Add support for POM mixins

.mvn/maven.config

@@ -1,2 +1 @@
-# A hack to pass on this property for Maven 3 as well; Maven 4 supports this property out of the box
 -DsessionRootDirectory=${session.rootDirectory}

api/maven-api-core/src/main/java/org/apache/maven/api/services/ModelBuilder.java

@@ -29,7 +29,9 @@ public interface ModelBuilder extends Service {
 
     String MODEL_VERSION_4_1_0 = "4.1.0";
 
-    List<String> KNOWN_MODEL_VERSIONS = List.of(MODEL_VERSION_4_0_0, MODEL_VERSION_4_1_0);
+    String MODEL_VERSION_4_2_0 = "4.2.0";
+
+    List<String> KNOWN_MODEL_VERSIONS = List.of(MODEL_VERSION_4_0_0, MODEL_VERSION_4_1_0, MODEL_VERSION_4_2_0);
 
     ModelBuilderSession newSession();
 

api/maven-api-core/src/main/java/org/apache/maven/api/services/ModelProblem.java

@@ -66,7 +66,12 @@ enum Version {
         /**
          * Validation for Maven 4.1 POM format.
          */
-        V41
+        V41,
+
+        /**
+         * Validation for Maven 4.2 POM format.
+         */
+        V42
     }
 
     /**

api/maven-api-model/pom.xml

@@ -48,7 +48,7 @@ under the License.
         <groupId>org.codehaus.modello</groupId>
         <artifactId>modello-maven-plugin</artifactId>
         <configuration>
-          <version>4.1.0</version>
+          <version>4.2.0</version>
           <velocityBasedir>${project.basedir}/../../src/mdo</velocityBasedir>
           <models>
             <model>src/main/mdo/maven.mdo</model>

api/maven-api-model/src/main/mdo/maven.mdo

@@ -111,6 +111,20 @@
           </association>
         </field>
 
+        <!-- ====================================================================== -->
+        <!-- Mixins                                                                 -->
+        <!-- ====================================================================== -->
+
+        <field xdoc.separator="blank">
+          <name>mixins</name>
+          <version>4.2.0+</version>
+          <description>Mixins...</description>
+          <association>
+            <type>Mixin</type>
+            <multiplicity>*</multiplicity>
+          </association>
+        </field>
+
         <!-- ====================================================================== -->
         <!-- groupId/artifactId/Version/Packaging                                   -->
         <!-- ====================================================================== -->
@@ -526,7 +540,7 @@
       <fields>
         <field xdoc.separator="blank">
           <name>modules</name>
-          <version>4.0.0/4.1.0</version>
+          <version>4.0.0/4.2.0</version>
           <description>
             @deprecated Use {@link #subprojects} instead.
           </description>
@@ -540,7 +554,7 @@
         </field>
         <field xdoc.separator="blank">
           <name>subprojects</name>
-          <version>4.1.0</version>
+          <version>4.1.0+</version>
           <description>The subprojects (formerly called modules) to build as a part of this
             project. Each subproject listed is a relative path to the directory containing the subproject.
             To be consistent with the way default URLs are calculated from parent, it is recommended
@@ -1836,6 +1850,23 @@
       </codeSegments>
 
     </class>
+    <class>
+        <name>Mixin</name>
+        <version>4.1.0+</version>
+        <superClass>Parent</superClass>
+        <fields>
+            <field>
+                <name>classifier</name>
+                <version>4.1.0+</version>
+                <type>String</type>
+            </field>
+            <field>
+                <name>extension</name>
+                <version>4.1.0+</version>
+                <type>String</type>
+            </field>
+        </fields>
+    </class>
     <class>
       <name>Scm</name>
       <version>4.0.0+</version>

compat/maven-model-builder/src/main/java/org/apache/maven/model/building/FileToRawModelMerger.java

@@ -138,6 +138,12 @@ protected void mergeModel_Profiles(
                 .collect(Collectors.toList()));
     }
 
+    @Override
+    protected void mergeModel_Mixins(
+            Model.Builder builder, Model target, Model source, boolean sourceDominant, Map<Object, Object> context) {
+        // don't merge
+    }
+
     @Override
     protected void mergeModelBase_Dependencies(
             ModelBase.Builder builder,

compat/maven-model-builder/src/main/resources/org/apache/maven/model/pom-4.1.0.xml

