[MENFORCER-422] Added externalRules rule

.gitignore

@@ -6,4 +6,4 @@ target
 .svn
 *.iml
 .checkstyle
-
+.DS_Store

enforcer-rules/src/main/java/org/apache/maven/plugins/enforcer/EnforcerDescriptor.java

@@ -0,0 +1,42 @@
+package org.apache.maven.plugins.enforcer;
+
+/*
+ * 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 org.apache.maven.enforcer.rule.api.EnforcerRule;
+
+/**
+ * An enforcer rules descriptor used by {@link ExternalRules}
+ *
+ * @author <a href="mailto:gastaldi@apache.org">George Gastaldi</a>
+ */
+public class EnforcerDescriptor
+{
+    EnforcerRule[] rules;
+
+    public EnforcerRule[] getRules()
+    {
+        return rules;
+    }
+
+    public void setRules( EnforcerRule[] rules )
+    {
+        this.rules = rules;
+    }
+}

enforcer-rules/src/main/java/org/apache/maven/plugins/enforcer/ExternalRules.java

@@ -0,0 +1,152 @@
+package org.apache.maven.plugins.enforcer;
+
+/*
+ * 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 org.apache.maven.enforcer.rule.api.EnforcerRule;
+import org.apache.maven.enforcer.rule.api.EnforcerRuleException;
+import org.apache.maven.enforcer.rule.api.EnforcerRuleHelper;
+import org.apache.maven.plugin.MojoExecution;
+import org.codehaus.plexus.classworlds.realm.ClassRealm;
+import org.codehaus.plexus.component.configurator.ComponentConfigurator;
+import org.codehaus.plexus.component.repository.exception.ComponentLookupException;
+import org.codehaus.plexus.configuration.PlexusConfiguration;
+import org.codehaus.plexus.configuration.xml.XmlPlexusConfiguration;
+import org.codehaus.plexus.util.xml.Xpp3DomBuilder;
+import org.codehaus.plexus.util.xml.pull.XmlPullParserException;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Files;
+
+/**
+ * An enforcer rule that will invoke rules from an external resource
+ *
+ * @author <a href="mailto:gastaldi@apache.org">George Gastaldi</a>
+ */
+public class ExternalRules extends AbstractNonCacheableEnforcerRule
+{
+    private static final String LOCATION_PREFIX_CLASSPATH = "classpath:";
+
+    /**
+     * The external rules location. If it starts with "classpath:", the resource is read from the classpath.
+     * Otherwise, it is handled as a filesystem path, either absolute, or relative to <code>${project.basedir}</code>
+     */
+    String location;
+
+    public ExternalRules()
+    {
+    }
+
+    public ExternalRules( String location )
+    {
+        this.location = location;
+    }
+
+    @Override
+    public void execute( EnforcerRuleHelper helper ) throws EnforcerRuleException
+    {
+        // Find descriptor
+        EnforcerDescriptor enforcerDescriptor = getEnforcerDescriptor( helper );
+        for ( EnforcerRule rule : enforcerDescriptor.getRules() )
+        {
+            rule.execute( helper );
+        }
+    }
+
+    /**
+     * Resolve the {@link EnforcerDescriptor} based on the provided {@link #descriptor} or {@link #descriptorRef}
+     *
+     * @param helper used to build the {@link EnforcerDescriptor}
+     * @return an {@link EnforcerDescriptor} for this rule
+     * @throws EnforcerRuleException if any failure happens while reading the descriptor
+     */
+    EnforcerDescriptor getEnforcerDescriptor( EnforcerRuleHelper helper )
+            throws EnforcerRuleException
+    {
+        try ( InputStream descriptorStream = resolveDescriptor( helper ) )
+        {
+            EnforcerDescriptor descriptor = new EnforcerDescriptor();
+            // To get configuration from the enforcer-plugin mojo do:
+            //helper.evaluate(helper.getComponent(MojoExecution.class).getConfiguration().getChild("fail").getValue())
+            // Configure EnforcerDescriptor from the XML
+            ComponentConfigurator configurator = helper.getComponent( ComponentConfigurator.class, "basic" );
+            configurator.configureComponent( descriptor, toPlexusConfiguration( descriptorStream ), helper,
+                    getClassRealm( helper ) );
+            return descriptor;
+        }
+        catch ( EnforcerRuleException e )
+        {
+            throw e;
+        }
+        catch ( Exception e )
+        {
+            throw new EnforcerRuleException( "Error while enforcing rules", e );
+        }
+    }
+
+    private InputStream resolveDescriptor( EnforcerRuleHelper helper )
+            throws ComponentLookupException, EnforcerRuleException
+    {
+        InputStream descriptorStream;
+        if ( location != null )
+        {
+            if ( location.startsWith( LOCATION_PREFIX_CLASSPATH ) )
+            {
+                String classpathLocation = location.substring( LOCATION_PREFIX_CLASSPATH.length() );
+                ClassLoader classRealm = getClassRealm( helper );
+                descriptorStream = classRealm.getResourceAsStream( classpathLocation );
+                if ( descriptorStream == null )
+                {
+                    throw new EnforcerRuleException( "Location '" + classpathLocation + "' not found in classpath" );
+                }
+            }
+            else
+            {
+                File descriptorFile = helper.alignToBaseDirectory( new File( location ) );
+                try
+                {
+                    descriptorStream = Files.newInputStream( descriptorFile.toPath() );
+                }
+                catch ( IOException e )
+                {
+                    throw new EnforcerRuleException( "Could not read descriptor in " + descriptorFile, e );
+                }
+            }
+        }
+        else
+        {
+            throw new EnforcerRuleException( "No location provided" );
+        }
+        return descriptorStream;
+    }
+
+    private static PlexusConfiguration toPlexusConfiguration( InputStream descriptorStream )
+            throws XmlPullParserException, IOException
+    {
+        return new XmlPlexusConfiguration( Xpp3DomBuilder.build( descriptorStream, "UTF-8" ) );
+    }
+
+    private ClassRealm getClassRealm( EnforcerRuleHelper helper ) throws ComponentLookupException
+    {
+        return helper.getComponent( MojoExecution.class ).getMojoDescriptor().getRealm();
+    }
+
+}

