Affects Version/s: None
Fix Version/s: 3.8.0
Java 9 allows for JRE version specific code in the form of "multi-release jars"
Older JREs will treat them as normal jars, while newer JREs will load the appropriate specific classes. AFAICT, maven does not currently support this.
Compiler plugin should automatically detect when there are multiple source levels and set MRJAR=True in the manifest.
Source directories could potentially be src/main/java, src/main/java9, src/main/java10, etc. These probably need to be configurable as well, or some deeper discussion about what makes sense and is intuitive for users.