@@ -20,8 +20,10 @@ under the License.
 -->
 
 <!-- START SNIPPET: superpom -->
-<project>
-  <modelVersion>4.0.0</modelVersion>
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+  <modelVersion>4.1.0</modelVersion>
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

compat/maven-model-builder/src/main/resources/org/apache/maven/model/pom-4.2.0.xml

@@ -0,0 +1,68 @@
+<?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.
+-->
+
+<!-- START SNIPPET: superpom -->
+<project xmlns="http://maven.apache.org/POM/4.2.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.2.0 https://maven.apache.org/xsd/maven-4.2.0.xsd">
+  <modelVersion>4.2.0</modelVersion>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
+    <!-- Fixed date for reproducible build -->
+    <project.build.outputTimestamp>1980-02-01T00:00:00Z</project.build.outputTimestamp>
+  </properties>
+
+  <build>
+    <directory>${project.basedir}/target</directory>
+    <outputDirectory>${project.build.directory}/classes</outputDirectory>
+    <finalName>${project.artifactId}-${project.version}</finalName>
+    <testOutputDirectory>${project.build.directory}/test-classes</testOutputDirectory>
+    <sourceDirectory>${project.basedir}/src/main/java</sourceDirectory>
+    <scriptSourceDirectory>${project.basedir}/src/main/scripts</scriptSourceDirectory>
+    <testSourceDirectory>${project.basedir}/src/test/java</testSourceDirectory>
+    <resources>
+      <resource>
+        <directory>${project.basedir}/src/main/resources</directory>
+      </resource>
+      <resource>
+        <directory>${project.basedir}/src/main/resources-filtered</directory>
+        <filtering>true</filtering>
+      </resource>
+    </resources>
+    <testResources>
+      <testResource>
+        <directory>${project.basedir}/src/test/resources</directory>
+      </testResource>
+      <testResource>
+        <directory>${project.basedir}/src/test/resources-filtered</directory>
+        <filtering>true</filtering>
+      </testResource>
+    </testResources>
+  </build>
+
+  <reporting>
+    <outputDirectory>${project.build.directory}/site</outputDirectory>
+  </reporting>
+
+</project>
+<!-- END SNIPPET: superpom -->

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvnup/goals/ModelUpgradeStrategy.java

@@ -37,8 +37,10 @@
 import static org.apache.maven.cling.invoker.mvnup.goals.ModelVersionUtils.getSchemaLocationForModelVersion;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.ModelVersions.MODEL_VERSION_4_0_0;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.ModelVersions.MODEL_VERSION_4_1_0;
+import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.ModelVersions.MODEL_VERSION_4_2_0;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.Namespaces.MAVEN_4_0_0_NAMESPACE;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.Namespaces.MAVEN_4_1_0_NAMESPACE;
+import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.Namespaces.MAVEN_4_2_0_NAMESPACE;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.XmlAttributes.SCHEMA_LOCATION;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.XmlAttributes.XSI_NAMESPACE_PREFIX;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.XmlAttributes.XSI_NAMESPACE_URI;
@@ -246,7 +248,9 @@ private String determineTargetModelVersion(UpgradeContext context) {
      * Gets the namespace URI for a model version.
      */
     private String getNamespaceForModelVersion(String modelVersion) {
-        if (MODEL_VERSION_4_1_0.equals(modelVersion)) {
+        if (MODEL_VERSION_4_2_0.equals(modelVersion)) {
+            return MAVEN_4_2_0_NAMESPACE;
+        } else if (MODEL_VERSION_4_1_0.equals(modelVersion)) {
             return MAVEN_4_1_0_NAMESPACE;
         } else {
             return MAVEN_4_0_0_NAMESPACE;

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvnup/goals/ModelVersionUtils.java

