Dynamically apply Add-Opens directives from MANIFEST.MF

src/main/java/org/jenkinsci/maven/plugins/hpi/AbstractJenkinsMojo.java

@@ -1,12 +1,14 @@
 package org.jenkinsci.maven.plugins.hpi;
 
+import edu.umd.cs.findbugs.annotations.CheckForNull;
 import hudson.util.VersionNumber;
 import io.jenkins.lib.versionnumber.JavaSpecificationVersion;
 import java.io.DataInputStream;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.jar.JarFile;
+import java.util.jar.Manifest;
 import java.util.zip.ZipEntry;
 import org.apache.maven.artifact.Artifact;
 import org.apache.maven.artifact.factory.ArtifactFactory;
@@ -140,6 +142,37 @@ private Artifact resolveJenkinsCore() throws MojoExecutionException {
         }
     }
 
+    @CheckForNull
+    protected String getAddOpens() throws MojoExecutionException {
+        Artifact artifact = resolveJenkinsWar();
+        File war = wrap(artifact).getFile();
+        try (JarFile jarFile = new JarFile(war)) {
+            Manifest manifest = jarFile.getManifest();
+            if (manifest == null) {
+                throw new MojoExecutionException("No manifest found in " + war);
+            }
+            return manifest.getMainAttributes().getValue("Add-Opens");
+        } catch (IOException e) {
+            throw new MojoExecutionException("Failed to read MANIFEST.MF from " + war, e);
+        }
+    }
+
+    private Artifact resolveJenkinsWar() throws MojoExecutionException {
+        DefaultArtifactCoordinate artifactCoordinate = new DefaultArtifactCoordinate();
+        artifactCoordinate.setGroupId("org.jenkins-ci.main");
+        artifactCoordinate.setArtifactId("jenkins-war");
+        artifactCoordinate.setVersion(findJenkinsVersion());
+        artifactCoordinate.setExtension("war");
+
+        try {
+            return artifactResolver
+                    .resolveArtifact(session.getProjectBuildingRequest(), artifactCoordinate)
+                    .getArtifact();
+        } catch (ArtifactResolverException e) {
+            throw new MojoExecutionException("Couldn't download artifact: ", e);
+        }
+    }
+
     protected MavenArtifact wrap(Artifact a) {
         return new MavenArtifact(
                 a,

src/main/java/org/jenkinsci/maven/plugins/hpi/InitializeMojo.java

@@ -0,0 +1,44 @@
+package org.jenkinsci.maven.plugins.hpi;
+
+import io.jenkins.lib.versionnumber.JavaSpecificationVersion;
+import java.util.ArrayList;
+import java.util.List;
+import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugins.annotations.LifecyclePhase;
+import org.apache.maven.plugins.annotations.Mojo;
+
+/**
+ * Configure Maven for the desired version of Java.
+ *
+ * @author Basil Crow
+ */
+@Mojo(name = "initialize", defaultPhase = LifecyclePhase.INITIALIZE)
+public class InitializeMojo extends AbstractJenkinsMojo {
+
+    @Override
+    public void execute() throws MojoExecutionException {
+        String addOpens = getAddOpens();
+        if (addOpens != null
+                && JavaSpecificationVersion.forCurrentJVM().isNewerThanOrEqualTo(new JavaSpecificationVersion("9"))) {
+            String argLine = project.getProperties().getProperty("argLine");
+            if (argLine != null) {
+                argLine += " " + buildArgLine(addOpens);
+            } else {
+                argLine = buildArgLine(addOpens);
+            }
+            getLog().info("Setting argLine to " + argLine);
+            project.getProperties().setProperty("argLine", argLine);
+        }
+    }
+
+    private static String buildArgLine(String addOpens) {
+        List<String> arguments = new ArrayList<>();
+        for (String module : addOpens.split("\\s+")) {
+            if (!module.isEmpty()) {
+                arguments.add("--add-opens");
+                arguments.add(module + "=ALL-UNNAMED");
+            }
+        }
+        return String.join(" ", arguments);
+    }
+}

src/main/resources/META-INF/plexus/components.xml

@@ -12,6 +12,7 @@
             <id>default</id>
             <phases>
               <validate>org.jenkins-ci.tools:maven-hpi-plugin:validate,org.jenkins-ci.tools:maven-hpi-plugin:validate-hpi</validate>
+              <initialize>org.jenkins-ci.tools:maven-hpi-plugin:initialize</initialize>
               <process-resources>org.apache.maven.plugins:maven-resources-plugin:resources</process-resources>
               <compile>org.apache.maven.plugins:maven-compiler-plugin:compile</compile>
               <process-classes>org.kohsuke:access-modifier-checker:enforce</process-classes>