Fix ReactorReader to prefer consumer POMs over build POMs (apache#11107)

* ReactorReader: prefer consumer POM from project-local repo when resolving POMs

When only part of a reactor is built, ReactorReader mirrors artifacts into a project-local repo. If a module depends on another reactor module not in the current session, POM resolution may hit that repo. Today, the main POM path contains the build POM, which can include Maven-4 build-time constructs and be invalid as a repository POM (e.g., missing parent.*). As a result, dependency resolution can fail with fatal model errors.

Teach ReactorReader to prefer the consumer POM (classifier=consumer) for POM artifacts when present in the project-local repo, falling back to the main POM otherwise. This avoids consuming a build POM from the project-local repo without changing the repo contents or layout.

* Fix ReactorReader to prefer consumer POMs over build POMs

When building modules in isolation (outside of the full reactor), the
ReactorReader should prefer consumer POMs from the project-local repository
over build POMs to avoid invalid POM elements like <parent />.

The findModel method now:
1. First checks if the project is in the current reactor session
2. If not found, looks for a consumer POM in the project-local repository
3. Uses the same consumer POM preference logic as findInProjectLocalRepository

This eliminates 'invalid POM' warnings when building modules in isolation
while maintaining backward compatibility for reactor builds.

Fixes apachegh-11084

* Fix

(cherry picked from commit 93b85b0)

Author: gnodet

impl/maven-core/src/main/java/org/apache/maven/ReactorReader.java

@@ -330,6 +330,18 @@ private static boolean isTestArtifact(Artifact artifact) {
     }
 
     private File findInProjectLocalRepository(Artifact artifact) {
+        // Prefer the consumer POM when resolving POMs from the project-local repository,
+        // to avoid treating a build POM as a repository (consumer) POM.
+        if ("pom".equals(artifact.getExtension())) {
+            String classifier = artifact.getClassifier();
+            if (classifier == null || classifier.isEmpty()) {
+                Path consumer = getArtifactPath(
+                        artifact.getGroupId(), artifact.getArtifactId(), artifact.getBaseVersion(), "consumer", "pom");
+                if (Files.isRegularFile(consumer)) {
+                    return consumer.toFile();
+                }
+            }
+        }
         Path target = getArtifactPath(artifact);
         return Files.isRegularFile(target) ? target.toFile() : null;
     }

its/core-it-suite/src/test/java/org/apache/maven/it/MavenITgh11084ReactorReaderPreferConsumerPomTest.java

@@ -0,0 +1,51 @@
+/*
+ * 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 org.junit.jupiter.api.Test;
+
+/**
+ * This is a test set for GH-11084.
+ */
+class MavenITgh11084ReactorReaderPreferConsumerPomTest extends AbstractMavenIntegrationTestCase {
+    MavenITgh11084ReactorReaderPreferConsumerPomTest() {
+        super("[4.0.0-rc-2,)");
+    }
+
+    @Test
+    void partialReactorShouldResolveUsingConsumerPom() throws Exception {
+        File testDir = extractResources("/gh-11084-reactorreader-prefer-consumer-pom");
+
+        // First build module a to populate project-local-repo with artifacts including consumer POM
+        Verifier v1 = newVerifier(testDir.getAbsolutePath());
+        v1.addCliArguments("clean", "package", "-X");
+        v1.setLogFileName("log-1.txt");
+        v1.execute();
+        v1.verifyErrorFreeLog();
+
+        // Now build only module b; ReactorReader should pick consumer POM from project-local-repo
+        Verifier v2 = newVerifier(testDir.getAbsolutePath());
+        v2.setLogFileName("log-2.txt");
+        v2.addCliArguments("clean", "compile", "-f", "b", "-X");
+        v2.execute();
+        v2.verifyErrorFreeLog();
+    }
+}

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

@@ -103,6 +103,7 @@ public TestSuiteOrdering() {
          * the tests are to finishing. Newer tests are also more likely to fail, so this is
          * a fail fast technique as well.
          */
+        suite.addTestSuite(MavenITgh11084ReactorReaderPreferConsumerPomTest.class);
         suite.addTestSuite(MavenITgh10312TerminallyDeprecatedMethodInGuiceTest.class);
         suite.addTestSuite(MavenITgh10937QuotedPipesInMavenOptsTest.class);
         suite.addTestSuite(MavenITgh2532DuplicateDependencyEffectiveModelTest.class);

its/core-it-suite/src/test/resources/gh-11084-reactorreader-prefer-consumer-pom/a/pom.xml

@@ -0,0 +1,33 @@
+<?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/4.1.0">
+  <parent />
+
+  <artifactId>a</artifactId>
+  <packaging>jar</packaging>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.codehaus.plexus</groupId>
+      <artifactId>plexus-utils</artifactId>
+      <version>4.0.2</version>
+    </dependency>
+  </dependencies>
+</project>

its/core-it-suite/src/test/resources/gh-11084-reactorreader-prefer-consumer-pom/a/src/main/java/a/A.java

@@ -0,0 +1,30 @@
+/*
+ * 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 a;
+
+import java.io.IOException;
+import java.nio.file.Path;
+
+import org.codehaus.plexus.util.io.CachingOutputStream;
+
+public class A {
+    public static CachingOutputStream newCachingOutputStream(Path p) throws IOException {
+        return new CachingOutputStream(p);
+    }
+}

its/core-it-suite/src/test/resources/gh-11084-reactorreader-prefer-consumer-pom/b/pom.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/4.1.0">
+
+  <parent />
+
+  <artifactId>b</artifactId>
+  <packaging>jar</packaging>
+  <dependencies>
+    <dependency>
+      <groupId>org.apache.maven.its.gh11084</groupId>
+      <artifactId>a</artifactId>
+    </dependency>
+  </dependencies>
+</project>

its/core-it-suite/src/test/resources/gh-11084-reactorreader-prefer-consumer-pom/b/src/main/java/b/B.java

@@ -0,0 +1,30 @@
+/*
+ * 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 b;
+
+import java.nio.file.Paths;
+
+import a.A;
+import org.codehaus.plexus.util.io.CachingOutputStream;
+
+public class B {
+    public static void v() throws Exception {
+        try (CachingOutputStream is = A.newCachingOutputStream(Paths.get("."))) {}
+    }
+}

its/core-it-suite/src/test/resources/gh-11084-reactorreader-prefer-consumer-pom/pom.xml

@@ -0,0 +1,30 @@
+<?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/4.1.0" root="true">
+  <groupId>org.apache.maven.its.gh11084</groupId>
+  <artifactId>reactor-root</artifactId>
+  <version>1.0.0-SNAPSHOT</version>
+  <packaging>pom</packaging>
+
+  <modules>
+    <module>a</module>
+    <module>b</module>
+  </modules>
+</project>