kind},
-			{Name: "f17", Number: 17, Cardinality: pref.Optional, Kind: pref.FloatKind},
-			{Name: "f18", Number: 18, Cardinality: pref.Optional, Kind: pref.DoubleKind},
-			{Name: "f19", Number: 19, Cardinality: pref.Optional, Kind: pref.StringKind},
-			{Name: "f20", Number: 20, Cardinality: pref.Optional, Kind: pref.StringKind},
-			{Name: "f21", Number: 21, Cardinality: pref.Optional, Kind: pref.BytesKind},
-			{Name: "f22", Number: 22, Cardinality: pref.Optional, Kind: pref.BytesKind},
-		},
-	}),
+			{name:"f12" number:12 label:LABEL_OPTIONAL type:TYPE_BOOL},
+			{name:"f13" number:13 label:LABEL_OPTIONAL type:TYPE_INT32},
+			{name:"f14" number:14 label:LABEL_OPTIONAL type:TYPE_INT64},
+			{name:"f15" number:15 label:LABEL_OPTIONAL type:TYPE_UINT32},
+			{name:"f16" number:16 label:LABEL_OPTIONAL type:TYPE_UINT64},
+			{name:"f17" number:17 label:LABEL_OPTIONAL type:TYPE_FLOAT},
+			{name:"f18" number:18 label:LABEL_OPTIONAL type:TYPE_DOUBLE},
+			{name:"f19" number:19 label:LABEL_OPTIONAL type:TYPE_STRING},
+			{name:"f20" number:20 label:LABEL_OPTIONAL type:TYPE_STRING},
+			{name:"f21" number:21 label:LABEL_OPTIONAL type:TYPE_BYTES},
+			{name:"f22" number:22 label:LABEL_OPTIONAL type:TYPE_BYTES}
+		]
+	`, nil),
 	NewMessage: func() pref.Message {
 		return pref.ProtoMessage(new(ScalarProto3)).ProtoReflect()
 	},
@@ -418,33 +428,32 @@
 }
 
 var listScalarsType = pimpl.MessageInfo{GoType: reflect.TypeOf(new(ListScalars)), PBType: &prototype.Message{
-	MessageDescriptor: mustMakeMessageDesc(ptype.StandaloneMessage{
-		Syntax:   pref.Proto2,
-		FullName: "ListScalars",
-		Fields: []ptype.Field{
-			{Name: "f1", Number: 1, Cardinality: pref.Repeated, Kind: pref.BoolKind},
-			{Name: "f2", Number: 2, Cardinality: pref.Repeated, Kind: pref.Int32Kind},
-			{Name: "f3", Number: 3, Cardinality: pref.Repeated, Kind: pref.Int64Kind},
-			{Name: "f4", Number: 4, Cardinality: pref.Repeated, Kind: pref.Uint32Kind},
-			{Name: "f5", Number: 5, Cardinality: pref.Repeated, Kind: pref.Uint64Kind},
-			{Name: "f6", Number: 6, Cardinality: pref.Repeated, Kind: pref.FloatKind},
-			{Name: "f7", Number: 7, Cardinality: pref.Repeated, Kind: pref.DoubleKind},
-			{Name: "f8", Number: 8, Cardinality: pref.Repeated, Kind: pref.StringKind},
-			{Name: "f9", Number: 9, Cardinality: pref.Repeated, Kind: pref.StringKind},
-			{Name: "f10", Number: 10, Cardinality: pref.Repeated, Kind: pref.BytesKind},
-			{Name: "f11", Number: 11, Cardinality: pref.Repeated, Kind: pref.BytesKind},
+	MessageDescriptor: mustMakeMessageDesc("list-scalars.proto", pref.Proto2, "", `
+		name: "ListScalars"
+		field: [
+			{name:"f1"  number:1  label:LABEL_REPEATED type:TYPE_BOOL},
+			{name:"f2"  number:2  label:LABEL_REPEATED type:TYPE_INT32},
+			{name:"f3"  number:3  label:LABEL_REPEATED type:TYPE_INT64},
+			{name:"f4"  number:4  label:LABEL_REPEATED type:TYPE_UINT32},
+			{name:"f5"  number:5  label:LABEL_REPEATED type:TYPE_UINT64},
+			{name:"f6"  number:6  label:LABEL_REPEATED type:TYPE_FLOAT},
+			{name:"f7"  number:7  label:LABEL_REPEATED type:TYPE_DOUBLE},
+			{name:"f8"  number:8  label:LABEL_REPEATED type:TYPE_STRING},
+			{name:"f9"  number:9  label:LABEL_REPEATED type:TYPE_STRING},
+			{name:"f10" number:10 label:LABEL_REPEATED type:TYPE_BYTES},
+			{name:"f11" number:11 label:LABEL_REPEATED type:TYPE_BYTES},
 
