Consider if we're able to vendor jni.h or not

[ktoso]

We'll have to make sure we're allowed to include the jni.h header file before doing so.

This task is on me specifically, I'll follow up on it.

[marcprux]

I don't know the licensing nuances of a header file that is derived wholly from an open specification, but versions included in projects like Apache Harmony (https://github.com/apache/harmony/blob/trunk/drlvm/vm/include/jni.h) and Google's j2objc (https://github.com/google/j2objc/blob/master/jre_emul/Classes/jni.h) are licensed under Apache 2.0 (same as swift-java and everything else under swiftlang), so there is precedent in vendoring this header.

It doesn't matter that much, but when I last looked at it, all the "search around for JAVA_HOME" logic in Package.swift could be eliminated if we simply included jni.h in this project. It would be doubly-regrettable if we had to duplicate all that logic between swift-java and swift-java-jni-core.

[ktoso]

Yeah it'd be obviously nicer, it's a legal question though so I'm talking to the relevant folks right now. I'll report back

[ktoso]

From quick research: As far as I can see even though jni.h is covered by classpath exception, that is specifically for linking and not distributing, so I don't think we can distributed the header or we'd be subject to GPLv2 which we cannot do.

[marcprux]

I urge further consideration of this. "Java" itself is distributed under a variety of licenses: OpenJDK is GPL, Apache Harmony is Apache 2.0 as is Google's degenerate "Dalvik" variant, and of course Oracle's proprietary license for their own distribution.

But jni.h isn't an integral part of any of these Java distributions per se, nor is it ever technically "linked". It is merely the encoding of rules laid out in the Java specification. As such, I don't think we ought to consider it anything but a byproduct of the specification. We could even clean-room re-implement it ourselves (or the subset of it that we need, i.e., without the C++ stuff) if we think that would make it more palatable.

[ktoso]

Solved by #8