UnusedVariable and MethodCanBeStatic should whitelist serialization methods

[PhilippWendler]

In Error-Prone 2.3.3, the following class triggers warnings:

public class Test {
  private void writeObject(java.io.ObjectOutputStream stream) throws IOException {}

  private void readObject(java.io.ObjectInputStream stream)
      throws IOException, ClassNotFoundException {}

  private void readObjectNoData() throws ObjectStreamException {}
}

The warnings are:

    [javac] Test.java:27: warning: [UnusedVariable] The parameter 'stream' is never read.
    [javac]   private void readObject(java.io.ObjectInputStream stream)
    [javac]                                                     ^
    [javac]     (see https://errorprone.info/bugpattern/UnusedVariable)
    [javac]   Did you mean 'private void readObject()'?
    [javac] Test.java:25: warning: [UnusedVariable] The parameter 'stream' is never read.
    [javac]   private void writeObject(java.io.ObjectOutputStream stream) throws IOException {}
    [javac]                                                       ^
    [javac]     (see https://errorprone.info/bugpattern/UnusedVariable)
    [javac]   Did you mean 'private void writeObject() throws IOException {}'?
    [javac] Test.java:25: warning: [MethodCanBeStatic] A private method that does not reference the enclosing instance can be static
    [javac]   private void writeObject(java.io.ObjectOutputStream stream) throws IOException {}
    [javac]   ^
    [javac]     (see https://errorprone.info/bugpattern/MethodCanBeStatic)
    [javac]   Did you mean 'private static void writeObject(java.io.ObjectOutputStream stream) throws IOException {}'?

Of course, these methods need to be declared as they are. Please whitelist them.

Having a readObject method that does not use its parameter occurs for example for singletons.

[graememorgan]

Doesn't your class need to implement java.io.Serializable for implementing those methods to be meaningful?

[PhilippWendler]

Of course, but I just forgot to add this to the minimal test case.

UnusedVariable warnings occur even if implements Serializable is added, though the warning from MethodCanBeStatic seems to be gone.

[graememorgan]

Thanks. Will be fixed in the next release.