Using --release compiler option vs -source and -target

[tpietzsch]

I ran into a problem with building BigVolumeViewer with JDK 11 (and Maven).

pietzsch@mycroft:~/workspace/bigdataviewer/bigvolumeviewer-core (master)$ mvn clean install                                                                                                           # 1 [15:22:38]
[INFO] Scanning for projects...
[INFO]
[INFO] ----------------------< sc.fiji:bigvolumeviewer >-----------------------
[INFO] Building BigVolumeViewer 0.3.2-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
...
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ bigvolumeviewer ---
[INFO] Compiling 103 source files to /Users/pietzsch/workspace/bigdataviewer/bigvolumeviewer-core/target/classes
[INFO] /Users/pietzsch/workspace/bigdataviewer/bigvolumeviewer-core/src/main/java/bvv/vistools/BvvFunctions.java: Some input files use or override a deprecated API.
[INFO] /Users/pietzsch/workspace/bigdataviewer/bigvolumeviewer-core/src/main/java/bvv/vistools/BvvFunctions.java: Recompile with -Xlint:deprecation for details.
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /Users/pietzsch/workspace/bigdataviewer/bigvolumeviewer-core/src/main/java/bvv/core/blocks/ByteUtils.java:[36,16] package sun.misc does not exist
[ERROR] /Users/pietzsch/workspace/bigdataviewer/bigvolumeviewer-core/src/main/java/bvv/core/blocks/ByteUtils.java:[41,30] cannot find symbol
  symbol:   class Unsafe
  location: class bvv.core.blocks.ByteUtils
[INFO] 2 errors
[INFO] -------------------------------------------------------------
...

This can be traced back to the maven-compiler-plugin configuring javac with --release 8.

The problem is that --release 8 works slightly different that the old-style -source 1.8 -target 1.8.
See https://bugs.openjdk.org/browse/JDK-8214165, https://bugs.openjdk.org/browse/JDK-8206937, https://mail.openjdk.org/pipermail/compiler-dev/2018-January/011583.html.
The spec for --release N is to provide access to the public documented API for JDK N. The sun.misc package is not public documented API.

Ironically, if we were targeting Java 11, there would be no problem. --release 11 would work, because there is the jdk.unsupported module ...

Anyway... I think this can be traced to

pom-scijava-base/pom.xml

Lines 2107 to 2125 in 8920b4f

	<profile>
	<id>java-9</id>
	<activation>
	<jdk>[9,)</jdk>
	</activation>
	<properties>
	<maven.compiler.release>${scijava.jvm.version}</maven.compiler.release>
	</properties>
	<build>
	<plugins>
	<plugin>
	<artifactId>maven-javadoc-plugin</artifactId>
	<configuration>
	<javadocExecutable>${java.home}/bin/javadoc</javadocExecutable>
	</configuration>
	</plugin>
	</plugins>
	</build>
	</profile>

where the <maven.compiler.release> property is set.

The only way I found to fix that in BigVolumeViewer's pom.xml is bigdataviewer/bigvolumeviewer-core@ffaf291
https://github.com/bigdataviewer/bigvolumeviewer-core/blob/ffaf291987da4ea3e4ca9796a700b43c5209c8be/pom.xml#L83-L95

It would be nicer to address this higher up, but I don't know how pom-scijava-base should be changed exactly, and what side effects would be.