@@ -24,9 +24,12 @@
 
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.ModelVersions.MODEL_VERSION_4_0_0;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.ModelVersions.MODEL_VERSION_4_1_0;
+import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.ModelVersions.MODEL_VERSION_4_2_0;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.Namespaces.MAVEN_4_0_0_NAMESPACE;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.Namespaces.MAVEN_4_1_0_NAMESPACE;
+import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.Namespaces.MAVEN_4_2_0_NAMESPACE;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.SchemaLocations.MAVEN_4_1_0_SCHEMA_LOCATION;
+import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.SchemaLocations.MAVEN_4_2_0_SCHEMA_LOCATION;
 import static org.apache.maven.cling.invoker.mvnup.goals.UpgradeConstants.XmlElements.MODEL_VERSION;
 
 /**
@@ -60,7 +63,9 @@ public static String detectModelVersion(Document pomDocument) {
 
         // Fallback to namespace URI detection
         String namespaceUri = namespace.getURI();
-        if (MAVEN_4_1_0_NAMESPACE.equals(namespaceUri)) {
+        if (MAVEN_4_2_0_NAMESPACE.equals(namespaceUri)) {
+            return MODEL_VERSION_4_2_0;
+        } else if (MAVEN_4_1_0_NAMESPACE.equals(namespaceUri)) {
             return MODEL_VERSION_4_1_0;
         } else if (MAVEN_4_0_0_NAMESPACE.equals(namespaceUri)) {
             return MODEL_VERSION_4_0_0;
@@ -72,13 +77,15 @@ public static String detectModelVersion(Document pomDocument) {
 
     /**
      * Checks if a model version is valid for upgrade operations.
-     * Currently only supports 4.0.0 and 4.1.0.
+     * Currently supports 4.0.0, 4.1.0, and 4.2.0.
      *
      * @param modelVersion the model version to validate
      * @return true if the model version is valid
      */
     public static boolean isValidModelVersion(String modelVersion) {
-        return MODEL_VERSION_4_0_0.equals(modelVersion) || MODEL_VERSION_4_1_0.equals(modelVersion);
+        return MODEL_VERSION_4_0_0.equals(modelVersion)
+                || MODEL_VERSION_4_1_0.equals(modelVersion)
+                || MODEL_VERSION_4_2_0.equals(modelVersion);
     }
 
     /**
@@ -93,8 +100,15 @@ public static boolean canUpgrade(String fromVersion, String toVersion) {
             return false;
         }
 
-        // Currently only support 4.0.0 → 4.1.0 upgrade
-        return MODEL_VERSION_4_0_0.equals(fromVersion) && MODEL_VERSION_4_1_0.equals(toVersion);
+        // Support upgrades: 4.0.0 → 4.1.0, 4.0.0 → 4.2.0, 4.1.0 → 4.2.0
+        if (MODEL_VERSION_4_0_0.equals(fromVersion)) {
+            return MODEL_VERSION_4_1_0.equals(toVersion) || MODEL_VERSION_4_2_0.equals(toVersion);
+        }
+        if (MODEL_VERSION_4_1_0.equals(fromVersion)) {
+            return MODEL_VERSION_4_2_0.equals(toVersion);
+        }
+
+        return false;
     }
 
     /**
@@ -105,7 +119,9 @@ public static boolean canUpgrade(String fromVersion, String toVersion) {
      * @return true if eligible for inference
      */
     public static boolean isEligibleForInference(String modelVersion) {
-        return MODEL_VERSION_4_0_0.equals(modelVersion) || MODEL_VERSION_4_1_0.equals(modelVersion);
+        return MODEL_VERSION_4_0_0.equals(modelVersion)
+                || MODEL_VERSION_4_1_0.equals(modelVersion)
+                || MODEL_VERSION_4_2_0.equals(modelVersion);
     }
 
     /**
@@ -220,8 +236,13 @@ public static boolean removeModelVersion(Document pomDocument) {
      * @return the schema location
      */
     public static String getSchemaLocationForModelVersion(String modelVersion) {
-        if (MODEL_VERSION_4_1_0.equals(modelVersion) || isNewerThan410(modelVersion)) {
+        if (MODEL_VERSION_4_2_0.equals(modelVersion)) {
+            return MAVEN_4_2_0_SCHEMA_LOCATION;
+        } else if (MODEL_VERSION_4_1_0.equals(modelVersion)) {
             return MAVEN_4_1_0_SCHEMA_LOCATION;
+        } else if (isNewerThan410(modelVersion)) {
+            // For versions newer than 4.1.0 but not specifically 4.2.0, use 4.2.0 schema
+            return MAVEN_4_2_0_SCHEMA_LOCATION;
         }
         return UpgradeConstants.SchemaLocations.MAVEN_4_0_0_SCHEMA_LOCATION;
     }

