com.google.protobuf.GeneratedMessageV3.isStringEmpty should be public

[ochinchina]

Version: v3.19.1
Language: Java
OS: Windows 10

When compiling the protoc 3.19.1 generated java source codes from a .proto file, following error is raised:

 error: cannot find symbol
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(appId_)) {
                                               ^
  symbol:   method isStringEmpty(Object)
  location: class GeneratedMessageV3

After checking the source code of the java class com.google.protobuf.GeneratedMessageV3 and found the method isStringEmpty is defined as protected instead of public.

[elharo]

What file is the error found in? Do you have the complete source code of that file handy?

[ochinchina]

detailed steps for re-produce this bug:

1. download the protoc v3.19.1 from https://github.com/protocolbuffers/protobuf/releases/download/v3.19.1/protoc-3.19.1-linux-x86_64.zip

$ wget https://github.com/protocolbuffers/protobuf/releases/download/v3.19.1/protoc-3.19.1-linux-x86_64.zip

2. unzip the downloaded protoc

$ unzip protoc-3.19.1-linux-x86_64.zip
$ cd protoc-3.19.1

3. compile the following helloworld.proto

syntax = "proto3";

option java_multiple_files = true;
option java_package = "io.grpc.examples.helloworld";
option java_outer_classname = "HelloWorldProto";
option objc_class_prefix = "HLW";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

with command:

$ mkdir java_output
$ bin/protoc --java_output=java_output helloworld.proto

go to the directory java_output/io/grpc/examples/helloworld and grep the com.google.protobuf.GeneratedMessageV3.isStringEmpty

$ cd java_output/io/grpc/examples/helloworld
$ grep com.google.protobuf.GeneratedMessageV3.isStringEmpty *.java
HelloReply.java:    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(message_)) {
HelloReply.java:    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(message_)) {
HelloRequest.java:    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(name_)) {
HelloRequest.java:    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(name_)) {

The protected method isStringEmpty in class com.google.protobuf.GeneratedMessageV3 is used by class HelloReply and HelloRequest. When trying to compile the above generated source code, we get the error:

 error: cannot find symbol
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(appId_)) {
                                               ^
  symbol:   method isStringEmpty(Object)
  location: class GeneratedMessageV3

[perezd]

Can you confirm you're using the newest runtime when compiling the source code produced by that version of protoc? I think we've seen a similar issue in the past.

[toffentoffen]

I've experienced a similar issue will trying to use the latest version of protoc, protbuf-java and grpc-java to being able to compile the protos in a Mac M1 trough the protobuf maven plugin.

com.google.protobuf.protoc = 3.19.1
protoc-gen-grpc-java.plugin = 1.42.1 (has an internal dependency on protobuf-java = 3.17.2) (does not contain com.google.protobuf.GeneratedMessageV3.isStringEmpty)
protobuf-java = 3.19.1
protobuf-java-util = 3.19.1

The problem is that the latest protoc generates code that depends on function (com.google.protobuf.GeneratedMessageV3.isStringEmpty) that are available from 3.17.3+.

So, as @perezd said, probably your compiling agains an older version of protobuf-java.

So a workaround would be using protoc 3.17.3 as I've mentioned #8062 (comment) and grpc/grpc-java#8724 (where if also asked to upgrade to the latest protobuf 3.19.1 release)