-			{Name: "f12", Number: 12, Cardinality: pref.Repeated, Kind: pref.StringKind},
-			{Name: "f13", Number: 13, Cardinality: pref.Repeated, Kind: pref.StringKind},
-			{Name: "f14", Number: 14, Cardinality: pref.Repeated, Kind: pref.BytesKind},
-			{Name: "f15", Number: 15, Cardinality: pref.Repeated, Kind: pref.BytesKind},
+			{name:"f12" number:12 label:LABEL_REPEATED type:TYPE_STRING},
+			{name:"f13" number:13 label:LABEL_REPEATED type:TYPE_STRING},
+			{name:"f14" number:14 label:LABEL_REPEATED type:TYPE_BYTES},
+			{name:"f15" number:15 label:LABEL_REPEATED type:TYPE_BYTES},
 
-			{Name: "f16", Number: 16, Cardinality: pref.Repeated, Kind: pref.StringKind},
-			{Name: "f17", Number: 17, Cardinality: pref.Repeated, Kind: pref.StringKind},
-			{Name: "f18", Number: 18, Cardinality: pref.Repeated, Kind: pref.BytesKind},
-			{Name: "f19", Number: 19, Cardinality: pref.Repeated, Kind: pref.BytesKind},
-		},
-	}),
+			{name:"f16" number:16 label:LABEL_REPEATED type:TYPE_STRING},
+			{name:"f17" number:17 label:LABEL_REPEATED type:TYPE_STRING},
+			{name:"f18" number:18 label:LABEL_REPEATED type:TYPE_BYTES},
+			{name:"f19" number:19 label:LABEL_REPEATED type:TYPE_BYTES}
+		]
+	`, nil),
 	NewMessage: func() pref.Message {
 		return pref.ProtoMessage(new(ListScalars)).ProtoReflect()
 	},
@@ -575,60 +584,70 @@
 	MyBytes4   MapStrings `protobuf:"25"`
 }
 
