[MSHADE-382] Add property to skip execution

* added a skip field to ShadeMojo

Co-authored-by: Markus Karg <markus@headcrashing.eu>

src/it/projects/MSHADE-382_skip_execution/invoker.properties

@@ -0,0 +1,18 @@
+# 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.java.version = 1.8+

src/it/projects/MSHADE-382_skip_execution/pom.xml

@@ -0,0 +1,55 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!--
+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>
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.apache.maven.its.shade.mj</groupId>
+  <artifactId>skip-execution</artifactId>
+  <version>1.0</version>
+
+  <name>MSHADE-382</name>
+  <description>
+    Skip shading
+  </description>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-shade-plugin</artifactId>
+        <version>@project.version@</version>
+        <executions>
+          <execution>
+            <id>create-shaded-artifact</id>
+            <phase>package</phase>
+            <goals>
+              <goal>shade</goal>
+            </goals>
+            <configuration>
+              <skip>true</skip>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/projects/MSHADE-382_skip_execution/verify.groovy

@@ -0,0 +1,20 @@
+/*
+ * 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, "target/original-skip-execution-1.0.jar" ).exists()) : "Shading was not skipped."

src/main/java/org/apache/maven/plugins/shade/mojo/ShadeMojo.java

@@ -385,12 +385,24 @@ public class ShadeMojo
     @Inject
     private Map<String, Shader> shaders;
 
+    /**
+     * When true, skips the execution of this MOJO.
+     * @since 3.3.0
+     */
+    @Parameter( defaultValue = "false" )
+    private boolean skip;
+
     /**
      * @throws MojoExecutionException in case of an error.
      */
     public void execute()
         throws MojoExecutionException
     {
+        if ( skip )
+        {
+            getLog().info( "Shading has been skipped." );
+            return;
+        }
 
         setupHintedShader();