Generated Java code causes "redundant cast to Builder" warnings

[slovdahl]

What version of protobuf and what language are you using?
Version: v3.6.1
Gradle plugin version: v0.8.6
Language: Java

What operating system (Linux, Windows, ...) and version?
Ubuntu 16.04

What runtime / compiler are you using (e.g., python version or gcc version)

$ java -version
openjdk version "1.8.0_181"
OpenJDK Runtime Environment (build 1.8.0_181-8u181-b13-0ubuntu0.16.04.1-b13)
OpenJDK 64-Bit Server VM (build 25.181-b13, mixed mode)

What did you do?

I don't know if this is a regression or always has been like this, this is the first time I'm using the protobuf java stuff.

I prepared a project demonstrating the issue https://github.com/slovdahl/protobuf-java-warnings, but in short:

1. Created a gradle project:

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.6'
    }
}

repositories {
    mavenCentral()
}

apply plugin: 'java'
apply plugin: 'com.google.protobuf'

protobuf {
    protoc {
        artifact = 'com.google.protobuf:protoc:3.6.1'
    }
}

dependencies {
    compile 'com.google.protobuf:protobuf-java:3.6.1'
}

compileJava {
    options.compilerArgs += ['-Xlint']
}

2. Created a proto definition:

syntax = "proto3";

package com.foo.bar.proto;

option java_outer_classname = "Event";

message Foo {
    int32 id = 1;
}

3. Executed ./gradlew compileJava, which generates the java code and compiles the generated code.

What did you expect to see
No java compiler warnings.

What did you see instead?

/home/dev/protobuf-test/build/generated/source/proto/main/java/com/foo/bar/proto/Event.java:341: warning: [cast] redundant cast to Builder
        return (Builder) super.clone();
               ^
/home/dev/protobuf-test/build/generated/source/proto/main/java/com/foo/bar/proto/Event.java:347: warning: [cast] redundant cast to Builder
        return (Builder) super.setField(field, value);
               ^
/home/dev/protobuf-test/build/generated/source/proto/main/java/com/foo/bar/proto/Event.java:352: warning: [cast] redundant cast to Builder
        return (Builder) super.clearField(field);
               ^
/home/dev/protobuf-test/build/generated/source/proto/main/java/com/foo/bar/proto/Event.java:357: warning: [cast] redundant cast to Builder
        return (Builder) super.clearOneof(oneof);
               ^
/home/dev/protobuf-test/build/generated/source/proto/main/java/com/foo/bar/proto/Event.java:363: warning: [cast] redundant cast to Builder
        return (Builder) super.setRepeatedField(field, index, value);
               ^
/home/dev/protobuf-test/build/generated/source/proto/main/java/com/foo/bar/proto/Event.java:369: warning: [cast] redundant cast to Builder
        return (Builder) super.addRepeatedField(field, value);
               ^
6 warnings

[slovdahl]

Would you be willing to accept a pull request that fixes this?

[slovdahl]

Thanks for accepting the fix!

@BSBandme What's your policy regarding new releases, how often are releases made? Not asking that you make a release immediately, just want to know how to set my expectations 🙂

[terje2001]

Thanks for fixing this!

@BSBandme : I second @slovdahl request, the javac output is disruptive and noisy in our process. If a new release is not imminent, would it be possible to backport to the 3.6.x branch and get a release of that?

[perlun]

@acozzette You seem to have tagged a 3.6.1.1 release 7 days ago, but this version is not yet available in Maven Central from what I can tell: https://search.maven.org/search?q=g:com.google.protobuf

Also, this commit (dc81f79) doesn't seem to be present on the 3.6.x branch for now: v3.6.1...3.6.x, so I'm pretty certain it isn't included in the version that got tagged as 3.6.1.1.

If you could cherry-pick this change (or, make someone else do it) and put out a 3.6.1.2 or 3.6.2 version, me (and others) would be incredibly thankful. Thanks in advance! 👍

[acozzette]

@perlun That 3.6.1.1 release was just meant to include an important fix that was blocking the Bazel 0.20 release, so I tagged a commit without doing a full release and publishing artifacts and everything. We are going to do a real 3.7 release soon, so that will include all the changes that are currently on master.

[perlun]

@acozzette Wonderful, thanks for the update. 👍

[luster]

any update on the timeline for new release?

[perlun]

Ping @acozzette or others - any updates? (I was reminded about this now since it floods our build output)

[klaraward]

Another ping, any ETA for the next release?

[acozzette]

We are working on it now. I think it's probably ready to go but we're going to do another rc release just to be safe before we release 3.7.0.

[voidzcy]

Seems this issue is still not fixed in javalite generated code. I saw those warnings when using protobuf-javalite:3.11.0.

[bmarwell]

please reopen as requested in #8208 by @perezd in #8208 (comment).

[perezd]

Oops, didn't realize it was closed.

[bmarwell]

Hi, any progress on this?

[perezd]

Has this been reproduced w/ our latest java release? (3.17)

[bmarwell]

Huh, maybe you could add a test. PR #5247 sadly did not add any.

[danadam]

The script in attachment, with protoc, protobuf-java-3.19.4.jar and protobuf-javalite-3.19.4.jar in current directory, gives output:

javac 11.0.13
libprotoc 3.19.4
test proto2 full
test proto3 full
test proto2 lite
java-test/TestProto2.java:147: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
1 warning
test proto3 lite
java-test/TestProto3.java:133: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
1 warning

redundant.cast.sh.txt

[perezd]

We'll accept PRs to resolve this similar to the others if you'd like.

[bmarwell]

We'll accept PRs to resolve this similar to the others if you'd like.

You already did this for non-lite versions:
dc81f79

[perezd]

Great! That'll make it easier for someone to send us a PR, appreciate it!