-func mustMakeMapEntry(n pref.FieldNumber, keyKind, valKind pref.Kind) ptype.Field {
-	return ptype.Field{
-		Name:        pref.Name(fmt.Sprintf("f%d", n)),
-		Number:      n,
-		Cardinality: pref.Repeated,
-		Kind:        pref.MessageKind,
-		MessageType: mustMakeMessageDesc(ptype.StandaloneMessage{
-			Syntax:   pref.Proto2,
-			FullName: pref.FullName(fmt.Sprintf("MapScalars.F%dEntry", n)),
-			Fields: []ptype.Field{
-				{Name: "key", Number: 1, Cardinality: pref.Optional, Kind: keyKind},
-				{Name: "value", Number: 2, Cardinality: pref.Optional, Kind: valKind},
-			},
-			Options:    &descriptorpb.MessageOptions{MapEntry: scalar.Bool(true)},
-			IsMapEntry: true,
-		}),
-	}
-}
-
 var mapScalarsType = pimpl.MessageInfo{GoType: reflect.TypeOf(new(MapScalars)), PBType: &prototype.Message{
-	MessageDescriptor: mustMakeMessageDesc(ptype.StandaloneMessage{
-		Syntax:   pref.Proto2,
-		FullName: "MapScalars",
-		Fields: []ptype.Field{
-			mustMakeMapEntry(1, pref.BoolKind, pref.StringKind),
-			mustMakeMapEntry(2, pref.Int32Kind, pref.StringKind),
-			mustMakeMapEntry(3, pref.Int64Kind, pref.StringKind),
-			mustMakeMapEntry(4, pref.Uint32Kind, pref.StringKind),
-			mustMakeMapEntry(5, pref.Uint64Kind, pref.StringKind),
-			mustMakeMapEntry(6, pref.StringKind, pref.StringKind),
+	MessageDescriptor: mustMakeMessageDesc("map-scalars.proto", pref.Proto2, "", `
+		name: "MapScalars"
+		field: [
+			{name:"f1"  number:1  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F1Entry"},
+			{name:"f2"  number:2  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F2Entry"},
+			{name:"f3"  number:3  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F3Entry"},
+			{name:"f4"  number:4  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F4Entry"},
+			{name:"f5"  number:5  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F5Entry"},
+			{name:"f6"  number:6  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F6Entry"},
 
-			mustMakeMapEntry(7, pref.StringKind, pref.BoolKind),
-			mustMakeMapEntry(8, pref.StringKind, pref.Int32Kind),
-			mustMakeMapEntry(9, pref.StringKind, pref.Int64Kind),
-			mustMakeMapEntry(10, pref.StringKind, pref.Uint32Kind),
-			mustMakeMapEntry(11, pref.StringKind, pref.Uint64Kind),
-			mustMakeMapEntry(12, pref.StringKind, pref.FloatKind),
-			mustMakeMapEntry(13, pref.StringKind, pref.DoubleKind),
-			mustMakeMapEntry(14, pref.StringKind, pref.StringKind),
-			mustMakeMapEntry(15, pref.StringKind, pref.StringKind),
-			mustMakeMapEntry(16, pref.StringKind, pref.BytesKind),
-			mustMakeMapEntry(17, pref.StringKind, pref.BytesKind),
+			{name:"f7"  number:7  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F7Entry"},
+			{name:"f8"  number:8  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F8Entry"},
+			{name:"f9"  number:9  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F9Entry"},
+			{name:"f10" number:10 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F10Entry"},
+			{name:"f11" number:11 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F11Entry"},
+			{name:"f12" number:12 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F12Entry"},
+			{name:"f13" number:13 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F13Entry"},
+			{name:"f14" number:14 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F14Entry"},
+			{name:"f15" number:15 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F15Entry"},
+			{name:"f16" number:16 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F16Entry"},
+			{name:"f17" number:17 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F17Entry"},
 
-			mustMakeMapEntry(18, pref.StringKind, pref.StringKind),
-			mustMakeMapEntry(19, pref.StringKind, pref.StringKind),
-			mustMakeMapEntry(20, pref.StringKind, pref.BytesKind),
-			mustMakeMapEntry(21, pref.StringKind, pref.BytesKind),
+			{name:"f18" number:18 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F18Entry"},
+			{name:"f19" number:19 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F19Entry"},
+			{name:"f20" number:20 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F20Entry"},
+			{name:"f21" number:21 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F21Entry"},
 
