Build: Fix naming conventions task (#31681)

Move min compiler and runtime version to files so we can fix the source
and target comparability of the build script to those

Closes #31665

buildSrc/build.gradle

@@ -16,8 +16,6 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-
-
 import java.nio.file.Files
 
 plugins {
@@ -41,6 +39,12 @@ if (project == rootProject) {
   buildDir = 'build-bootstrap'
 }
 
+// Make sure :buildSrc: doesn't generate classes incompatible with RUNTIME_JAVA_HOME
+// We can't use BuildPlugin here, so read from file
+String minimumRuntimeVersion = file('src/main/resources/minimumRuntimeVersion').text.trim()
+targetCompatibility = minimumRuntimeVersion
+sourceCompatibility = minimumRuntimeVersion
+
 /*****************************************************************************
  *         Propagating version.properties to the rest of the build           *
  *****************************************************************************/

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -19,7 +19,6 @@
 package org.elasticsearch.gradle
 
 import com.carrotsearch.gradle.junit4.RandomizedTestingTask
-import nebula.plugin.extraconfigurations.ProvidedBasePlugin
 import org.apache.tools.ant.taskdefs.condition.Os
 import org.eclipse.jgit.lib.Constants
 import org.eclipse.jgit.lib.RepositoryBuilder
@@ -58,9 +57,6 @@ import java.time.ZonedDateTime
  */
 class BuildPlugin implements Plugin<Project> {
 
-    static final JavaVersion minimumRuntimeVersion = JavaVersion.VERSION_1_8
-    static final JavaVersion minimumCompilerVersion = JavaVersion.VERSION_1_10
-
     @Override
     void apply(Project project) {
         if (project.pluginManager.hasPlugin('elasticsearch.standalone-rest-test')) {
@@ -95,6 +91,12 @@ class BuildPlugin implements Plugin<Project> {
     /** Performs checks on the build environment and prints information about the build environment. */
     static void globalBuildInfo(Project project) {
         if (project.rootProject.ext.has('buildChecksDone') == false) {
+            JavaVersion minimumRuntimeVersion = JavaVersion.toVersion(
+                    BuildPlugin.class.getClassLoader().getResourceAsStream("minimumRuntimeVersion").text.trim()
+            )
+            JavaVersion minimumCompilerVersion = JavaVersion.toVersion(
+                    BuildPlugin.class.getClassLoader().getResourceAsStream("minimumCompilerVersion").text.trim()
+            )
             String compilerJavaHome = findCompilerJavaHome()
             String runtimeJavaHome = findRuntimeJavaHome(compilerJavaHome)
             File gradleJavaHome = Jvm.current().javaHome
@@ -192,10 +194,12 @@ class BuildPlugin implements Plugin<Project> {
             project.rootProject.ext.runtimeJavaVersion = runtimeJavaVersionEnum
             project.rootProject.ext.javaVersions = javaVersions
             project.rootProject.ext.buildChecksDone = true
+            project.rootProject.ext.minimumCompilerVersion = minimumCompilerVersion
+            project.rootProject.ext.minimumRuntimeVersion = minimumRuntimeVersion
         }
 
-        project.targetCompatibility = minimumRuntimeVersion
+        project.targetCompatibility = project.rootProject.ext.minimumRuntimeVersion
-        project.sourceCompatibility = minimumRuntimeVersion
+        project.sourceCompatibility = project.rootProject.ext.minimumRuntimeVersion
 
         // set java home for each project, so they dont have to find it in the root project
         project.ext.compilerJavaHome = project.rootProject.ext.compilerJavaHome
@@ -348,7 +352,7 @@ class BuildPlugin implements Plugin<Project> {
                 // just a self contained test-fixture configuration, likely transitive and hellacious
                 return
             }
-            configuration.resolutionStrategy { 
+            configuration.resolutionStrategy {
                 failOnVersionConflict()
             }
         })

buildSrc/src/main/resources/minimumCompilerVersion

@@ -0,0 +1 @@
+1.10

buildSrc/src/main/resources/minimumRuntimeVersion

@@ -0,0 +1 @@
+1.8

buildSrc/src/test/java/org/elasticsearch/gradle/precommit/NamingConventionsTaskIT.java

@@ -4,7 +4,6 @@ import org.elasticsearch.gradle.test.GradleIntegrationTestCase;
 import org.gradle.testkit.runner.BuildResult;
 import org.gradle.testkit.runner.GradleRunner;
 import org.gradle.testkit.runner.TaskOutcome;
-import org.junit.Ignore;
 
 import java.util.Arrays;
 
@@ -22,7 +21,6 @@ public class NamingConventionsTaskIT extends GradleIntegrationTestCase {
         assertTrue(output, output.contains("build plugin can be applied"));
     }
 
-    @Ignore("AwaitsFix : https://github.com/elastic/elasticsearch/issues/31665")
     public void testNameCheckFailsAsItShould() {
         BuildResult result = GradleRunner.create()
             .withProjectDir(getProjectDir("namingConventionsSelfTest"))
@@ -48,7 +46,6 @@ public class NamingConventionsTaskIT extends GradleIntegrationTestCase {
         }
     }
 
-    @Ignore("AwaitsFix : https://github.com/elastic/elasticsearch/issues/31665")
     public void testNameCheckFailsAsItShouldWithMain() {
         BuildResult result = GradleRunner.create()
             .withProjectDir(getProjectDir("namingConventionsSelfTest"))