Provision min runtime version jdk for compilation (#105152)

This commit adjusts compile tasks to explicitly provision a Java
toolchain for the Java minimum runtime version. By doing so the Java
used by Gradle may be upgraded without the possibility of causing
spurious warnings from javac which could fail the build, such as when
new warnings are added in later JDK versions.

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/ElasticsearchJavaBasePlugin.java

@@ -26,14 +26,26 @@
 import org.gradle.api.tasks.compile.CompileOptions;
 import org.gradle.api.tasks.compile.GroovyCompile;
 import org.gradle.api.tasks.compile.JavaCompile;
+import org.gradle.jvm.toolchain.JavaLanguageVersion;
+import org.gradle.jvm.toolchain.JavaToolchainService;
 
 import java.util.List;
 
+import javax.inject.Inject;
+
 /**
  * A wrapper around Gradle's Java Base plugin that applies our
  * common configuration for production code.
  */
 public class ElasticsearchJavaBasePlugin implements Plugin<Project> {
+
+    private final JavaToolchainService javaToolchains;
+
+    @Inject
+    ElasticsearchJavaBasePlugin(JavaToolchainService javaToolchains) {
+        this.javaToolchains = javaToolchains;
+    }
+
     @Override
     public void apply(Project project) {
         // make sure the global build info plugin is applied to the root project
@@ -103,7 +115,7 @@ private static void disableTransitiveDependenciesForSourceSet(Project project, S
     /**
      * Adds compiler settings to the project
      */
-    public static void configureCompile(Project project) {
+    public void configureCompile(Project project) {
         project.getExtensions().getExtraProperties().set("compactProfile", "full");
         JavaPluginExtension java = project.getExtensions().getByType(JavaPluginExtension.class);
         if (BuildParams.getJavaToolChainSpec().isPresent()) {
@@ -112,6 +124,10 @@ public static void configureCompile(Project project) {
         java.setSourceCompatibility(BuildParams.getMinimumRuntimeVersion());
         java.setTargetCompatibility(BuildParams.getMinimumRuntimeVersion());
         project.getTasks().withType(JavaCompile.class).configureEach(compileTask -> {
+            compileTask.getJavaCompiler().set(javaToolchains.compilerFor(spec -> {
+                spec.getLanguageVersion().set(JavaLanguageVersion.of(BuildParams.getMinimumRuntimeVersion().getMajorVersion()));
+            }));
+
             CompileOptions compileOptions = compileTask.getOptions();
             /*
              * -path because gradle will send in paths that don't always exist.

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/MrjarPlugin.java

@@ -11,7 +11,6 @@
 import org.elasticsearch.gradle.util.GradleUtils;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
-import org.gradle.api.plugins.JavaLibraryPlugin;
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.plugins.JavaPluginExtension;
 import org.gradle.api.tasks.SourceSet;
@@ -50,7 +49,7 @@ public class MrjarPlugin implements Plugin<Project> {
 
     @Override
     public void apply(Project project) {
-        project.getPluginManager().apply(JavaLibraryPlugin.class);
+        project.getPluginManager().apply(ElasticsearchJavaBasePlugin.class);
         var javaExtension = project.getExtensions().getByType(JavaPluginExtension.class);
 
         var srcDir = project.getProjectDir().toPath().resolve("src");