-			mustMakeMapEntry(22, pref.StringKind, pref.StringKind),
-			mustMakeMapEntry(23, pref.StringKind, pref.StringKind),
-			mustMakeMapEntry(24, pref.StringKind, pref.BytesKind),
-			mustMakeMapEntry(25, pref.StringKind, pref.BytesKind),
-		},
-	}),
+			{name:"f22" number:22 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F22Entry"},
+			{name:"f23" number:23 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F23Entry"},
+			{name:"f24" number:24 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F24Entry"},
+			{name:"f25" number:25 label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".MapScalars.F25Entry"}
+		]
+		nested_type: [
+			{name:"F1Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_BOOL},   {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F2Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_INT32},  {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F3Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_INT64},  {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F4Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_UINT32}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F5Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_UINT64}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F6Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+
+			{name:"F7Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_BOOL}]   options:{map_entry:true}},
+			{name:"F8Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_INT32}]  options:{map_entry:true}},
+			{name:"F9Entry"  field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_INT64}]  options:{map_entry:true}},
+			{name:"F10Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_UINT32}] options:{map_entry:true}},
+			{name:"F11Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_UINT64}] options:{map_entry:true}},
+			{name:"F12Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_FLOAT}]  options:{map_entry:true}},
+			{name:"F13Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_DOUBLE}] options:{map_entry:true}},
+			{name:"F14Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F15Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F16Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_BYTES}]  options:{map_entry:true}},
+			{name:"F17Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_BYTES}]  options:{map_entry:true}},
+
+			{name:"F18Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F19Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F20Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_BYTES}]  options:{map_entry:true}},
+			{name:"F21Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_BYTES}]  options:{map_entry:true}},
+
+			{name:"F22Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F23Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_STRING}] options:{map_entry:true}},
+			{name:"F24Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_BYTES}]  options:{map_entry:true}},
+			{name:"F25Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_BYTES}]  options:{map_entry:true}}
+		]
+	`, nil),
 	NewMessage: func() pref.Message {
 		return pref.ProtoMessage(new(MapScalars)).ProtoReflect()
 	},
@@ -760,26 +779,25 @@
 }
 
