Make parent level configurable for reference value in requirePropertyDiverges

src/main/java/org/codehaus/mojo/extraenforcer/model/RequirePropertyDiverges.java

@@ -66,6 +66,8 @@ public class RequirePropertyDiverges extends AbstractEnforcerRule {
      */
     private String regex = null;
 
+    private String reference = "DEFINING";
+
     private static final String RULE_NAME =
             StringUtils.lowercaseFirstLetter(RequirePropertyDiverges.class.getSimpleName());
 
@@ -89,13 +91,15 @@ public void execute() throws EnforcerRuleException {
         Object propValue = getPropertyValue();
         checkPropValueNotBlank(propValue);
 
+        ParentReference parentReference = getParentReference();
+
         getLog().debug(() -> getRuleName() + ": checking property '" + property + "' for project " + project);
 
-        final MavenProject parent = findDefiningParent(project);
+        final MavenProject parent = findParent(project, parentReference);
 
-        // fail fast if the defining parent could not be found due to a bug in the rule
+        // fail fast if the reference parent could not be found due to a bug in the rule
         if (parent == null) {
-            throw new IllegalStateException("Failed to find parent POM which defines the current rule");
+            throw new IllegalStateException("Failed to find reference POM which defines the current value");
         }
 
         if (project.equals(parent)) {
@@ -112,7 +116,7 @@ public void execute() throws EnforcerRuleException {
     }
 
     /**
-     * Checks the value of the project against the one given in the defining ancestor project.
+     * Checks the value of the project against the one given in the reference ancestor project.
      *
      * @param project
      * @param parent
@@ -153,6 +157,26 @@ void checkAgainstRegex(Object propValue) throws EnforcerRuleException {
         }
     }
 
+    /**
+     * Finds the ancestor project which defines the reference value.
+     *
+     * @param project to inspect
+     * @param reference project to diverge from
+     * @return the defining ancestor project.
+     */
+    final MavenProject findParent(final MavenProject project, ParentReference reference) {
+        switch (reference) {
+            case BASE:
+                return findBaseParent(project);
+            case DEFINING:
+                return findDefiningParent(project);
+            case PARENT:
+                return findDirectParent(project);
+            default:
+                throw new IllegalArgumentException("Unhandled ParentReference: " + reference.name());
+        }
+    }
+
     /**
      * Finds the ancestor project which defines the rule.
      *
@@ -176,6 +200,32 @@ final MavenProject findDefiningParent(final MavenProject project) {
         return parent;
     }
 
+    /**
+     * Finds the direct ancestor project.
+     *
+     * @param project to inspect
+     * @return the top-most local project or current project if it has no parent.
+     *
+     */
+    final MavenProject findDirectParent(MavenProject project) {
+        MavenProject parent = project.getParent();
+        return parent == null ? project : parent;
+    }
+
+    /**
+     * Finds the top-most local ancestor project.
+     *
+     * @param project to inspect
+     * @return the top-most local project.
+     */
+    final MavenProject findBaseParent(final MavenProject project) {
+        MavenProject current = project;
+        while (current.getParentFile() != null) {
+            current = project.getParent();
+        }
+        return current;
+    }
+
     /**
      * Creates a {@link Xpp3Dom} which corresponds to the configuration of the invocation.
      *
@@ -337,6 +387,31 @@ void checkPropValueNotBlank(Object propValue) throws EnforcerRuleException {
         }
     }
 
