Inconsistency of Protobuf Marshal

.gitignore

/example/example.pb.go

README.md

Hello

example.proto

syntax = "proto3";

option go_package = "biawak/example";

message Message {
  bytes text = 1;
  repeated string biawaks = 2;
}

gen.sh

protoc --go_out=..  example.proto

go.mod

module biawak

go 1.19

require (
	github.com/golang/protobuf v1.5.3
	google.golang.org/protobuf v1.30.0
)

go.sum

github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
github.com/golang/protobuf v1.5.3 h1:KhyjKVUg7Usr/dYsdSqoFveMYd5ko72D+zANwlG1mmg=
github.com/golang/protobuf v1.5.3/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
google.golang.org/protobuf v1.30.0 h1:kPPoIgf3TsEvrm0PFe15JQ+570QVxYzEvvHqChK+cng=
google.golang.org/protobuf v1.30.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=

main.go

package main

import (
	fmt "fmt"

	"biawak/example"

	"github.com/golang/protobuf/proto"
)

func main() {
	var text = []byte("hello")
	message := &example.Message{
		Text:    text,
		Biawaks: make([]string, 0, 100),
	}

	fmt.Println("BEFORE:", message.Biawaks == nil, cap(message.Biawaks))

	data, err := proto.Marshal(message)
	if err != nil {
		panic(err)
	}

	// fmt.Println(data) // [10 5 104 101 108 108 111]

	newMessage := &example.Message{}
	err = proto.Unmarshal(data, newMessage)
	if err != nil {
		panic(err)
	}

	fmt.Println("AFTER:", newMessage.Biawaks == nil, cap(newMessage.Biawaks))

	// fmt.Println(newMessage.GetText()) // [104 101 108 108 111]
}

out.txt

BEFORE: false 100
AFTER: true 0

run.sh

go run main.go > out.txt