 var oneofScalarsType = pimpl.MessageInfo{GoType: reflect.TypeOf(new(OneofScalars)), PBType: &prototype.Message{
-	MessageDescriptor: mustMakeMessageDesc(ptype.StandaloneMessage{
-		Syntax:   pref.Proto2,
-		FullName: "OneofScalars",
-		Fields: []ptype.Field{
-			{Name: "f1", Number: 1, Cardinality: pref.Optional, Kind: pref.BoolKind, Default: V(bool(true)), OneofName: "union"},
-			{Name: "f2", Number: 2, Cardinality: pref.Optional, Kind: pref.Int32Kind, Default: V(int32(2)), OneofName: "union"},
-			{Name: "f3", Number: 3, Cardinality: pref.Optional, Kind: pref.Int64Kind, Default: V(int64(3)), OneofName: "union"},
-			{Name: "f4", Number: 4, Cardinality: pref.Optional, Kind: pref.Uint32Kind, Default: V(uint32(4)), OneofName: "union"},
-			{Name: "f5", Number: 5, Cardinality: pref.Optional, Kind: pref.Uint64Kind, Default: V(uint64(5)), OneofName: "union"},
-			{Name: "f6", Number: 6, Cardinality: pref.Optional, Kind: pref.FloatKind, Default: V(float32(6)), OneofName: "union"},
-			{Name: "f7", Number: 7, Cardinality: pref.Optional, Kind: pref.DoubleKind, Default: V(float64(7)), OneofName: "union"},
-			{Name: "f8", Number: 8, Cardinality: pref.Optional, Kind: pref.StringKind, Default: V(string("8")), OneofName: "union"},
-			{Name: "f9", Number: 9, Cardinality: pref.Optional, Kind: pref.StringKind, Default: V(string("9")), OneofName: "union"},
-			{Name: "f10", Number: 10, Cardinality: pref.Optional, Kind: pref.StringKind, Default: V(string("10")), OneofName: "union"},
-			{Name: "f11", Number: 11, Cardinality: pref.Optional, Kind: pref.BytesKind, Default: V([]byte("11")), OneofName: "union"},
-			{Name: "f12", Number: 12, Cardinality: pref.Optional, Kind: pref.BytesKind, Default: V([]byte("12")), OneofName: "union"},
-			{Name: "f13", Number: 13, Cardinality: pref.Optional, Kind: pref.BytesKind, Default: V([]byte("13")), OneofName: "union"},
-		},
-		Oneofs: []ptype.Oneof{{Name: "union"}},
-	}),
+	MessageDescriptor: mustMakeMessageDesc("oneof-scalars.proto", pref.Proto2, "", `
+		name: "OneofScalars"
+		field: [
+			{name:"f1"  number:1  label:LABEL_OPTIONAL type:TYPE_BOOL   default_value:"true" oneof_index:0},
+			{name:"f2"  number:2  label:LABEL_OPTIONAL type:TYPE_INT32  default_value:"2"    oneof_index:0},
+			{name:"f3"  number:3  label:LABEL_OPTIONAL type:TYPE_INT64  default_value:"3"    oneof_index:0},
+			{name:"f4"  number:4  label:LABEL_OPTIONAL type:TYPE_UINT32 default_value:"4"    oneof_index:0},
+			{name:"f5"  number:5  label:LABEL_OPTIONAL type:TYPE_UINT64 default_value:"5"    oneof_index:0},
+			{name:"f6"  number:6  label:LABEL_OPTIONAL type:TYPE_FLOAT  default_value:"6"    oneof_index:0},
+			{name:"f7"  number:7  label:LABEL_OPTIONAL type:TYPE_DOUBLE default_value:"7"    oneof_index:0},
+			{name:"f8"  number:8  label:LABEL_OPTIONAL type:TYPE_STRING default_value:"8"    oneof_index:0},
+			{name:"f9"  number:9  label:LABEL_OPTIONAL type:TYPE_STRING default_value:"9"    oneof_index:0},
+			{name:"f10" number:10 label:LABEL_OPTIONAL type:TYPE_STRING default_value:"10"   oneof_index:0},
+			{name:"f11" number:11 label:LABEL_OPTIONAL type:TYPE_BYTES  default_value:"11"   oneof_index:0},
+			{name:"f12" number:12 label:LABEL_OPTIONAL type:TYPE_BYTES  default_value:"12"   oneof_index:0},
+			{name:"f13" number:13 label:LABEL_OPTIONAL type:TYPE_BYTES  default_value:"13"   oneof_index:0}
+		]
+		oneof_decl: [{name:"union"}]
+	`, nil),
 	NewMessage: func() pref.Message {
 		return pref.ProtoMessage(new(OneofScalars)).ProtoReflect()
 	},
@@ -923,11 +941,10 @@
 type EnumProto2 int32
 
 var enumProto2Type = &prototype.Enum{
-	EnumDescriptor: mustMakeEnumDesc(ptype.StandaloneEnum{
-		Syntax:   pref.Proto2,
-		FullName: "EnumProto2",
-		Values:   []ptype.EnumValue{{Name: "DEAD", Number: 0xdead}, {Name: "BEEF", Number: 0xbeef}},
-	}),
+	EnumDescriptor: mustMakeEnumDesc("enum2.proto", pref.Proto2, `
+		name:  "EnumProto2"
+		value: [{name:"DEAD" number:0xdead}, {name:"BEEF" number:0xbeef}]
+	`),
 	NewEnum: func(n pref.EnumNumber) pref.Enum {
 		return EnumProto2(n)
 	},
@@ -940,11 +957,10 @@
 type EnumProto3 int32
 
 var enumProto3Type = &prototype.Enum{
-	EnumDescriptor: mustMakeEnumDesc(ptype.StandaloneEnum{
-		Syntax:   pref.Proto3,
-		FullName: "EnumProto3",
-		Values:   []ptype.EnumValue{{Name: "ALPHA", Number: 0}, {Name: "BRAVO", Number: 1}},
-	}),
+	EnumDescriptor: mustMakeEnumDesc("enum3.proto", pref.Proto3, `
+		name:  "EnumProto3",
+		value: [{name:"ALPHA" number:0}, {name:"BRAVO" number:1}]
+	`),
 	NewEnum: func(n pref.EnumNumber) pref.Enum {
 		return EnumProto3(n)
 	},
@@ -967,52 +983,41 @@
 }
 
