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// 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 fieldsort defines an ordering of fields.
// The ordering defined by this package matches the historic behavior of the proto
// package, placing extensions first and oneofs last.
// There is no guarantee about stability of the wire encoding, and users should not
// depend on the order defined in this package as it is subject to change without
// notice.
package fieldsort
import (
// Less returns true if field a comes before field j in ordered wire marshal output.
func Less(a, b protoreflect.FieldDescriptor) bool {
ea := a.IsExtension()
eb := b.IsExtension()
oa := a.ContainingOneof()
ob := b.ContainingOneof()
switch {
case ea != eb:
return ea
case oa != nil && ob != nil:
if oa == ob {
return a.Number() < b.Number()
return oa.Index() < ob.Index()
case oa != nil:
return false
case ob != nil:
return true
return a.Number() < b.Number()