+    /**
+     * Extracted for easier testability.
+     *
+     * @return the ParentReference constant.
+     * @throws EnforcerRuleException if null or no ParentReference matches (case-insensitively)
+     */
+    ParentReference getParentReference() throws EnforcerRuleException {
+        return getParentReference(reference);
+    }
+
+    /**
+     * Extracted for easier testability.
+     *
+     * @param parentReferenceName name of the ParentReference.
+     * @return the ParentReference enum constant.
+     * @throws EnforcerRuleException if null or no ParentReference matches (case-insensitively)
+     */
+    ParentReference getParentReference(String parentReferenceName) throws EnforcerRuleException {
+        try {
+            return ParentReference.valueOf(StringUtils.upperCase(StringUtils.strip(parentReferenceName)));
+        } catch (IllegalArgumentException iae) {
+            throw new EnforcerRuleError("Unknown parent reference value: " + parentReferenceName, iae);
+        }
+    }
+
     /**
      * Either return the submitted errorMessage or replace it with the custom message set in the rule extended
      * by the property name.
@@ -375,6 +450,13 @@ void setMessage(String message) {
         this.message = message;
     }
 
+    /**
+     * @param reference the reference to set
+     */
+    void setReference(String reference) {
+        this.reference = reference;
+    }
+
     /**
      * Creates the DOM of the invoking rule, but returns the children alphabetically sorted.
      */
@@ -416,4 +498,19 @@ private void addChildrenToRuleDom() {
             }
         }
     }
+
+    enum ParentReference {
+        /**
+         * The top-most local project (i.e.: the highest parent whose POM does not come from a repository)
+         */
+        BASE,
+        /**
+         * The parent where the current requirePropertyDiverges rule is defined
+         */
+        DEFINING,
+        /**
+         * The immediate parent (same as ${project.parent})
+         */
+        PARENT
+    }
 }

src/site/apt/requirePropertyDiverges.apt.vm

@@ -40,14 +40,22 @@ Require Property Diverges
 
    * <<property>> - name of the property which should diverge. Must be given.
 
+   * <<reference>> - parent level to use as evaluation context for the reference value:
+
+      * DEFINING - the rule-defining POM. Default historical behaviour.
+
+      * PARENT - the direct parent of the current POM. The rule is skipped if the POM has no parent.
+
+      * BASE - the top-most local POM of the project. The rule is skipped if the current POM is the top-most POM.
+
    * <<regex>> - match the property value to a given regular expression.
    When not given, this rule checks that the property in the child does not equal
    the one from the defining ancestor. 
 
    []
 
   Note that certain properties (e.g. <<<project.url>>> or <<<project.scm.connection>>>
-  are automatically extended with the child's <<<project.artifactId>>>, so using
+  are automatically extended with the child's <<<project.artifactId>>> (see {{{https://maven.apache.org/ref/current/maven-model-builder/#inheritance-assembly}Inheritance assembly}}), so using
   a regex will help in this case, see sample below.
 
   Another caveat: properties defined in the <<<properties>>> section will be 

src/test/java/org/codehaus/mojo/extraenforcer/model/RequirePropertyDivergesTest.java

@@ -19,6 +19,8 @@
  * under the License.
  */
 
+import java.io.File;
+
 import org.apache.maven.enforcer.rule.api.EnforcerLogger;
 import org.apache.maven.enforcer.rule.api.EnforcerRuleException;
 import org.apache.maven.model.Build;
@@ -222,6 +224,87 @@ public void testCheckAgainstParentValue() throws EnforcerRuleException, Expressi
         testCheckAgainstParentValue("company.parent-pom", "company.project1");
     }
 