 var enumMessagesType = pimpl.MessageInfo{GoType: reflect.TypeOf(new(EnumMessages)), PBType: &prototype.Message{
-	MessageDescriptor: mustMakeMessageDesc(ptype.StandaloneMessage{
-		Syntax:   pref.Proto2,
-		FullName: "EnumMessages",
-		Fields: []ptype.Field{
-			{Name: "f1", Number: 1, Cardinality: pref.Optional, Kind: pref.EnumKind, Default: V("BEEF"), EnumType: enumProto2Type.Descriptor()},
-			{Name: "f2", Number: 2, Cardinality: pref.Optional, Kind: pref.EnumKind, Default: V("BRAVO"), EnumType: enumProto3Type.Descriptor()},
-			{Name: "f3", Number: 3, Cardinality: pref.Optional, Kind: pref.MessageKind, MessageType: pimpl.Export{}.MessageDescriptorOf(new(proto2_20180125.Message))},
-			{Name: "f4", Number: 4, Cardinality: pref.Optional, Kind: pref.MessageKind, MessageType: ptype.PlaceholderMessage("EnumMessages")},
-			{Name: "f5", Number: 5, Cardinality: pref.Repeated, Kind: pref.EnumKind, EnumType: enumProto2Type.Descriptor()},
-			{Name: "f6", Number: 6, Cardinality: pref.Repeated, Kind: pref.MessageKind, MessageType: scalarProto2Type.PBType.Descriptor()},
-			{Name: "f7", Number: 7, Cardinality: pref.Repeated, Kind: pref.MessageKind, MessageType: enumMapDesc},
-			{Name: "f8", Number: 8, Cardinality: pref.Repeated, Kind: pref.MessageKind, MessageType: messageMapDesc},
-			{Name: "f9", Number: 9, Cardinality: pref.Optional, Kind: pref.EnumKind, Default: V("BEEF"), OneofName: "union", EnumType: enumProto2Type.Descriptor()},
-			{Name: "f10", Number: 10, Cardinality: pref.Optional, Kind: pref.EnumKind, Default: V("BRAVO"), OneofName: "union", EnumType: enumProto3Type.Descriptor()},
-			{Name: "f11", Number: 11, Cardinality: pref.Optional, Kind: pref.MessageKind, OneofName: "union", MessageType: scalarProto2Type.PBType.Descriptor()},
-			{Name: "f12", Number: 12, Cardinality: pref.Optional, Kind: pref.MessageKind, OneofName: "union", MessageType: scalarProto3Type.PBType.Descriptor()},
-		},
-		Oneofs: []ptype.Oneof{{Name: "union"}},
-	}),
+	MessageDescriptor: mustMakeMessageDesc("enum-messages.proto", pref.Proto2, `
+		dependency: ["enum2.proto", "enum3.proto", "scalar2.proto", "scalar3.proto", "proto2.v1.0.0-20180125-92554152/test.proto"]
+	`, `
+		name: "EnumMessages"
+		field: [
+			{name:"f1"  number:1  label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".EnumProto2" default_value:"BEEF"},
+			{name:"f2"  number:2  label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".EnumProto3" default_value:"BRAVO"},
+			{name:"f3"  number:3  label:LABEL_OPTIONAL type:TYPE_MESSAGE type_Name:".google.golang.org.proto2_20180125.Message"},
+			{name:"f4"  number:4  label:LABEL_OPTIONAL type:TYPE_MESSAGE type_Name:".EnumMessages"},
+			{name:"f5"  number:5  label:LABEL_REPEATED type:TYPE_ENUM    type_name:".EnumProto2"},
+			{name:"f6"  number:6  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".ScalarProto2"},
+			{name:"f7"  number:7  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".EnumMessages.F7Entry"},
+			{name:"f8"  number:8  label:LABEL_REPEATED type:TYPE_MESSAGE type_name:".EnumMessages.F8Entry"},
+			{name:"f9"  number:9  label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".EnumProto2"   oneof_index:0 default_value:"BEEF"},
+			{name:"f10" number:10 label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".EnumProto3"   oneof_index:0 default_value:"BRAVO"},
+			{name:"f11" number:11 label:LABEL_OPTIONAL type:TYPE_MESSAGE type_name:".ScalarProto2" oneof_index:0},
+			{name:"f12" number:12 label:LABEL_OPTIONAL type:TYPE_MESSAGE type_name:".ScalarProto3" oneof_index:0}
+		]
+		oneof_decl: [{name:"union"}]
+		nested_type: [
+			{name:"F7Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_ENUM    type_name:".EnumProto3"}]   options:{map_entry:true}},
+			{name:"F8Entry" field:[{name:"key" number:1 label:LABEL_OPTIONAL type:TYPE_STRING}, {name:"value" number:2 label:LABEL_OPTIONAL type:TYPE_MESSAGE type_name:".ScalarProto3"}] options:{map_entry:true}}
+		]
+	`, protoregistry.NewFiles(
+		EnumProto2(0).Descriptor().ParentFile(),
+		EnumProto3(0).Descriptor().ParentFile(),
+		((*ScalarProto2)(nil)).ProtoReflect().Descriptor().ParentFile(),
+		((*ScalarProto3)(nil)).ProtoReflect().Descriptor().ParentFile(),
+		pimpl.Export{}.MessageDescriptorOf((*proto2_20180125.Message)(nil)).ParentFile(),
+	)),
 	NewMessage: func() pref.Message {
 		return pref.ProtoMessage(new(EnumMessages)).ProtoReflect()
 	},
 }}
 