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvnup/goals/UpgradeConstants.java

@@ -38,6 +38,9 @@ public static final class ModelVersions {
         /** Maven 4.1.0 model version */
         public static final String MODEL_VERSION_4_1_0 = "4.1.0";
 
+        /** Maven 4.2.0 model version */
+        public static final String MODEL_VERSION_4_2_0 = "4.2.0";
+
         private ModelVersions() {
             // Utility class
         }
@@ -183,6 +186,9 @@ public static final class Namespaces {
         /** Maven 4.1.0 namespace URI */
         public static final String MAVEN_4_1_0_NAMESPACE = "http://maven.apache.org/POM/4.1.0";
 
+        /** Maven 4.2.0 namespace URI */
+        public static final String MAVEN_4_2_0_NAMESPACE = "http://maven.apache.org/POM/4.2.0";
+
         private Namespaces() {
             // Utility class
         }
@@ -200,6 +206,10 @@ public static final class SchemaLocations {
         public static final String MAVEN_4_1_0_SCHEMA_LOCATION =
                 Namespaces.MAVEN_4_1_0_NAMESPACE + " https://maven.apache.org/xsd/maven-4.1.0.xsd";
 
+        /** Schema location for 4.2.0 models */
+        public static final String MAVEN_4_2_0_SCHEMA_LOCATION =
+                Namespaces.MAVEN_4_2_0_NAMESPACE + " https://maven.apache.org/xsd/maven-4.2.0.xsd";
+
         private SchemaLocations() {
             // Utility class
         }

impl/maven-cli/src/test/java/org/apache/maven/cling/invoker/mvnup/goals/ModelVersionUtilsTest.java

@@ -129,14 +129,14 @@ void shouldDetectVersionFromNamespaceWhenModelVersionMissing() throws Exception
     class ModelVersionValidationTests {
 
         @ParameterizedTest
-        @ValueSource(strings = {"4.0.0", "4.1.0"})
+        @ValueSource(strings = {"4.0.0", "4.1.0", "4.2.0"})
         @DisplayName("should validate supported model versions")
         void shouldValidateSupportedModelVersions(String version) {
             assertTrue(ModelVersionUtils.isValidModelVersion(version));
         }
 
         @ParameterizedTest
-        @ValueSource(strings = {"3.0.0", "5.0.0", "4.2.0", "2.0.0", "6.0.0"})
+        @ValueSource(strings = {"3.0.0", "5.0.0", "2.0.0", "6.0.0"})
         @DisplayName("should reject unsupported model versions")
         void shouldRejectUnsupportedModelVersions(String version) {
             assertFalse(ModelVersionUtils.isValidModelVersion(version));
@@ -381,11 +381,11 @@ void shouldGetSchemaLocationFor400() {
         @DisplayName("should handle unknown model version in schema location")
         void shouldHandleUnknownModelVersionInSchemaLocation() {
             String schemaLocation = ModelVersionUtils.getSchemaLocationForModelVersion("5.0.0");
-            assertNotNull(schemaLocation); // Should return 4.1.0 schema for newer versions
-            // The method returns the 4.1.0 schema location for versions newer than 4.1.0
+            assertNotNull(schemaLocation); // Should return 4.2.0 schema for newer versions
+            // The method returns the 4.2.0 schema location for versions newer than 4.1.0
             assertTrue(
-                    schemaLocation.contains("4.1.0"),
-                    "Expected schema location to contain '4.1.0', but was: " + schemaLocation);
+                    schemaLocation.contains("4.2.0"),
+                    "Expected schema location to contain '4.2.0', but was: " + schemaLocation);
         }
     }
 

impl/maven-core/src/main/java/org/apache/maven/internal/transformation/impl/DefaultConsumerPomBuilder.java

@@ -209,6 +209,7 @@ static Model transformNonPom(Model model, MavenProject project) {
                                 .preserveModelVersion(false)
                                 .root(false)
                                 .parent(null)
+                                .mixins(null)
                                 .build(null),
                         model)
                 .mailingLists(null)