compiler serial warnings when compiling generated source with Java 18 #9673
Description
What version of protobuf and what language are you using?
Version: 3.20.0-rc-1
Language: Java
What operating system (Linux, Windows, ...) and version?
macOS 12.3
What runtime / compiler are you using (e.g., python version or gcc version)
using com.google.protobuf:protoc:3.20.0-rc-1:exe:osx-x86_64 compiler artifact
invoked via org.xolstice.maven.plugins:protobuf-maven-plugin:0.6.1
% java -version
openjdk version "18" 2022-03-22
OpenJDK Runtime Environment (build 18+36-2087)
OpenJDK 64-Bit Server VM (build 18+36-2087, mixed mode, sharing)
What did you do?
Compile the code generated from the following proto definition:
example.proto
syntax = "proto3";
package test;
option java_package = "org.example.test";
option java_outer_classname = "TestProto";
option java_multiple_files = true;
message KeyValuePair {
string key = 1;
string value = 2;
}
What did you expect to see
No compiler warnings when compiling the generated Java source code.
What did you see instead?
As part of https://bugs.openjdk.java.net/browse/JDK-8274336 https://bugs.openjdk.java.net/browse/JDK-8274335 Java 18 added additional linter checks.
Java 18 reports the following warning for generated source files, and fails compilation if -Werror is specified:
KeyValuePair.java:[19,4] [serial] non-transient instance field of a serializable class declared with a non-serializable type
See KeyValuePair.java.txt for the generated source
Anything else we should know about your project / environment
Today possible workarounds are to either:
a) not pass -Werror to the Java compiler
b) mangle the source code generated by protoc using something like the maven-replacer-plugin, to add the necessary @SuppressWarnings annotations, which is rather ugly and brittle
e.g.
<plugin>
<groupId>com.google.code.maven-replacer-plugin</groupId>
<artifactId>maven-replacer-plugin</artifactId>
<executions>
<execution>
<phase>generate-sources</phase>
<goals>
<goal>replace</goal>
</goals>
</execution>
</executions>
<configuration>
<includes>
<include>target/generated-sources/**/*.java</include>
</includes>
<regex>true</regex>
<regexFlags>
<regexFlag>MULTILINE</regexFlag>
</regexFlags>
<replacements>
<replacement>
<token>public final class</token>
<value>@SuppressWarnings("serial") public final class</value>
</replacement>
</replacements>
</configuration>
</plugin>