Since ES 8.0.0 upstream stopped distributing a 'no-JDK' package.
This requires us to set `ES_JAVA_HOME` else it fails to find the
JDK that we unbundled and will not start.
--- a/bin/elasticsearch-env
+++ b/bin/elasticsearch-env
@@ -36,6 +36,18 @@ ES_HOME=`dirname "$ES_HOME"`
 ES_CLASSPATH="$ES_HOME/lib/*"
 LAUNCHERS_CLASSPATH="$ES_CLASSPATH:$ES_HOME/lib/launchers/*"
 
+# Set our JVM in a Gentoo-specific manner
+if [ -z "$ES_JAVA_HOME" ]; then
+  GENTOO_VM=$(depend-java-query --get-vm virtual/jre:17)
+  if [ ! -z "$GENTOO_VM" ]; then
+    ES_JAVA_HOME=$(java-config-2 --select-vm=${GENTOO_VM} --jre-home)
+  else
+    echo "Unable to automatically detect a supported Java 17 VM. Elasticsearch is unlikely to launch."
+    echo "Please ensure that you have installed an appropriate Java VM using portage"
+    echo "OR pass the ES_JAVA_HOME environment variable."
+  fi
+fi
+
 # now set the path to java
 if [ ! -z "$ES_JAVA_HOME" ]; then
   JAVA="$ES_JAVA_HOME/bin/java"