enforcer-rules/src/site/apt/externalRules.apt.vm

@@ -0,0 +1,100 @@
+~~ 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.
+
+  ------
+  External Rules
+  ------
+  George Gastaldi
+  ------
+  2022-08-17
+  ------
+
+External Rules
+
+    This rule will evaluate rules from an external resource. It can be a classpath resource present in a <<<maven-enforcer-plugin>>> dependency or a local file.
+
+
+    Sample Plugin Configuration:
+
++---+
+<project>
+    [...]
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-enforcer-plugin</artifactId>
+                <version>${project.version}</version>
+                <dependencies>
+                    <!-- Dependency containing the enforcer/rules.xml file -->
+                    <dependency>
+                        <groupId>org.foo</groupId>
+                        <artifactId>foobar-rules</artifactId>
+                        <version>1.0.0</version>
+                    </dependency>
+                </dependencies>
+                <executions>
+                    <execution>
+                        <id>enforce</id>
+                        <goals>
+                            <goal>enforce</goal>
+                        </goals>
+                        <configuration>
+                            <rules>
+                                <ExternalRules>
+                                    <!-- enforcer/rules.xml is supposed to be a classpath resource present -->
+                                    <!-- in org.foo:foobar-rules dependency of maven-enforcer-plugin defined above -->
+                                    <location>classpath:enforcer/rules.xml</location>
+                                </ExternalRules>
+                                <ExternalRules>
+                                    <!-- You can add multiple <ExternalRules> elements if you need to enforce -->
+                                    <!-- rules from multiple resources. -->
+                                    <!-- src/build/rules.xml is a local file path relative to ${project.basedir} -->
+                                    <location>src/build/rules.xml</location>
+                                </ExternalRules>
+                            </rules>
+                            <fail>true</fail>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+    [...]
+</project>
++---+
+
+
+The External Enforcer Rule Descriptor
+
+    Here is a sample rules file. The rules element expects the same content as in the {{{https://maven.apache.org/enforcer/maven-enforcer-plugin/enforce-mojo.html#rules}Enforcer Mojo rules configuration}}:
+
++---+
+<enforcer>
+    <rules>
+        <dependencyConvergence/>
+        <bannedDependencies>
+            <excludes>
+                <exclude>org.jboss.spec.javax.annotation:jboss-annotations-api_1.2_spec</exclude>
+            </excludes>
+            <includes>
+                <include>jakarta.xml.bind:jakarta.xml.bind-api:*:*:test</include>
+            </includes>
+        </bannedDependencies>
+    </rules>
+</enforcer>
++---+

