Deprecated field PARSER is accessed in generated code

[adorokhine]

What version of protobuf and what language are you using?
Version: 3.11.4
Language: Java

What operating system (Linux, Windows, ...) and version?
Linux 4.15.0-74-generic
What runtime / compiler are you using (e.g., python version or gcc version)
Java 1.8.0_232

What did you do?
Steps to reproduce the behavior:

1. Configure gradle to treat warnings as errors:

tasks.withType(JavaCompile) {
  options.compilerArgs << "-Xlint:all" << "-Werror"
}

2. Try to compile a protobuf
3. Build fails on this generated code:

    @java.lang.Deprecated public static final com.google.protobuf.Parser<PbStat>
        PARSER = new com.google.protobuf.AbstractParser<PbStat>() {
      @java.lang.Override
      public PbStat parsePartialFrom(
          com.google.protobuf.CodedInputStream input,
          com.google.protobuf.ExtensionRegistryLite extensionRegistry)
          throws com.google.protobuf.InvalidProtocolBufferException {
        return new PbStat(input, extensionRegistry);
      }
    };

Error: warning: [deprecation] PARSER in PbStat has been deprecated stat_ = input.readMessage(com.dorokhine.ufs.proto.Inode.PbStat.PARSER, extensionRegistry);

The access to the deprecated field is in the private message constructor, in switch(tag):

    case 10: {
              com.example.Message.PbStat.Builder subBuilder = null;
              if (((bitField0_ & 0x00000002) != 0)) {
                subBuilder = stat_.toBuilder();
              }
              stat_ = input.readMessage(com.example.Message.PbStat.PARSER, extensionRegistry);
              if (subBuilder != null) {
                subBuilder.mergeFrom(stat_);
                stat_ = subBuilder.buildPartial();
              }
              bitField0_ |= 0x00000002;
              break;
            }

What did you expect to see
Protobuf compiles without warnings

What did you see instead?
Build fails

Make sure you include information that can help us debug (full error message, exception listing, stack trace, logs).

Anything else we should know about your project / environment

[oehme]

This is still an issue as of 3.19.3.

[chasebradford]

This appears to be caused by this change, and is specific to java code generated from syntax2 files.
cc5a1bf

That change makes the PARSER field deprecated, but generated methods use it anyway, leading to the warning. Perhaps a private method that ignores the deprecation warning could return this field and other generated methods can be changed to reference the non-deprecated method instead.

[googleberg]

Consider a breaking change in the Java API in a future release to make this static object private.

[github-actions]

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