Source: legacy_enum.go in package google.golang.org/protobuf/internal/impl


package impl

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

	"google.golang.org/protobuf/internal/filedesc"
	"google.golang.org/protobuf/internal/strs"
	"google.golang.org/protobuf/reflect/protoreflect"
	pref "google.golang.org/protobuf/reflect/protoreflect"
)

legacyEnumName returns the name of enums used in legacy code. It is neither the protobuf full name nor the qualified Go name, but rather an odd hybrid of both.

func legacyEnumName(ed pref.EnumDescriptor) string {
	var protoPkg string
	enumName := string(ed.FullName())
	if fd := ed.ParentFile(); fd != nil {
		protoPkg = string(fd.Package())
		enumName = strings.TrimPrefix(enumName, protoPkg+".")
	}
	if protoPkg == "" {
		return strs.GoCamelCase(enumName)
	}
	return protoPkg + "." + strs.GoCamelCase(enumName)
}

legacyWrapEnum wraps v as a protoreflect.Enum, where v must be a int32 kind and not implement the v2 API already.

func legacyWrapEnum(v reflect.Value) pref.Enum {
	et := legacyLoadEnumType(v.Type())
	return et.New(pref.EnumNumber(v.Int()))
}

var legacyEnumTypeCache sync.Map // map[reflect.Type]protoreflect.EnumType

legacyLoadEnumType dynamically loads a protoreflect.EnumType for t, where t must be an int32 kind and not implement the v2 API already.

Fast-path: check if a EnumType is cached for this concrete type.

	if et, ok := legacyEnumTypeCache.Load(t); ok {
		return et.(pref.EnumType)
	}

Slow-path: derive enum descriptor and initialize EnumType.

	var et pref.EnumType
	ed := LegacyLoadEnumDesc(t)
	et = &legacyEnumType{
		desc:   ed,
		goType: t,
	}
	if et, ok := legacyEnumTypeCache.LoadOrStore(t, et); ok {
		return et.(pref.EnumType)
	}
	return et
}

type legacyEnumType struct {
	desc   pref.EnumDescriptor
	goType reflect.Type
	m      sync.Map // map[protoreflect.EnumNumber]proto.Enum
}

func (t *legacyEnumType) New(n pref.EnumNumber) pref.Enum {
	if e, ok := t.m.Load(n); ok {
		return e.(pref.Enum)
	}
	e := &legacyEnumWrapper{num: n, pbTyp: t, goTyp: t.goType}
	t.m.Store(n, e)
	return e
}
func (t *legacyEnumType) Descriptor() pref.EnumDescriptor {
	return t.desc
}

type legacyEnumWrapper struct {
	num   pref.EnumNumber
	pbTyp pref.EnumType
	goTyp reflect.Type
}

func (e *legacyEnumWrapper) Descriptor() pref.EnumDescriptor {
	return e.pbTyp.Descriptor()
}
func (e *legacyEnumWrapper) Type() pref.EnumType {
	return e.pbTyp
}
func (e *legacyEnumWrapper) Number() pref.EnumNumber {
	return e.num
}
func (e *legacyEnumWrapper) ProtoReflect() pref.Enum {
	return e
}
func (e *legacyEnumWrapper) protoUnwrap() interface{} {
	v := reflect.New(e.goTyp).Elem()
	v.SetInt(int64(e.num))
	return v.Interface()
}

var (
	_ pref.Enum = (*legacyEnumWrapper)(nil)
	_ unwrapper = (*legacyEnumWrapper)(nil)
)

var legacyEnumDescCache sync.Map // map[reflect.Type]protoreflect.EnumDescriptor

LegacyLoadEnumDesc returns an EnumDescriptor derived from the Go type, which must be an int32 kind and not implement the v2 API already. This is exported for testing purposes.

Fast-path: check if an EnumDescriptor is cached for this concrete type.

	if ed, ok := legacyEnumDescCache.Load(t); ok {
		return ed.(pref.EnumDescriptor)
	}

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))
	}
	edV1, ok := ev.(enumV1)
	if !ok {
		return aberrantLoadEnumDesc(t)
	}
	b, idxs := edV1.EnumDescriptor()

	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.(protoreflect.EnumDescriptor)
	}
	return ed
}

var aberrantEnumDescCache sync.Map // map[reflect.Type]protoreflect.EnumDescriptor

aberrantLoadEnumDesc returns an EnumDescriptor derived from the Go type, which must not implement protoreflect.Enum or enumV1. 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 protobuf full name, which we also do not know. Thus, this produces some bogus enum descriptor based on the Go type name.

Fast-path: check if an EnumDescriptor is cached for this concrete type.

	if ed, ok := aberrantEnumDescCache.Load(t); ok {
		return ed.(pref.EnumDescriptor)
	}

Slow-path: construct a bogus, but unique EnumDescriptor.

	ed := &filedesc.Enum{L2: new(filedesc.EnumL2)}
	ed.L0.FullName = AberrantDeriveFullName(t) // e.g., github_com.user.repo.MyEnum
	ed.L0.ParentFile = filedesc.SurrogateProto3
	ed.L2.Values.List = append(ed.L2.Values.List, filedesc.EnumValue{})

TODO: Use the presence of a UnmarshalJSON method to determine proto2?


	vd := &ed.L2.Values.List[0]
	vd.L0.FullName = ed.L0.FullName + "_UNKNOWN" // e.g., github_com.user.repo.MyEnum_UNKNOWN
	vd.L0.ParentFile = ed.L0.ParentFile
	vd.L0.Parent = ed

TODO: We could use the String method to obtain some enum value names by starting at 0 and print the enum until it produces invalid identifiers. An exhaustive query is clearly impractical, but can be best-effort.


	if ed, ok := aberrantEnumDescCache.LoadOrStore(t, ed); ok {
		return ed.(pref.EnumDescriptor)
	}
	return ed
}

AberrantDeriveFullName 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. This is exported for testing purposes.

func AberrantDeriveFullName(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, "."))