internal/strs: unify string manipulation functionality

Create a new internal/strs package that unifies common functionality:
* Since protobuf itself pseudo-specifies at least 4 different camel-case
and snake-case conversion functions, we define all variants in one place.
* We move the internal/filedesc.nameBuilder function to this package.
We simplify its implementation to not depend on a strings.Builder fork
under the hood since the semantics we desire is simpler than what
strings.Builder provides.
* We use strs.Builder in reflect/protodesc in its construction of all
the full names. This is perfect use case of strs.Builder since all
full names within a file descriptor share the same lifetime.
* Add an UnsafeString and UnsafeBytes cast function that will be useful
in the near future for optimizing encoding/prototext and encoding/protojson.

Change-Id: I2cf07cbaf6f72e5f9fd6ae3d37b0d46f6af2ad59
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/185198
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/filedesc/desc.go b/internal/filedesc/desc.go
index 84c90fa..20ffd83 100644
--- a/internal/filedesc/desc.go
+++ b/internal/filedesc/desc.go
@@ -14,6 +14,7 @@
 	"google.golang.org/protobuf/internal/descopts"
 	"google.golang.org/protobuf/internal/encoding/defval"
 	"google.golang.org/protobuf/internal/pragma"
+	"google.golang.org/protobuf/internal/strs"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 )
 
@@ -465,30 +466,12 @@
 func (js *jsonName) get(fd pref.FieldDescriptor) string {
 	if !js.has {
 		js.once.Do(func() {
-			js.name = makeJSONName(fd.Name())
+			js.name = strs.JSONCamelCase(string(fd.Name()))
 		})
 	}
 	return js.name
 }
 
-// makeJSONName creates a JSON name from the protobuf short name.
-func makeJSONName(s pref.Name) string {
-	var b []byte
-	var wasUnderscore bool
-	for i := 0; i < len(s); i++ { // proto identifiers are always ASCII
-		c := s[i]
-		if c != '_' {
-			isLower := 'a' <= c && c <= 'z'
-			if wasUnderscore && isLower {
-				c -= 'a' - 'A'
-			}
-			b = append(b, c)
-		}
-		wasUnderscore = c == '_'
-	}
-	return string(b)
-}
-
 func DefaultValue(v pref.Value, ev pref.EnumValueDescriptor) defaultValue {
 	dv := defaultValue{has: v.IsValid(), val: v, enum: ev}
 	if b, ok := v.Interface().([]byte); ok {
diff --git a/internal/filedesc/desc_init.go b/internal/filedesc/desc_init.go
index a51a7ec..0bd7d38 100644
--- a/internal/filedesc/desc_init.go
+++ b/internal/filedesc/desc_init.go
@@ -5,8 +5,11 @@
 package filedesc
 
 import (
+	"sync"
+
 	"google.golang.org/protobuf/internal/encoding/wire"
 	"google.golang.org/protobuf/internal/fieldnum"
+	"google.golang.org/protobuf/internal/strs"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 )
 
@@ -89,8 +92,8 @@
 }
 
 func (fd *File) unmarshalSeed(b []byte) {
-	nb := getNameBuilder()
-	defer putNameBuilder(nb)
+	sb := getBuilder()
+	defer putBuilder(sb)
 
