Ignore Varargs Warnings In Javac - ant

Question

I want to escalate the missing serialversionUID warning to an error and fail my build when it occurs in javac.
I have added the following to my ant task:
<compilerarg value="-Xlint:serial"/>
<compilerarg value="-Werror"/>
However, the build also fails with varargs warnings:
non-varargs call of varargs method with inexact argument type for last parameter;
cast to java.lang.Object for a varargs call
cast to java.lang.Object[] for a non-varargs call and to suppress this warning
I tried changing the javac task to
<compilerarg value="-Xlint:-varargs"/>
<compilerarg value="-Xlint:serial"/>
<compilerarg value="-Werror"/>
However, it made no difference. How do I make the compiler ignore these warnings and only fail on the serialversionUID?
I am using Ant 1.9.4 and tried with Javac 1.6u37, 1.7u79 and 1.8u92
Example class:
package com.stackoverflow.compiler;
import java.io.Serializable;
public class Main implements Serializable {
public static void foo(Object... args) {
System.out.println("Test foo");
}
public static void main(String[] args) {
// is args supposed to be an array of objects
// or the only element in an array?
foo(args);
}
}

Answer 1

It seems that the warning you have is not related to the -Xlint:varargs option
According to javac reference the varargs option for -Xlint:
Warns about unsafe usages of variable arguments (varargs) methods, in particular, those that contain non-reifiable arguments
The documentation says that the following code:
public class ArrayBuilder {
public static <T> void addToList (List<T> listArg, T... elements) {
for (T x : elements) {
listArg.add(x);
}
}
}
should produce the warning:
warning: [varargs] Possible heap pollution from parameterized vararg type T
The actual warning I get (using javac 1.8.0_65) is:
warning: [unchecked] Possible heap pollution from parameterized vararg type T
(i.e unchecked instead of varargs)
The warning you got can be caused by code like this:
public static void foo(Object... args) {...}
public static void main(String[] args) {
// is args supposed to be an array of objects
// or the only element in an array?
foo(args);
}
That warning went away only using -Xlint:none option, but then -Xlint:serial does nothing. So it seems what you want is not possible.

Answer 2

I know the question is about javac, but let me still mention that ecj can be configured to meet your requirement: simply say -err:serial on the command line.
With that option this source file
public class Serial implements java.io.Serializable {}
will trigger this compiler output
----------
1. ERROR in /tmp/Serial.java (at line 1)
public class Serial implements java.io.Serializable {}
^^^^^^
The serializable class Serial does not declare a static final serialVersionUID field of type long
----------
1 problem (1 error)
Other warnings are not affected by that option. In particular, you could complete suppress the varargs warning by adding -warn:-varargsCast. This isn't necessary because a warning will never let your build fail. But if you really don't want to see this even as a warning, the full command line would look like this:
ecj -err:serial -warn:-varargsCast Main.java
See the JDT FAQ for using ecj in automated builds, incl. ant.