presence.go raw

   1  // Copyright 2025 The Go Authors. All rights reserved.
   2  // Use of this source code is governed by a BSD-style
   3  // license that can be found in the LICENSE file.
   4  
   5  package filedesc
   6  
   7  import "google.golang.org/protobuf/reflect/protoreflect"
   8  
   9  // UsePresenceForField reports whether the presence bitmap should be used for
  10  // the specified field.
  11  func UsePresenceForField(fd protoreflect.FieldDescriptor) (usePresence, canBeLazy bool) {
  12  	switch {
  13  	case fd.ContainingOneof() != nil && !fd.ContainingOneof().IsSynthetic():
  14  		// Oneof fields never use the presence bitmap.
  15  		//
  16  		// Synthetic oneofs are an exception: Those are used to implement proto3
  17  		// optional fields and hence should follow non-oneof field semantics.
  18  		return false, false
  19  
  20  	case fd.IsMap():
  21  		// Map-typed fields never use the presence bitmap.
  22  		return false, false
  23  
  24  	case fd.Kind() == protoreflect.MessageKind || fd.Kind() == protoreflect.GroupKind:
  25  		// Lazy fields always use the presence bitmap (only messages can be lazy).
  26  		isLazy := fd.(interface{ IsLazy() bool }).IsLazy()
  27  		return isLazy, isLazy
  28  
  29  	default:
  30  		// If the field has presence, use the presence bitmap.
  31  		return fd.HasPresence(), false
  32  	}
  33  }
  34