+    @Test(expected = NullPointerException.class)
+    public void testGetParentReferenceNull() throws EnforcerRuleException {
+        RequirePropertyDiverges instance = createMockRule(mock(MavenProject.class));
+        instance.getParentReference(null);
+    }
+
+    @Test(expected = EnforcerRuleException.class)
+    public void testGetParentReferenceEmpty() throws EnforcerRuleException {
+        RequirePropertyDiverges instance = createMockRule(mock(MavenProject.class));
+        instance.getParentReference("");
+    }
+
+    @Test
+    public void testGetParentReferenceKnownValues() throws EnforcerRuleException {
+        RequirePropertyDiverges instance = createMockRule(mock(MavenProject.class));
+        assertEquals(RequirePropertyDiverges.ParentReference.BASE, instance.getParentReference("BaSE"));
+        assertEquals(RequirePropertyDiverges.ParentReference.DEFINING, instance.getParentReference("Defining"));
+        assertEquals(RequirePropertyDiverges.ParentReference.PARENT, instance.getParentReference("PaRenT"));
+    }
+
+    @Test(expected = EnforcerRuleException.class)
+    public void testGetParentReferenceUnknownValue() throws EnforcerRuleException {
+        RequirePropertyDiverges instance = createMockRule(mock(MavenProject.class));
+        instance.getParentReference("BOGUS");
+    }
+
+    @Test
+    public void testGetParentReferenceDefault() throws EnforcerRuleException {
+        RequirePropertyDiverges instance = createMockRule(mock(MavenProject.class));
+        assertEquals(RequirePropertyDiverges.ParentReference.DEFINING, instance.getParentReference());
+    }
+
+    @Test
+    public void testFindParentDefining() throws EnforcerRuleException {
+        RequirePropertyDiverges instance = createMockRule(mock(MavenProject.class));
+        MavenProject root = createParentProject();
+        MavenProject base = createMavenProject("company", "main-pom");
+        MavenProject child = createMavenProject("company", "child");
+        child.setParent(base);
+        base.setParent(root);
+        // Rule is defined in "root", expect root always
+        assertEquals(root, instance.findParent(root, RequirePropertyDiverges.ParentReference.DEFINING));
+        assertEquals(root, instance.findParent(base, RequirePropertyDiverges.ParentReference.DEFINING));
+        assertEquals(root, instance.findParent(child, RequirePropertyDiverges.ParentReference.DEFINING));
+    }
+
+    @Test
+    public void testFindParentParent() throws EnforcerRuleException {
+        RequirePropertyDiverges instance = createMockRule(mock(MavenProject.class));
+        MavenProject root = createParentProject();
+        MavenProject base = createMavenProject("company", "main-pom");
+        MavenProject child = createMavenProject("company", "child");
+        child.setParent(base);
+        base.setParent(root);
+        // "root" has no parent, expect root (self)
+        assertEquals(root, instance.findParent(root, RequirePropertyDiverges.ParentReference.PARENT));
+        // base's parent is root, expect root
+        assertEquals(root, instance.findParent(base, RequirePropertyDiverges.ParentReference.PARENT));
+        // child's parent is base, expect base
+        assertEquals(base, instance.findParent(child, RequirePropertyDiverges.ParentReference.PARENT));
+    }
+
+    @Test
+    public void testFindParentBase() throws EnforcerRuleException {
+        RequirePropertyDiverges instance = createMockRule(mock(MavenProject.class));
+        MavenProject root = createParentProject();
+        MavenProject base = createMavenProject("company", "main-pom");
+        base.setParentFile(null);
+        MavenProject child = createMavenProject("company", "child");
+        child.setParent(base);
+        child.setParentFile(mock(File.class));
+        base.setParent(root);
+
+        // "root" is not local, expect root (self)
+        assertEquals(root, instance.findParent(root, RequirePropertyDiverges.ParentReference.BASE));
+        // base is the top-most local (has no parentFile), expect base (self)
+        assertEquals(base, instance.findParent(base, RequirePropertyDiverges.ParentReference.BASE));
+        // child has a local parent, expect base
+        assertEquals(base, instance.findParent(child, RequirePropertyDiverges.ParentReference.BASE));
+    }
+
     void testCheckAgainstParentValue(final String parentGroupId, final String childGroupId)
             throws ExpressionEvaluationException, EnforcerRuleException {
         MavenProject project = createMavenProject(childGroupId, "child");
@@ -251,7 +334,7 @@ static MavenProject createMavenProject(final String groupId, final String artifa
     }
 
     void setUpHelper(final MavenProject project, final String propertyValue) throws RuntimeException {
-        //            when(helper.evaluate("${project}")).thenReturn(project);
+        // when(helper.evaluate("${project}")).thenReturn(project);
         try {
             when(evaluator.evaluate("${checkedProperty}")).thenReturn(propertyValue);
         } catch (ExpressionEvaluationException e) {