 	var prevField pref.FieldNumber
 	var numEnums, numMessages, numExtensions, numServices int
@@ -114,9 +117,9 @@
 					panic("invalid syntax")
 				}
 			case fieldnum.FileDescriptorProto_Name:
-				fd.L1.Path = nb.MakeString(v)
+				fd.L1.Path = sb.MakeString(v)
 			case fieldnum.FileDescriptorProto_Package:
-				fd.L1.Package = pref.FullName(nb.MakeString(v))
+				fd.L1.Package = pref.FullName(sb.MakeString(v))
 			case fieldnum.FileDescriptorProto_EnumType:
 				if prevField != fieldnum.FileDescriptorProto_EnumType {
 					if numEnums > 0 {
@@ -183,7 +186,7 @@
 		for i := range fd.L1.Enums.List {
 			_, n := wire.ConsumeVarint(b)
 			v, m := wire.ConsumeBytes(b[n:])
-			fd.L1.Enums.List[i].unmarshalSeed(v, nb, fd, fd, i)
+			fd.L1.Enums.List[i].unmarshalSeed(v, sb, fd, fd, i)
 			b = b[n+m:]
 		}
 	}
@@ -192,7 +195,7 @@
 		for i := range fd.L1.Messages.List {
 			_, n := wire.ConsumeVarint(b)
 			v, m := wire.ConsumeBytes(b[n:])
-			fd.L1.Messages.List[i].unmarshalSeed(v, nb, fd, fd, i)
+			fd.L1.Messages.List[i].unmarshalSeed(v, sb, fd, fd, i)
 			b = b[n+m:]
 		}
 	}
@@ -201,7 +204,7 @@
 		for i := range fd.L1.Extensions.List {
 			_, n := wire.ConsumeVarint(b)
 			v, m := wire.ConsumeBytes(b[n:])
-			fd.L1.Extensions.List[i].unmarshalSeed(v, nb, fd, fd, i)
+			fd.L1.Extensions.List[i].unmarshalSeed(v, sb, fd, fd, i)
 			b = b[n+m:]
 		}
 	}
@@ -210,13 +213,13 @@
 		for i := range fd.L1.Services.List {
 			_, n := wire.ConsumeVarint(b)
 			v, m := wire.ConsumeBytes(b[n:])
-			fd.L1.Services.List[i].unmarshalSeed(v, nb, fd, fd, i)
+			fd.L1.Services.List[i].unmarshalSeed(v, sb, fd, fd, i)
 			b = b[n+m:]
 		}
 	}
 }
 
-func (ed *Enum) unmarshalSeed(b []byte, nb *nameBuilder, pf *File, pd pref.Descriptor, i int) {
+func (ed *Enum) unmarshalSeed(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
 	ed.L0.ParentFile = pf
 	ed.L0.Parent = pd
 	ed.L0.Index = i
@@ -231,7 +234,7 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.EnumDescriptorProto_Name:
-				ed.L0.FullName = nb.AppendFullName(pd.FullName(), v)
+				ed.L0.FullName = appendFullName(sb, pd.FullName(), v)
 			case fieldnum.EnumDescriptorProto_Value:
 				numValues++
 			}
@@ -258,7 +261,7 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.EnumDescriptorProto_Value:
-				ed.L2.Values.List[i].unmarshalFull(v, nb, pf, ed, i)
+				ed.L2.Values.List[i].unmarshalFull(v, sb, pf, ed, i)
 				i++
 			}
 		default:
@@ -268,7 +271,7 @@
 	}
 }
 
-func (md *Message) unmarshalSeed(b []byte, nb *nameBuilder, pf *File, pd pref.Descriptor, i int) {
+func (md *Message) unmarshalSeed(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
 	md.L0.ParentFile = pf
 	md.L0.Parent = pd
 	md.L0.Index = i
@@ -286,7 +289,7 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.DescriptorProto_Name:
-				md.L0.FullName = nb.AppendFullName(pd.FullName(), v)
+				md.L0.FullName = appendFullName(sb, pd.FullName(), v)
 			case fieldnum.DescriptorProto_EnumType:
 				if prevField != fieldnum.DescriptorProto_EnumType {
 					if numEnums > 0 {
@@ -337,7 +340,7 @@
 		for i := range md.L1.Enums.List {
 			_, n := wire.ConsumeVarint(b)
 			v, m := wire.ConsumeBytes(b[n:])
-			md.L1.Enums.List[i].unmarshalSeed(v, nb, pf, md, i)
+			md.L1.Enums.List[i].unmarshalSeed(v, sb, pf, md, i)
 			b = b[n+m:]
 		}
 	}
@@ -346,7 +349,7 @@
 		for i := range md.L1.Messages.List {
 			_, n := wire.ConsumeVarint(b)
 			v, m := wire.ConsumeBytes(b[n:])
-			md.L1.Messages.List[i].unmarshalSeed(v, nb, pf, md, i)
+			md.L1.Messages.List[i].unmarshalSeed(v, sb, pf, md, i)
 			b = b[n+m:]
 		}
 	}
@@ -355,13 +358,13 @@
 		for i := range md.L1.Extensions.List {
 			_, n := wire.ConsumeVarint(b)
 			v, m := wire.ConsumeBytes(b[n:])
-			md.L1.Extensions.List[i].unmarshalSeed(v, nb, pf, md, i)
+			md.L1.Extensions.List[i].unmarshalSeed(v, sb, pf, md, i)
 			b = b[n+m:]
 		}
 	}
 }
 
