Resolves #550: New parameter to DisplayPluginUpdatesMojo: processUnbo…

…undPlugins

- if true, will show updates to plugins defined in parent poms, which have no version in the current pom
- false by default to retain backwards compatibility

versions-maven-plugin/src/it/it-display-plugin-updates-issue-533/invoker.properties

@@ -0,0 +1,21 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#
+
+invoker.goals = ${project.groupId}:${project.artifactId}:${project.version}:display-plugin-updates -N
+invoker.mavenOpts = -DprocessUnboundPlugins=true -Dversions.outputFile=output.txt -DoutputEncoding=UTF-8

versions-maven-plugin/src/it/it-display-plugin-updates-issue-533/parent.xml

@@ -0,0 +1,45 @@
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one
+  ~ or more contributor license agreements.  See the NOTICE file
+  ~ distributed with this work for additional information
+  ~ regarding copyright ownership.  The ASF licenses this file
+  ~ to you under the Apache License, Version 2.0 (the
+  ~ "License"); you may not use this file except in compliance
+  ~ with the License.  You may obtain a copy of the License at
+  ~
+  ~     http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing,
+  ~ software distributed under the License is distributed on an
+  ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  ~ KIND, either express or implied.  See the License for the
+  ~ specific language governing permissions and limitations
+  ~ under the License.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>localhost</groupId>
+  <artifactId>it-display-plugin-updates-issue-550-parent</artifactId>
+  <version>1.0</version>
+  <packaging>pom</packaging>
+
+  <prerequisites>
+    <maven>${mavenVersion}</maven>
+  </prerequisites>
+
+  <build>
+    <pluginManagement>
+      <plugins>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-jar-plugin</artifactId>
+          <version>3.0.0</version>
+        </plugin>
+      </plugins>
+    </pluginManagement>
+  </build>
+
+</project>

versions-maven-plugin/src/it/it-display-plugin-updates-issue-533/pom.xml

@@ -0,0 +1,26 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>localhost</groupId>
+    <artifactId>it-display-plugin-updates-issue-550-parent</artifactId>
+    <version>1.0</version>
+    <relativePath>parent.xml</relativePath>
+  </parent>
+
+  <artifactId>it-display-plugin-updates-issue-550</artifactId>
+  <version>1.0</version>
+  <packaging>pom</packaging>
+
+  <build>
+    <pluginManagement>
+      <plugins>
+        <plugin>
+          <artifactId>maven-jar-plugin</artifactId>
+        </plugin>
+      </plugins>
+    </pluginManagement>
+  </build>
+
+</project>

versions-maven-plugin/src/it/it-display-plugin-updates-issue-533/verify.groovy

@@ -0,0 +1,23 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+assert new File(basedir, 'output.txt').text
+        .replaceAll('\r', '')
+        .contains('The following plugin updates are available:\n'
+        + '  maven-jar-plugin ................................... 3.0.0 -> 3.3.0')

versions-maven-plugin/src/main/java/org/codehaus/mojo/versions/DisplayPluginUpdatesMojo.java

@@ -64,6 +64,7 @@
 import org.apache.maven.plugin.MojoExecutionException;
 import org.apache.maven.plugin.MojoFailureException;
 import org.apache.maven.plugins.annotations.Mojo;
+import org.apache.maven.plugins.annotations.Parameter;
 import org.apache.maven.project.MavenProject;
 import org.apache.maven.project.ProjectBuilder;
 import org.apache.maven.project.ProjectBuildingException;
@@ -145,6 +146,17 @@ public class DisplayPluginUpdatesMojo extends AbstractVersionsDisplayMojo {
      */
     protected final ProjectBuilder projectBuilder;
 
+    /**
+     * <p>If set to {@code true}, will also display updates to plugins where no version is specified
+     * in the current POM, but whose version is specified in the parent or the "superpom".</p>
+     * <p>It might not always be possible to update these plugins,
+     * thus the default value of this parameter is {@code false}</p>.
+     *
+     * @since 2.15.0
+     */
+    @Parameter(property = "processUnboundPlugins", defaultValue = "false")
+    protected boolean processUnboundPlugins;
+
     // --------------------- GETTER / SETTER METHODS ---------------------
 
     @Inject
@@ -350,11 +362,11 @@ public void execute() throws MojoExecutionException, MojoFailureException {
             }
 
             boolean versionSpecifiedInCurrentPom = pluginsWithVersionsSpecified.contains(coords);
-            if (!versionSpecifiedInCurrentPom && parentPlugins.containsKey(coords)) {
+            if (!versionSpecifiedInCurrentPom && !processUnboundPlugins && parentPlugins.containsKey(coords)) {
                 getLog().debug("Skip " + coords + ", version " + version + " is defined in parent POM.");
+                getLog().debug("Use the \"processUnboundPlugins\" parameter to see these updates.");
                 continue;
             }
-
             getLog().debug("Checking " + coords + " for updates newer than " + version);
             String effectiveVersion = version;
 
@@ -447,7 +459,7 @@ public void execute() throws MojoExecutionException, MojoFailureException {
             getLog().debug("[" + coords + "].artifactVersion=" + artifactVersion);
             getLog().debug("[" + coords + "].effectiveVersion=" + effectiveVersion);
             getLog().debug("[" + coords + "].specified=" + versionSpecifiedInCurrentPom);
-            if (version == null || !versionSpecifiedInCurrentPom) {
+            if (version == null || (!processUnboundPlugins && !versionSpecifiedInCurrentPom)) {
                 version = superPomPluginManagement.get(coords);
                 getLog().debug("[" + coords + "].superPom.version=" + version);