Use minimum java version for javadoc tool (#118908)

When compiling we use a compiler for the minimum java version. However,
javadoc is left to whatever Java gradle uses. This commit adjusts
javadoc to also use a javadoc tool for the minimum java version.

Author: rjernst

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

@@ -31,11 +31,15 @@
 import org.gradle.api.tasks.bundling.Jar;
 import org.gradle.api.tasks.javadoc.Javadoc;
 import org.gradle.external.javadoc.CoreJavadocOptions;
+import org.gradle.jvm.toolchain.JavaLanguageVersion;
+import org.gradle.jvm.toolchain.JavaToolchainService;
 import org.gradle.language.base.plugins.LifecycleBasePlugin;
 
 import java.io.File;
 import java.util.Map;
 
+import javax.inject.Inject;
+
 import static org.elasticsearch.gradle.internal.conventions.util.Util.toStringable;
 import static org.elasticsearch.gradle.internal.util.ParamsUtils.loadBuildParams;
 
@@ -44,6 +48,14 @@
  * common configuration for production code.
  */
 public class ElasticsearchJavaPlugin implements Plugin<Project> {
+
+    private final JavaToolchainService javaToolchains;
+
+    @Inject
+    ElasticsearchJavaPlugin(JavaToolchainService javaToolchains) {
+        this.javaToolchains = javaToolchains;
+    }
+
     @Override
     public void apply(Project project) {
         project.getRootProject().getPlugins().apply(GlobalBuildInfoPlugin.class);
@@ -55,7 +67,7 @@ public void apply(Project project) {
         // configureConfigurations(project);
         configureJars(project, buildParams.get());
         configureJarManifest(project, buildParams.get());
-        configureJavadoc(project);
+        configureJavadoc(project, buildParams.get());
         testCompileOnlyDeps(project);
     }
 
@@ -128,14 +140,18 @@ private static void configureJarManifest(Project project, BuildParameterExtensio
         project.getPluginManager().apply("nebula.info-jar");
     }
 
-    private static void configureJavadoc(Project project) {
+    private void configureJavadoc(Project project, BuildParameterExtension buildParams) {
         project.getTasks().withType(Javadoc.class).configureEach(javadoc -> {
             /*
              * Generate docs using html5 to suppress a warning from `javadoc`
              * that the default will change to html5 in the future.
              */
             CoreJavadocOptions javadocOptions = (CoreJavadocOptions) javadoc.getOptions();
             javadocOptions.addBooleanOption("html5", true);
+
+            javadoc.getJavadocTool().set(javaToolchains.javadocToolFor(spec -> {
+                spec.getLanguageVersion().set(JavaLanguageVersion.of(buildParams.getMinimumRuntimeVersion().getMajorVersion()));
+            }));
         });
 
         TaskProvider<Javadoc> javadoc = project.getTasks().withType(Javadoc.class).named("javadoc");

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

@@ -86,14 +86,14 @@ public void apply(Project project) {
             configurePreviewFeatures(project, javaExtension.getSourceSets().getByName(SourceSet.TEST_SOURCE_SET_NAME), 21);
             for (int javaVersion : mainVersions) {
                 String mainSourceSetName = SourceSet.MAIN_SOURCE_SET_NAME + javaVersion;
-                SourceSet mainSourceSet = addSourceSet(project, javaExtension, mainSourceSetName, mainSourceSets, javaVersion);
+                SourceSet mainSourceSet = addSourceSet(project, javaExtension, mainSourceSetName, mainSourceSets, javaVersion, true);
                 configureSourceSetInJar(project, mainSourceSet, javaVersion);
                 addJar(project, mainSourceSet, javaVersion);
                 mainSourceSets.add(mainSourceSetName);
                 testSourceSets.add(mainSourceSetName);
 
                 String testSourceSetName = SourceSet.TEST_SOURCE_SET_NAME + javaVersion;
-                SourceSet testSourceSet = addSourceSet(project, javaExtension, testSourceSetName, testSourceSets, javaVersion);
+                SourceSet testSourceSet = addSourceSet(project, javaExtension, testSourceSetName, testSourceSets, javaVersion, false);
                 testSourceSets.add(testSourceSetName);
                 createTestTask(project, buildParams, testSourceSet, javaVersion, mainSourceSets);
             }
@@ -121,7 +121,8 @@ private SourceSet addSourceSet(
         JavaPluginExtension javaExtension,
         String sourceSetName,
         List<String> parentSourceSets,
-        int javaVersion
+        int javaVersion,
+        boolean isMainSourceSet
     ) {
         SourceSet sourceSet = javaExtension.getSourceSets().maybeCreate(sourceSetName);
         for (String parentSourceSetName : parentSourceSets) {
@@ -135,6 +136,13 @@ private SourceSet addSourceSet(
             CompileOptions compileOptions = compileTask.getOptions();
             compileOptions.getRelease().set(javaVersion);
         });
+        if (isMainSourceSet) {
+            project.getTasks().create(sourceSet.getJavadocTaskName(), Javadoc.class, javadocTask -> {
+                javadocTask.getJavadocTool().set(javaToolchains.javadocToolFor(spec -> {
+                    spec.getLanguageVersion().set(JavaLanguageVersion.of(javaVersion));
+                }));
+            });
+        }
         configurePreviewFeatures(project, sourceSet, javaVersion);
 
         // Since we configure MRJAR sourcesets to allow preview apis, class signatures for those