Fix es-core build.gradle for the 9 MR jar

Author: dakrone

libs/elasticsearch-core/build.gradle

@@ -26,6 +26,45 @@ apply plugin: 'nebula.maven-scm'
 
 archivesBaseName = 'elasticsearch-core'
 
+// we want to keep the JDKs in our IDEs set to JDK 8 until minimum JDK is bumped to 9 so we do not include this source set in our IDEs
+if (!isEclipse && !isIdea) {
+    sourceSets {
+        java9 {
+            java {
+                srcDirs = ['src/main/java9']
+            }
+        }
+    }
+
+    configurations {
+        java9Compile.extendsFrom(compile)
+    }
+
+    dependencies {
+        java9Compile sourceSets.main.output
+    }
+
+    compileJava9Java {
+        sourceCompatibility = 9
+        targetCompatibility = 9
+    }
+
+    /* Enable this when forbiddenapis was updated to 2.6.
+     * See: https://github.com/elastic/elasticsearch/issues/29292
+    forbiddenApisJava9 {
+        targetCompatibility = 9
+    }
+     */
+
+    jar {
+        metaInf {
+            into 'versions/9'
+            from sourceSets.java9.output
+        }
+        manifest.attributes('Multi-Release': 'true')
+    }
+}
+
 publishing {
     publications {
         nebula {
@@ -39,6 +78,10 @@ dependencies {
     testCompile "junit:junit:${versions.junit}"
     testCompile "org.hamcrest:hamcrest-all:${versions.hamcrest}"
 
+    if (!isEclipse && !isIdea) {
+        java9Compile sourceSets.main.output
+    }
+
     if (isEclipse == false || project.path == ":libs:elasticsearch-core-tests") {
         testCompile("org.elasticsearch.test:framework:${version}") {
             exclude group: 'org.elasticsearch', module: 'elasticsearch-core'
@@ -52,29 +95,6 @@ forbiddenApisMain {
     signaturesURLs = [PrecommitTasks.getResource('/forbidden/jdk-signatures.txt')]
 }
 
-// we want to keep the JDKs in our IDEs set to JDK 8 until minimum JDK is bumped to 9 so we do not include this source set in our IDEs
-if (!isEclipse && !isIdea) {
-    sourceSets {
-        java9 {
-            java {
-                srcDirs = ['src/main/java9']
-            }
-        }
-    }
-
-    compileJava9Java {
-        sourceCompatibility = 9
-        targetCompatibility = 9
-    }
-
-    jar {
-        into('META-INF/versions/9') {
-            from sourceSets.java9.output
-        }
-        manifest.attributes('Multi-Release': 'true')
-    }
-}
-
 if (isEclipse) {
     // in eclipse the project is under a fake root, we need to change around the source sets
     sourceSets {