-func (xd *Extension) unmarshalSeed(b []byte, nb *nameBuilder, pf *File, pd pref.Descriptor, i int) {
+func (xd *Extension) unmarshalSeed(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
 	xd.L0.ParentFile = pf
 	xd.L0.Parent = pd
 	xd.L0.Index = i
@@ -384,9 +387,9 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.FieldDescriptorProto_Name:
-				xd.L0.FullName = nb.AppendFullName(pd.FullName(), v)
+				xd.L0.FullName = appendFullName(sb, pd.FullName(), v)
 			case fieldnum.FieldDescriptorProto_Extendee:
-				xd.L1.Extendee = PlaceholderMessage(nb.MakeFullName(v))
+				xd.L1.Extendee = PlaceholderMessage(makeFullName(sb, v))
 			}
 		default:
 			m := wire.ConsumeFieldValue(num, typ, b)
@@ -395,7 +398,7 @@
 	}
 }
 
-func (sd *Service) unmarshalSeed(b []byte, nb *nameBuilder, pf *File, pd pref.Descriptor, i int) {
+func (sd *Service) unmarshalSeed(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
 	sd.L0.ParentFile = pf
 	sd.L0.Parent = pd
 	sd.L0.Index = i
@@ -409,7 +412,7 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.ServiceDescriptorProto_Name:
-				sd.L0.FullName = nb.AppendFullName(pd.FullName(), v)
+				sd.L0.FullName = appendFullName(sb, pd.FullName(), v)
 			}
 		default:
 			m := wire.ConsumeFieldValue(num, typ, b)
@@ -417,3 +420,27 @@
 		}
 	}
 }
+
+var nameBuilderPool = sync.Pool{
+	New: func() interface{} { return new(strs.Builder) },
+}
+
+func getBuilder() *strs.Builder {
+	return nameBuilderPool.Get().(*strs.Builder)
+}
+func putBuilder(b *strs.Builder) {
+	nameBuilderPool.Put(b)
+}
+
+// makeFullName converts b to a protoreflect.FullName,
+// where b must start with a leading dot.
+func makeFullName(sb *strs.Builder, b []byte) pref.FullName {
+	if len(b) == 0 || b[0] != '.' {
+		panic("name reference must be fully qualified")
+	}
+	return pref.FullName(sb.MakeString(b[1:]))
+}
+
+func appendFullName(sb *strs.Builder, prefix pref.FullName, suffix []byte) pref.FullName {
+	return sb.AppendFullName(prefix, pref.Name(strs.UnsafeString(suffix)))
+}
diff --git a/internal/filedesc/desc_lazy.go b/internal/filedesc/desc_lazy.go
index 4d31109..55104ad 100644
--- a/internal/filedesc/desc_lazy.go
+++ b/internal/filedesc/desc_lazy.go
@@ -11,6 +11,7 @@
 	"google.golang.org/protobuf/internal/descopts"
 	"google.golang.org/protobuf/internal/encoding/wire"
 	"google.golang.org/protobuf/internal/fieldnum"
+	"google.golang.org/protobuf/internal/strs"
 	"google.golang.org/protobuf/proto"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
 )
@@ -132,8 +133,8 @@
 }
 
 func (fd *File) unmarshalFull(b []byte) {
-	nb := getNameBuilder()
-	defer putNameBuilder(nb)
+	sb := getBuilder()
+	defer putBuilder(sb)
 
 	var enumIdx, messageIdx, extensionIdx, serviceIdx int
 	var rawOptions []byte
@@ -156,23 +157,23 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.FileDescriptorProto_Dependency:
-				path := nb.MakeString(v)
+				path := sb.MakeString(v)
 				imp, _ := fd.builder.FileRegistry.FindFileByPath(path)
 				if imp == nil {
 					imp = PlaceholderFile(path)
 				}
 				fd.L2.Imports = append(fd.L2.Imports, pref.FileImport{FileDescriptor: imp})
 			case fieldnum.FileDescriptorProto_EnumType:
-				fd.L1.Enums.List[enumIdx].unmarshalFull(v, nb)
+				fd.L1.Enums.List[enumIdx].unmarshalFull(v, sb)
 				enumIdx++
 			case fieldnum.FileDescriptorProto_MessageType:
-				fd.L1.Messages.List[messageIdx].unmarshalFull(v, nb)
+				fd.L1.Messages.List[messageIdx].unmarshalFull(v, sb)
 				messageIdx++
 			case fieldnum.FileDescriptorProto_Extension:
-				fd.L1.Extensions.List[extensionIdx].unmarshalFull(v, nb)
+				fd.L1.Extensions.List[extensionIdx].unmarshalFull(v, sb)
 				extensionIdx++
 			case fieldnum.FileDescriptorProto_Service:
-				fd.L1.Services.List[serviceIdx].unmarshalFull(v, nb)
+				fd.L1.Services.List[serviceIdx].unmarshalFull(v, sb)
 				serviceIdx++
 			case fieldnum.FileDescriptorProto_Options:
 				rawOptions = appendOptions(rawOptions, v)
@@ -185,7 +186,7 @@
 	fd.L2.Options = fd.builder.optionsUnmarshaler(descopts.File, rawOptions)
 }
 