enforcer-rules/src/site/apt/index.apt

@@ -49,6 +49,8 @@ Built-In Rules
 
   * {{{./evaluateBeanshell.html}evaluateBeanshell}} - evaluates a beanshell script.
 
+  * {{{./externalRules.html}externalRules}} - evaluate rules from an external resource.
+
   * {{{./reactorModuleConvergence.html}reactorModuleConvergence}} - enforces that a multi module build follows best practice.
 
   * {{{./requireActiveProfile.html}requireActiveProfile}} - enforces one or more active profiles.

enforcer-rules/src/test/java/org/apache/maven/plugins/enforcer/EnforcerTestUtils.java

@@ -38,13 +38,15 @@
 import org.apache.maven.model.Plugin;
 import org.apache.maven.plugin.MojoExecution;
 import org.apache.maven.plugin.PluginParameterExpressionEvaluator;
+import org.apache.maven.plugin.descriptor.MojoDescriptor;
 import org.apache.maven.plugin.logging.SystemStreamLog;
 import org.apache.maven.plugins.enforcer.utils.MockEnforcerExpressionEvaluator;
 import org.apache.maven.project.MavenProject;
 import org.apache.maven.project.ProjectBuildingRequest;
 import org.apache.maven.shared.dependency.graph.DependencyCollectorBuilder;
 import org.apache.maven.shared.dependency.graph.internal.DefaultDependencyNode;
 import org.codehaus.plexus.PlexusContainer;
+import org.codehaus.plexus.classworlds.ClassWorld;
 import org.codehaus.plexus.component.configurator.expression.ExpressionEvaluator;
 import org.codehaus.plexus.component.repository.exception.ComponentLookupException;
 import org.mockito.Mockito;
@@ -121,14 +123,14 @@ public static EnforcerRuleHelper getHelper( MavenProject project )
     public static EnforcerRuleHelper getHelper( MavenProject project, boolean mockExpression )
     {
         MavenSession session = getMavenSession();
+        MojoExecution mockExecution = mock( MojoExecution.class );
         ExpressionEvaluator eval;
         if ( mockExpression )
         {
             eval = new MockEnforcerExpressionEvaluator( session );
         }
         else
         {
-            MojoExecution mockExecution = mock( MojoExecution.class );
             session.setCurrentProject( project );
             eval = new PluginParameterExpressionEvaluator( session, mockExecution );
         }
@@ -154,6 +156,18 @@ public static EnforcerRuleHelper getHelper( MavenProject project, boolean mockEx
         {
             // test will fail
         }
+        ClassWorld classWorld = new ClassWorld( "test", EnforcerTestUtils.class.getClassLoader() );
+        MojoDescriptor mojoDescriptor = new MojoDescriptor();
+        mojoDescriptor.setRealm( classWorld.getClassRealm( "test" ) );
+        when( mockExecution.getMojoDescriptor() ).thenReturn( mojoDescriptor );
+        try
+        {
+            when( container.lookup( MojoExecution.class ) ).thenReturn( mockExecution );
+        }
+        catch ( ComponentLookupException e )
+        {
+            // test will fail
+        }
         return new DefaultEnforcementRuleHelper( session, eval, new SystemStreamLog(), container );
     }