Ant JunitTask update to support JDK9 modules

[Alex Buckley]

On 4/27/2016 1:41 PM, Jan Lahoda wrote:
> On 27.4.2016 21:30, Alex Buckley wrote:
>> Your changes skyrocket in complexity because your Ant setup involves
>> both ant-junit.jar and ant-junit4.jar. The JUnit task documentation
>> (https://ant.apache.org/manual/Tasks/junit.html) doesn't suggest this is
>> necessary or desirable. It's either pointless or dangerous to have both
>> JARs on the classpath, which is why the module system rejects them as
>
> I think it would be useful if you could elaborate on why using both
> ant-junit.jar and ant-junit4.jar is pointless or dangerous. What I see
> in the jars, the org.apache.tools.ant.taskdefs.optional.junit package is
> perfectly partitioned between the jars (there is no class that would be
> in both jars). It seems ant-junit4.jar cannot work by itself, without
> ant-junit.jar. I am not 100% sure what ant-junit4.jar does, but it seems
> it aids in running single test method in a JUnit 4 way. There appears to
> be some fallback to JUnit 3 style if the JUnit 4 style is not available,
> but it is hard to say if that is sufficient. So dropping (the content
> of) ant-junit4.jar would mean at least careful testing, but more
> probably a loss of a significant feature.

Perfect partitioning of a split package is uncommon. The common case is 
some overlap of types, leading to obscure mix-and-match problems, so the 
module system rejects a split package unconditionally. Ant's 
redistribution of JUnit JARs (or perhaps its JUnit's own scheme for 
v3-to-v4 migration) is architected in a way that's at odds with the 
module system.

It might be possible to make a case for relaxing the anti-split-package 
provision for automatic modules, since they're coming from the classpath 
world where every artifact is "open" to combination with artifacts 
elsewhere on the path. But that would reduce reliability, since 
generally it's a _feature_ that the module system warns:

java.lang.module.ResolutionException: Modules ant.junit4 and ant.junit 
export package org.apache.tools.ant.taskdefs.optional.junit
to module hamcrest.core

Alex