-func (ed *Enum) unmarshalFull(b []byte, nb *nameBuilder) {
+func (ed *Enum) unmarshalFull(b []byte, sb *strs.Builder) {
 	var rawValues [][]byte
 	var rawOptions []byte
 	if !ed.L1.eagerValues {
@@ -202,7 +203,7 @@
 			case fieldnum.EnumDescriptorProto_Value:
 				rawValues = append(rawValues, v)
 			case fieldnum.EnumDescriptorProto_ReservedName:
-				ed.L2.ReservedNames.List = append(ed.L2.ReservedNames.List, pref.Name(nb.MakeString(v)))
+				ed.L2.ReservedNames.List = append(ed.L2.ReservedNames.List, pref.Name(sb.MakeString(v)))
 			case fieldnum.EnumDescriptorProto_ReservedRange:
 				ed.L2.ReservedRanges.List = append(ed.L2.ReservedRanges.List, unmarshalEnumReservedRange(v))
 			case fieldnum.EnumDescriptorProto_Options:
@@ -216,7 +217,7 @@
 	if !ed.L1.eagerValues && len(rawValues) > 0 {
 		ed.L2.Values.List = make([]EnumValue, len(rawValues))
 		for i, b := range rawValues {
-			ed.L2.Values.List[i].unmarshalFull(b, nb, ed.L0.ParentFile, ed, i)
+			ed.L2.Values.List[i].unmarshalFull(b, sb, ed.L0.ParentFile, ed, i)
 		}
 	}
 	ed.L2.Options = ed.L0.ParentFile.builder.optionsUnmarshaler(descopts.Enum, rawOptions)
@@ -244,7 +245,7 @@
 	return r
 }
 
-func (vd *EnumValue) unmarshalFull(b []byte, nb *nameBuilder, pf *File, pd pref.Descriptor, i int) {
+func (vd *EnumValue) unmarshalFull(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
 	vd.L0.ParentFile = pf
 	vd.L0.Parent = pd
 	vd.L0.Index = i
@@ -267,7 +268,7 @@
 			switch num {
 			case fieldnum.EnumValueDescriptorProto_Name:
 				// NOTE: Enum values are in the same scope as the enum parent.
-				vd.L0.FullName = nb.AppendFullName(pd.Parent().FullName(), v)
+				vd.L0.FullName = appendFullName(sb, pd.Parent().FullName(), v)
 			case fieldnum.EnumValueDescriptorProto_Options:
 				rawOptions = appendOptions(rawOptions, v)
 			}
@@ -279,7 +280,7 @@
 	vd.L1.Options = pf.builder.optionsUnmarshaler(descopts.EnumValue, rawOptions)
 }
 
