feat(java17): conditional compilation to Java 17 bytecode

spinnaker-project-plugin/build.gradle

@@ -5,6 +5,7 @@ dependencies {
   implementation 'org.owasp:dependency-check-gradle:5.1.0'
   implementation "com.diffplug.spotless:spotless-plugin-gradle:5.17.1"
   implementation 'org.eclipse.jgit:org.eclipse.jgit:5.4.0.201906121030-r'
+  implementation 'com.netflix.nebula:gradle-java-cross-compile-plugin:8.0.0'
   implementation 'com.netflix.nebula:gradle-ospackage-plugin:8.4.1'
   implementation 'gradle.plugin.com.google.cloud.artifactregistry:artifactregistry-gradle-plugin:2.1.1'
   implementation platform('com.google.cloud:libraries-bom:26.1.4')

spinnaker-project-plugin/src/main/groovy/com/netflix/spinnaker/gradle/Flags.groovy

@@ -0,0 +1,26 @@
+package com.netflix.spinnaker.gradle
+
+import org.gradle.api.Project
+
+class Flags {
+
+  /**
+   * Whether or not the {@code targetJava17} property was set.
+   */
+  static boolean targetJava17(Project project) {
+    return Boolean.valueOf(project.findProperty("targetJava17")?.toString())
+  }
+
+  /**
+   * Whether cross-compilation should be enabled.
+   *
+   * Determined by the project property 'enableCrossCompilerPlugin', and
+   * disabled by default.
+   *
+   * @param project the project from which to read the property
+   * @return whether cross-compilation should be enabled
+   */
+  static boolean shouldEnableCrossCompilation(Project project) {
+    return Boolean.valueOf(project.findProperty("enableCrossCompilerPlugin")?.toString())
+  }
+}

spinnaker-project-plugin/src/main/groovy/com/netflix/spinnaker/gradle/baseproject/SpinnakerBaseProjectConventionsPlugin.groovy

@@ -1,6 +1,6 @@
 package com.netflix.spinnaker.gradle.baseproject
 
-
+import com.netflix.spinnaker.gradle.Flags
 import groovy.transform.CompileStatic
 import org.gradle.api.JavaVersion
 import org.gradle.api.Plugin
@@ -19,12 +19,14 @@ import org.gradle.jvm.tasks.Jar
 class SpinnakerBaseProjectConventionsPlugin implements Plugin<Project> {
     @Override
     void apply(Project project) {
+      def javaVersion = Flags.targetJava17(project) ? JavaVersion.VERSION_17 : JavaVersion.VERSION_11
+
       project.plugins.withType(JavaBasePlugin) {
         project.plugins.apply(MavenPublishPlugin)
         project.repositories.mavenCentral()
         JavaPluginConvention convention = project.convention.getPlugin(JavaPluginConvention)
-        convention.sourceCompatibility = JavaVersion.VERSION_11
-        convention.targetCompatibility = JavaVersion.VERSION_11
+        convention.sourceCompatibility = javaVersion
+        convention.targetCompatibility = javaVersion
       }
       project.plugins.withType(JavaLibraryPlugin) {
         JavaPluginConvention convention = project.convention.getPlugin(JavaPluginConvention)

spinnaker-project-plugin/src/main/groovy/com/netflix/spinnaker/gradle/baseproject/SpinnakerBaseProjectPlugin.groovy

@@ -1,9 +1,11 @@
 package com.netflix.spinnaker.gradle.baseproject
 
+import com.netflix.spinnaker.gradle.Flags
 import com.netflix.spinnaker.gradle.codestyle.SpinnakerCodeStylePlugin
 import com.netflix.spinnaker.gradle.idea.SpinnakerIdeaConfigPlugin
 import com.netflix.spinnaker.gradle.idea.SpinnakerNewIdeaProjectPlugin
 import com.netflix.spinnaker.gradle.license.SpinnakerLicenseReportPlugin
+import nebula.plugin.compile.JavaCrossCompilePlugin
 import org.gradle.api.Plugin
 import org.gradle.api.Project
 import org.owasp.dependencycheck.gradle.DependencyCheckPlugin
@@ -17,5 +19,8 @@ class SpinnakerBaseProjectPlugin implements Plugin<Project> {
         project.plugins.apply(SpinnakerLicenseReportPlugin)
         project.plugins.apply(DependencyCheckPlugin)
         project.plugins.apply(SpinnakerCodeStylePlugin)
+        if (Flags.shouldEnableCrossCompilation(project)) {
+          project.plugins.apply(JavaCrossCompilePlugin)
+        }
     }
 }