-var enumMapDesc = mustMakeMessageDesc(ptype.StandaloneMessage{
-	Syntax:   pref.Proto2,
-	FullName: "EnumMessages.F7Entry",
-	Fields: []ptype.Field{
-		{Name: "key", Number: 1, Cardinality: pref.Optional, Kind: pref.StringKind},
-		{Name: "value", Number: 2, Cardinality: pref.Optional, Kind: pref.EnumKind, EnumType: enumProto3Type.Descriptor()},
-	},
-	Options:    &descriptorpb.MessageOptions{MapEntry: scalar.Bool(true)},
-	IsMapEntry: true,
-})
-
-var messageMapDesc = mustMakeMessageDesc(ptype.StandaloneMessage{
-	Syntax:   pref.Proto2,
-	FullName: "EnumMessages.F8Entry",
-	Fields: []ptype.Field{
-		{Name: "key", Number: 1, Cardinality: pref.Optional, Kind: pref.StringKind},
-		{Name: "value", Number: 2, Cardinality: pref.Optional, Kind: pref.MessageKind, MessageType: scalarProto3Type.PBType.Descriptor()},
-	},
-	Options:    &descriptorpb.MessageOptions{MapEntry: scalar.Bool(true)},
-	IsMapEntry: true,
-})
-
 func (m *EnumMessages) ProtoReflect() pref.Message { return enumMessagesType.MessageOf(m) }
 
 func (*EnumMessages) XXX_OneofWrappers() []interface{} {
@@ -1161,7 +1166,9 @@
 
 var cmpOpts = cmp.Options{
 	cmp.Comparer(func(x, y *proto2_20180125.Message) bool {
-		return protoV1.Equal(x, y)
+		mx := pimpl.Export{}.MessageOf(x).Interface()
+		my := pimpl.Export{}.MessageOf(y).Interface()
+		return proto.Equal(mx, my)
 	}),
 	cmp.Transformer("UnwrapValue", func(pv pref.Value) interface{} {
 		switch v := pv.Interface().(type) {