-func (md *Message) unmarshalFull(b []byte, nb *nameBuilder) {
+func (md *Message) unmarshalFull(b []byte, sb *strs.Builder) {
 	var rawFields, rawOneofs [][]byte
 	var enumIdx, messageIdx, extensionIdx int
 	var rawOptions []byte
@@ -297,7 +298,7 @@
 			case fieldnum.DescriptorProto_OneofDecl:
 				rawOneofs = append(rawOneofs, v)
 			case fieldnum.DescriptorProto_ReservedName:
-				md.L2.ReservedNames.List = append(md.L2.ReservedNames.List, pref.Name(nb.MakeString(v)))
+				md.L2.ReservedNames.List = append(md.L2.ReservedNames.List, pref.Name(sb.MakeString(v)))
 			case fieldnum.DescriptorProto_ReservedRange:
 				md.L2.ReservedRanges.List = append(md.L2.ReservedRanges.List, unmarshalMessageReservedRange(v))
 			case fieldnum.DescriptorProto_ExtensionRange:
@@ -306,13 +307,13 @@
 				md.L2.ExtensionRanges.List = append(md.L2.ExtensionRanges.List, r)
 				md.L2.ExtensionRangeOptions = append(md.L2.ExtensionRangeOptions, opts)
 			case fieldnum.DescriptorProto_EnumType:
-				md.L1.Enums.List[enumIdx].unmarshalFull(v, nb)
+				md.L1.Enums.List[enumIdx].unmarshalFull(v, sb)
 				enumIdx++
 			case fieldnum.DescriptorProto_NestedType:
-				md.L1.Messages.List[messageIdx].unmarshalFull(v, nb)
+				md.L1.Messages.List[messageIdx].unmarshalFull(v, sb)
 				messageIdx++
 			case fieldnum.DescriptorProto_Extension:
-				md.L1.Extensions.List[extensionIdx].unmarshalFull(v, nb)
+				md.L1.Extensions.List[extensionIdx].unmarshalFull(v, sb)
 				extensionIdx++
 			case fieldnum.DescriptorProto_Options:
 				md.unmarshalOptions(v)
@@ -328,14 +329,14 @@
 		md.L2.Oneofs.List = make([]Oneof, len(rawOneofs))
 		for i, b := range rawFields {
 			fd := &md.L2.Fields.List[i]
-			fd.unmarshalFull(b, nb, md.L0.ParentFile, md, i)
+			fd.unmarshalFull(b, sb, md.L0.ParentFile, md, i)
 			if fd.L1.Cardinality == pref.Required {
 				md.L2.RequiredNumbers.List = append(md.L2.RequiredNumbers.List, fd.L1.Number)
 			}
 		}
 		for i, b := range rawOneofs {
 			od := &md.L2.Oneofs.List[i]
-			od.unmarshalFull(b, nb, md.L0.ParentFile, md, i)
+			od.unmarshalFull(b, sb, md.L0.ParentFile, md, i)
 		}
 	}
 	md.L2.Options = md.L0.ParentFile.builder.optionsUnmarshaler(descopts.Message, rawOptions)
@@ -413,7 +414,7 @@
 	return r, rawOptions
 }
 
-func (fd *Field) unmarshalFull(b []byte, nb *nameBuilder, pf *File, pd pref.Descriptor, i int) {
+func (fd *Field) unmarshalFull(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
 	fd.L0.ParentFile = pf
 	fd.L0.Parent = pd
 	fd.L0.Index = i
@@ -450,9 +451,9 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.FieldDescriptorProto_Name:
-				fd.L0.FullName = nb.AppendFullName(pd.FullName(), v)
+				fd.L0.FullName = appendFullName(sb, pd.FullName(), v)
 			case fieldnum.FieldDescriptorProto_JsonName:
-				fd.L1.JSONName = JSONName(nb.MakeString(v))
+				fd.L1.JSONName = JSONName(sb.MakeString(v))
 			case fieldnum.FieldDescriptorProto_DefaultValue:
 				fd.L1.Default.val = pref.ValueOf(v) // temporarily store as bytes; later resolved in resolveMessages
 			case fieldnum.FieldDescriptorProto_TypeName:
@@ -467,7 +468,7 @@
 		}
 	}
 	if rawTypeName != nil {
-		name := nb.MakeFullName(rawTypeName)
+		name := makeFullName(sb, rawTypeName)
 		switch fd.L1.Kind {
 		case pref.EnumKind:
 			fd.L1.Enum = PlaceholderEnum(name)
@@ -500,7 +501,7 @@
 	}
 }
 
-func (od *Oneof) unmarshalFull(b []byte, nb *nameBuilder, pf *File, pd pref.Descriptor, i int) {
+func (od *Oneof) unmarshalFull(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
 	od.L0.ParentFile = pf
 	od.L0.Parent = pd
 	od.L0.Index = i
@@ -515,7 +516,7 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.OneofDescriptorProto_Name:
-				od.L0.FullName = nb.AppendFullName(pd.FullName(), v)
+				od.L0.FullName = appendFullName(sb, pd.FullName(), v)
 			case fieldnum.OneofDescriptorProto_Options:
 				rawOptions = appendOptions(rawOptions, v)
 			}
@@ -527,7 +528,7 @@
 	od.L1.Options = pf.builder.optionsUnmarshaler(descopts.Oneof, rawOptions)
 }
 
