Suppress spurious SDK builds

[kennknowles]

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This is a low tech solution that mostly keeps the status quo but seems to eliminate the extra builds. The current method won't work if the SDK is ever shaded, since it depends on absolute paths in magic strings, but this PR doesn't try to solve that problem.

[kennknowles]

R: @lukecwik

[kennknowles]

The new excludes section overrides the global one, so I had to repeat here. If you have a maven tip to avoid it, I'm happy to accept.

[davorbonaci]

Not possible, AFAIK.

[kennknowles]

No longer needed. Thanks for the pkginfo tip.

[davorbonaci]

R: @davorbonaci

May I ask what's the impact here? Those are static, rarely changing files. What would we gain with this?

[kennknowles]

I presume you mean all the package-info.java, since sdk.properties is a nonce, always changing.

Since package-info.java does not produce a .class file, they are viewed as always out-of-date according to maven.

[lukecwik]

As Kenn said, the compiler always re-runs because it thinks there is a missing class file, alternatively we could tell the java compiler to always produce package-info classes via -Xpkginfo:always, but that is a non-standard option so I think filtering them out is better.

[kennknowles]

Ping, let's add R: @davorbonaci

This is a nearly no-op change that actually just suppresses a maven bug.

[davorbonaci]

I think I'd prefer -Xpkginfo:always over the exclusion.

[kennknowles]

Agreed & done.

[kennknowles]

Pretty exciting. Looks like the current status causes a bug in the Java 7 compilers on Linux & Mac :-)

[kennknowles]

Please take another look. This can actually save many minutes for anyone using command-line mvn, which I have to do once in a while.

[lukecwik]

The travis builds are failing with an exception in the compiler, I don't think we can check this in.

[kennknowles]

Agreed. Really curious.

[kennknowles]

Looks like it is just a total bug, not fixed until Java 8: https://bugs.openjdk.java.net/browse/JDK-8022161

[kennknowles]

Looks like -Xpkginfo:nonempty is not going to cut it, so the idea of incremental builds requires littering annotations. I don't feel like doing that, so I'm just going to give up on fixing the build.