[MNG-11133] Fix mixin property precedence - mixins should override parent properties

impl/maven-impl/src/main/java/org/apache/maven/impl/model/DefaultModelBuilder.java

@@ -1423,7 +1423,14 @@ private Model readEffectiveModel() throws ModelBuilderException {
             // Mixins
             for (Mixin mixin : model.getMixins()) {
                 Model parent = resolveParent(model, mixin, profileActivationContext, parentChain);
+                // Merge mixin into model
                 model = inheritanceAssembler.assembleModelInheritance(model, parent, request, this);
+                // Ensure mixin properties override any previously inherited properties
+                // This is necessary because normal inheritance gives child precedence, but for mixins
+                // we want the mixin to take precedence over inherited parent properties
+                Map<String, String> mergedProperties = new java.util.HashMap<>(model.getProperties());
+                mergedProperties.putAll(parent.getProperties());
+                model = model.withProperties(mergedProperties);
             }
 
             // model normalization
@@ -1901,7 +1908,12 @@ protected void mergeModel_Subprojects(
             Model parent = defaultInheritanceAssembler.assembleModelInheritance(raw, parentData, request, this);
             for (Mixin mixin : parent.getMixins()) {
                 Model parentModel = resolveParent(parent, mixin, childProfileActivationContext, parentChain);
+                // Merge mixin into parent
                 parent = defaultInheritanceAssembler.assembleModelInheritance(parent, parentModel, request, this);
+                // Ensure mixin properties override any previously inherited properties
+                Map<String, String> mergedProperties = new java.util.HashMap<>(parent.getProperties());
+                mergedProperties.putAll(parentModel.getProperties());
+                parent = parent.withProperties(mergedProperties);
             }
 
             // Profile injection SHOULD be performed on parent models to ensure

its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng11133MixinsPrecedenceTest.java

@@ -0,0 +1,49 @@
+/*
+ * 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.it;
+
+import java.io.File;
+import java.nio.file.Files;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * MNG-11133: Mixins should override properties inherited from parent.
+ */
+public class MavenITmng11133MixinsPrecedenceTest extends AbstractMavenIntegrationTestCase {
+
+    @Test
+    public void testMixinOverridesParentProperty() throws Exception {
+        File testDir = extractResources("/mng-11133-mixins/project");
+
+        Verifier verifier = newVerifier(testDir.getAbsolutePath());
+        verifier.setAutoclean(false);
+        verifier.deleteDirectory("target");
+        verifier.addCliArgument("help:effective-pom");
+        verifier.addCliArgument("-Doutput=target/effective-pom.xml");
+        verifier.execute();
+        verifier.verifyErrorFreeLog();
+
+        verifier.verifyFilePresent("target/effective-pom.xml");
+        String effectivePom = Files.readString(new File(testDir, "target/effective-pom.xml").toPath());
+        assertTrue(effectivePom.contains("<maven.compiler.release>21</maven.compiler.release>"));
+    }
+}

its/core-it-suite/src/test/resources/mng-11133-mixins/mixins/mixin.xml

@@ -0,0 +1,32 @@
+<?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 xmlns="http://maven.apache.org/POM/4.2.0">
+  <modelVersion>4.2.0</modelVersion>
+
+  <groupId>org.apache.maven.its.mng11133</groupId>
+  <artifactId>mixin-jdk-21</artifactId>
+  <version>1.0.0</version>
+  <packaging>pom</packaging>
+
+  <properties>
+    <maven.compiler.release>21</maven.compiler.release>
+  </properties>
+</project>
+

its/core-it-suite/src/test/resources/mng-11133-mixins/parent/pom.xml

@@ -0,0 +1,31 @@
+<?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 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>
+
+  <groupId>org.apache.maven.its.mng11133</groupId>
+  <artifactId>parent</artifactId>
+  <version>1.0</version>
+  <packaging>pom</packaging>
+
+  <properties>
+    <maven.compiler.release>11</maven.compiler.release>
+  </properties>
+</project>

its/core-it-suite/src/test/resources/mng-11133-mixins/project/pom.xml

@@ -0,0 +1,39 @@
+<?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 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>
+
+  <parent>
+    <groupId>org.apache.maven.its.mng11133</groupId>
+    <artifactId>parent</artifactId>
+    <version>1.0</version>
+    <relativePath>../parent/pom.xml</relativePath>
+  </parent>
+
+  <groupId>org.apache.maven.its.mng11133</groupId>
+  <artifactId>project</artifactId>
+  <version>1.0</version>
+
+  <mixins>
+    <mixin>
+      <relativePath>../mixins/mixin.xml</relativePath>
+    </mixin>
+  </mixins>
+</project>