-func (xd *Extension) unmarshalFull(b []byte, nb *nameBuilder) {
+func (xd *Extension) unmarshalFull(b []byte, sb *strs.Builder) {
 	var rawTypeName []byte
 	var rawOptions []byte
 	xd.L2 = new(ExtensionL2)
@@ -547,7 +548,7 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.FieldDescriptorProto_JsonName:
-				xd.L2.JSONName = JSONName(nb.MakeString(v))
+				xd.L2.JSONName = JSONName(sb.MakeString(v))
 			case fieldnum.FieldDescriptorProto_DefaultValue:
 				xd.L2.Default.val = pref.ValueOf(v) // temporarily store as bytes; later resolved in resolveExtensions
 			case fieldnum.FieldDescriptorProto_TypeName:
@@ -562,7 +563,7 @@
 		}
 	}
 	if rawTypeName != nil {
-		name := nb.MakeFullName(rawTypeName)
+		name := makeFullName(sb, rawTypeName)
 		switch xd.L1.Kind {
 		case pref.EnumKind:
 			xd.L2.Enum = PlaceholderEnum(name)
@@ -592,7 +593,7 @@
 	}
 }
 
-func (sd *Service) unmarshalFull(b []byte, nb *nameBuilder) {
+func (sd *Service) unmarshalFull(b []byte, sb *strs.Builder) {
 	var rawMethods [][]byte
 	var rawOptions []byte
 	sd.L2 = new(ServiceL2)
@@ -617,13 +618,13 @@
 	if len(rawMethods) > 0 {
 		sd.L2.Methods.List = make([]Method, len(rawMethods))
 		for i, b := range rawMethods {
-			sd.L2.Methods.List[i].unmarshalFull(b, nb, sd.L0.ParentFile, sd, i)
+			sd.L2.Methods.List[i].unmarshalFull(b, sb, sd.L0.ParentFile, sd, i)
 		}
 	}
 	sd.L2.Options = sd.L0.ParentFile.builder.optionsUnmarshaler(descopts.Service, rawOptions)
 }
 
