[MNG-6776] Inconsistent list of parameters for MojoDescriptor (#584)

It may lead to confusion as parameters (list) and
parametersMap (map) may "fall apart" easily.

Also, parametersMap did not honor parameter
ordering while parameters list makes it look
that order is important.
Simply, rebuild the map always and retain
ordering as well.

Added UT and also removed some cruft provided
by java8.

Co-authored-by: Marc Wrobel <marc.wrobel@gmail.com>
Co-authored-by: Slawomir Jaranowski <s.jaranowski@gmail.com>

(cherry picked from commit cc51006)
(cherry picked from commit 5ce5591)
(cherry picked from commit 47e2d68)
---

https://issues.apache.org/jira/browse/MNG-7309

maven-plugin-api/src/main/java/org/apache/maven/plugin/descriptor/MojoDescriptor.java

@@ -18,10 +18,11 @@
  */
 package org.apache.maven.plugin.descriptor;
 
-import java.util.HashMap;
-import java.util.LinkedList;
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 
 import org.apache.maven.plugin.Mojo;
 import org.codehaus.plexus.component.repository.ComponentDescriptor;
@@ -51,9 +52,7 @@ public class MojoDescriptor extends ComponentDescriptor<Mojo> implements Cloneab
 
     private static final String DEFAULT_LANGUAGE = "java";
 
-    private List<Parameter> parameters;
-
-    private Map<String, Parameter> parameterMap;
+    private final ArrayList<Parameter> parameters;
 
     /** By default, the execution strategy is "once-per-session" */
     private String executionStrategy = SINGLE_PASS_EXEC_STRATEGY;
@@ -91,7 +90,7 @@ public class MojoDescriptor extends ComponentDescriptor<Mojo> implements Cloneab
     private String deprecated;
 
     /**
-     * Flags this Mojo to run it in a multi module way, i.e. aggregate the build with the set of projects listed as
+     * Flags this Mojo to run it in a multi-module way, i.e. aggregate the build with the set of projects listed as
      * modules. By default, no need to aggregate the Maven project and its child modules
      */
     private boolean aggregator = false;
@@ -140,6 +139,7 @@ public class MojoDescriptor extends ComponentDescriptor<Mojo> implements Cloneab
      * Default constructor.
      */
     public MojoDescriptor() {
+        this.parameters = new ArrayList<>();
         setInstantiationStrategy(DEFAULT_INSTANTIATION_STRATEGY);
         setComponentFactory(DEFAULT_LANGUAGE);
     }
@@ -177,17 +177,19 @@ public void setDeprecated(String deprecated) {
     }
 
     /**
-     * @return the list of parameters
+     * @return the list of parameters copy. Any change to returned list is NOT reflected on this instance. To add
+     * parameters, use {@link #addParameter(Parameter)} method.
      */
     public List<Parameter> getParameters() {
-        return parameters;
+        return new ArrayList<>(parameters);
     }
 
     /**
      * @param parameters the new list of parameters
      * @throws DuplicateParameterException if any
      */
     public void setParameters(List<Parameter> parameters) throws DuplicateParameterException {
+        this.parameters.clear();
         for (Parameter parameter : parameters) {
             addParameter(parameter);
         }
@@ -198,31 +200,25 @@ public void setParameters(List<Parameter> parameters) throws DuplicateParameterE
      * @throws DuplicateParameterException if any
      */
     public void addParameter(Parameter parameter) throws DuplicateParameterException {
-        if (parameters != null && parameters.contains(parameter)) {
+        if (parameters.contains(parameter)) {
             throw new DuplicateParameterException(parameter.getName()
                     + " has been declared multiple times in mojo with goal: " + getGoal() + " (implementation: "
                     + getImplementation() + ")");
         }
 
-        if (parameters == null) {
-            parameters = new LinkedList<>();
-        }
-
         parameters.add(parameter);
     }
 
     /**
-     * @return the list parameters as a Map
+     * @return the list parameters as a Map (keyed by {@link Parameter#getName()}) that is built from
+     * {@link #parameters} list on each call. In other words, the map returned is built on fly and is a copy.
+     * Any change to this map is NOT reflected on list and other way around!
      */
     public Map<String, Parameter> getParameterMap() {
-        if (parameterMap == null) {
-            parameterMap = new HashMap<>();
-
-            if (parameters != null) {
-                for (Parameter pd : parameters) {
-                    parameterMap.put(pd.getName(), pd);
-                }
-            }
+        LinkedHashMap<String, Parameter> parameterMap = new LinkedHashMap<>();
+
+        for (Parameter pd : parameters) {
+            parameterMap.put(pd.getName(), pd);
         }
 
         return parameterMap;
@@ -321,14 +317,14 @@ public boolean requiresOnline() {
     }
 
     /**
-     * @return the binded phase name of the Mojo
+     * @return the bound phase name of the Mojo
      */
     public String getPhase() {
         return phase;
     }
 
     /**
-     * @param phase the new binded phase name of the Mojo
+     * @param phase the new bound phase name of the Mojo
      */
     public void setPhase(String phase) {
         this.phase = phase;
@@ -482,45 +478,16 @@ public boolean equals(Object object) {
         if (object instanceof MojoDescriptor) {
             MojoDescriptor other = (MojoDescriptor) object;
 
-            if (!compareObjects(getPluginDescriptor(), other.getPluginDescriptor())) {
-                return false;
-            }
-
-            return compareObjects(getGoal(), other.getGoal());
+            return Objects.equals(getPluginDescriptor(), other.getPluginDescriptor())
+                    && Objects.equals(getGoal(), other.getGoal());
         }
 
         return false;
     }
 
-    private boolean compareObjects(Object first, Object second) {
-        if (first == second) {
-            return true;
-        }
-
-        if (first == null || second == null) {
-            return false;
-        }
-
-        return first.equals(second);
-    }
-
     /** {@inheritDoc} */
     public int hashCode() {
-        int result = 1;
-
-        String goal = getGoal();
-
-        if (goal != null) {
-            result += goal.hashCode();
-        }
-
-        PluginDescriptor pd = getPluginDescriptor();
-
-        if (pd != null) {
-            result -= pd.hashCode();
-        }
-
-        return result;
+        return Objects.hash(getGoal(), getPluginDescriptor());
     }
 
     /**

maven-plugin-api/src/test/java/org/apache/maven/plugin/descriptor/MojoDescriptorTest.java

@@ -0,0 +1,67 @@
+/*
+ * 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.
+ */
+package org.apache.maven.plugin.descriptor;
+
+/*
+ * 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.
+ */
+
+import junit.framework.TestCase;
+
+public class MojoDescriptorTest extends TestCase {
+
+    public void testGetParameterMap() throws DuplicateParameterException {
+        MojoDescriptor mojoDescriptor = new MojoDescriptor();
+        Parameter param1 = new Parameter();
+        param1.setName("param1");
+        param1.setDefaultValue("value1");
+        mojoDescriptor.addParameter(param1);
+
+        assertEquals(1, mojoDescriptor.getParameters().size());
+
+        assertEquals(
+                mojoDescriptor.getParameters().size(),
+                mojoDescriptor.getParameterMap().size());
+
+        Parameter param2 = new Parameter();
+        param2.setName("param2");
+        param2.setDefaultValue("value2");
+        mojoDescriptor.addParameter(param2);
+
+        assertEquals(2, mojoDescriptor.getParameters().size());
+        assertEquals(
+                mojoDescriptor.getParameters().size(),
+                mojoDescriptor.getParameterMap().size());
+    }
+}