This commit modifies the build to require JDK 9 for
compilation. Henceforth, we will compile with a JDK 9 compiler targeting
JDK 8 as the class file format. Optionally, RUNTIME_JAVA_HOME can be set
as the runtime JDK used for running tests. To enable this change, we
separate the meaning of the compiler Java home versus the runtime Java
home. If the runtime Java home is not set (via RUNTIME_JAVA_HOME) then
we fallback to using JAVA_HOME as the runtime Java home. This enables:
- developers only have to set one Java home (JAVA_HOME)
- developers can set an optional Java home (RUNTIME_JAVA_HOME) to test
on the minimum supported runtime
- we can test compiling with JDK 9 running on JDK 8 and compiling with
JDK 9 running on JDK 9 in CI
With Gradle 4.1 and newer JDK versions, we can finally invoke Gradle directly using a JDK9 JAVA_HOME without requiring a JDK8 to "bootstrap" the build. As the thirdPartyAudit task runs within the JVM that Gradle runs in, it needs to be adapted now to be JDK9 aware.
This commit also changes the `JavaCompile` tasks to only fork if necessary (i.e. when Gradle's JVM and JAVA_HOME's JVM differ).
JDK9 removed pathname canonicalization when constructing FilePermission objects, which breaks some of the FilePermissions added by
Elasticsearch. This commit adds the system property jdk.io.permissionsUseCanonicalPath which makes JDK9 behave like JDK8 w.r.t. FilePermissions (see
https://github.com/elastic/elasticsearch/issues/21534).
As discussed at https://github.com/elastic/elasticsearch-cloud-azure/issues/91#issuecomment-229113595, we know that the current `discovery-azure` plugin only works with Azure Classic VMs / Services (which is somehow Legacy now).
The proposal here is to rename `discovery-azure` to `discovery-azure-classic` in case some users are using it.
And deprecate it for 5.0.
Closes#19144.
Jason Tedor
Yannick Welsch
David Pilato