-func (md *Method) unmarshalFull(b []byte, nb *nameBuilder, pf *File, pd pref.Descriptor, i int) {
+func (md *Method) unmarshalFull(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
 	md.L0.ParentFile = pf
 	md.L0.Parent = pd
 	md.L0.Index = i
@@ -647,11 +648,11 @@
 			b = b[m:]
 			switch num {
 			case fieldnum.MethodDescriptorProto_Name:
-				md.L0.FullName = nb.AppendFullName(pd.FullName(), v)
+				md.L0.FullName = appendFullName(sb, pd.FullName(), v)
 			case fieldnum.MethodDescriptorProto_InputType:
-				md.L1.Input = PlaceholderMessage(nb.MakeFullName(v))
+				md.L1.Input = PlaceholderMessage(makeFullName(sb, v))
 			case fieldnum.MethodDescriptorProto_OutputType:
-				md.L1.Output = PlaceholderMessage(nb.MakeFullName(v))
+				md.L1.Output = PlaceholderMessage(makeFullName(sb, v))
 			case fieldnum.MethodDescriptorProto_Options:
 				rawOptions = appendOptions(rawOptions, v)
 			}
diff --git a/internal/filedesc/name_pure.go b/internal/filedesc/name_pure.go
deleted file mode 100644
index 5626829..0000000
--- a/internal/filedesc/name_pure.go
+++ /dev/null
@@ -1,34 +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.
-
-// +build purego appengine
-
-package filedesc
-
-import pref "google.golang.org/protobuf/reflect/protoreflect"
-
-func getNameBuilder() *nameBuilder { return nil }
-func putNameBuilder(*nameBuilder)  {}
-
-type nameBuilder struct{}
-
-// MakeFullName converts b to a protoreflect.FullName,
-// where b must start with a leading dot.
-func (*nameBuilder) MakeFullName(b []byte) pref.FullName {
-	if len(b) == 0 || b[0] != '.' {
-		panic("name reference must be fully qualified")
-	}
-	return pref.FullName(b[1:])
-}
-
-// AppendFullName is equivalent to protoreflect.FullName.Append.
-func (*nameBuilder) AppendFullName(prefix pref.FullName, name []byte) pref.FullName {
-	return prefix.Append(pref.Name(name))
-}
-
-// MakeString is equivalent to string(b), but optimized for large batches
-// with a shared lifetime.
-func (*nameBuilder) MakeString(b []byte) string {
-	return string(b)
-}
diff --git a/internal/filedesc/name_unsafe.go b/internal/filedesc/name_unsafe.go
deleted file mode 100644
index 317114f..0000000
--- a/internal/filedesc/name_unsafe.go
+++ /dev/null
@@ -1,124 +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.
-
-// +build !purego,!appengine
-
-package filedesc
-
-import (
-	"sync"
-	"unsafe"
-
-	pref "google.golang.org/protobuf/reflect/protoreflect"
-)
-
-var nameBuilderPool = sync.Pool{
-	New: func() interface{} { return new(nameBuilder) },
-}
-
-func getNameBuilder() *nameBuilder {
-	return nameBuilderPool.Get().(*nameBuilder)
-}
-func putNameBuilder(b *nameBuilder) {
-	nameBuilderPool.Put(b)
-}
-
-type nameBuilder struct {
-	sb stringBuilder
-}
-
-// MakeFullName converts b to a protoreflect.FullName,
-// where b must start with a leading dot.
-func (nb *nameBuilder) MakeFullName(b []byte) pref.FullName {
-	if len(b) == 0 || b[0] != '.' {
-		panic("name reference must be fully qualified")
-	}
-	return pref.FullName(nb.MakeString(b[1:]))
-}
-
-// AppendFullName is equivalent to protoreflect.FullName.Append,
-// but optimized for large batches where each name has a shared lifetime.
-func (nb *nameBuilder) AppendFullName(prefix pref.FullName, name []byte) pref.FullName {
-	n := len(prefix) + len(".") + len(name)
-	if len(prefix) == 0 {
-		n -= len(".")
-	}
-	nb.grow(n)
-	nb.sb.WriteString(string(prefix))
-	nb.sb.WriteByte('.')
-	nb.sb.Write(name)
-	return pref.FullName(nb.last(n))
-}
-
-// MakeString is equivalent to string(b), but optimized for large batches
-// with a shared lifetime.
-func (nb *nameBuilder) MakeString(b []byte) string {
-	nb.grow(len(b))
-	nb.sb.Write(b)
-	return nb.last(len(b))
-}
-
-func (nb *nameBuilder) last(n int) string {
-	s := nb.sb.String()
-	return s[len(s)-n:]
-}
-
-func (nb *nameBuilder) grow(n int) {
-	const batchSize = 1 << 16
-	if nb.sb.Cap()-nb.sb.Len() < n {
-		nb.sb.Reset()
-		nb.sb.Grow(batchSize)
-	}
-}
-
-// stringsBuilder is a simplified copy of the strings.Builder from Go1.12:
-//	* removed the shallow copy check
-//	* removed methods that we do not use (e.g. WriteRune)
-//
-// A forked version is used:
-//	* to enable Go1.9 support, but strings.Builder was added in Go1.10
-//	* for the Cap method, which was missing until Go1.12
-//
-// TODO: Remove this when Go1.12 is the minimally supported toolchain version.
-type stringBuilder struct {
-	buf []byte
-}
-
-func (b *stringBuilder) String() string {
-	return *(*string)(unsafe.Pointer(&b.buf))
-}
-func (b *stringBuilder) Len() int {
-	return len(b.buf)
-}
-func (b *stringBuilder) Cap() int {
-	return cap(b.buf)
-}
-func (b *stringBuilder) Reset() {
-	b.buf = nil
-}
-func (b *stringBuilder) grow(n int) {
-	buf := make([]byte, len(b.buf), 2*cap(b.buf)+n)
-	copy(buf, b.buf)
-	b.buf = buf
-}
-func (b *stringBuilder) Grow(n int) {
-	if n < 0 {
-		panic("stringBuilder.Grow: negative count")
-	}
-	if cap(b.buf)-len(b.buf) < n {
-		b.grow(n)
-	}
-}
-func (b *stringBuilder) Write(p []byte) (int, error) {
-	b.buf = append(b.buf, p...)
-	return len(p), nil
-}
-func (b *stringBuilder) WriteByte(c byte) error {
-	b.buf = append(b.buf, c)
-	return nil
-}
-func (b *stringBuilder) WriteString(s string) (int, error) {
-	b.buf = append(b.buf, s...)
-	return len(s), nil
-}