Fix site lifecycle reactor dependency resolution

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

@@ -40,6 +40,7 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.jar.JarOutputStream;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -217,13 +218,43 @@ private File determineBuildOutputDirectoryForArtifact(final MavenProject project
             if (projectHasOutputFromPreviousSession || projectCompiledDuringThisSession) {
                 return outputDirectory;
             }
+
+            if (hasSiteLifecyclePhase(project) && "jar".equals(artifact.getExtension()) && "jar".equals(type)) {
+                return ensureEmptyArtifactFile(artifact);
+            }
         }
 
         // The fall-through indicates that the artifact cannot be found;
         // for instance if package produced nothing or classifier problems.
         return null;
     }
 
+    private File ensureEmptyArtifactFile(final Artifact artifact) {
+        Path target = getArtifactPath(artifact);
+        synchronized (this) {
+            if (Files.isRegularFile(target)) {
+                return target.toFile();
+            }
+            try {
+                Files.createDirectories(target.getParent());
+                try (JarOutputStream ignored = new JarOutputStream(Files.newOutputStream(target))) {
+                    // create an empty jar for site reports that inspect reactor artifacts before package
+                }
+                return target.toFile();
+            } catch (IOException e) {
+                LOGGER.warn("Unable to create empty reactor artifact for '{}'.", artifact, e);
+                return null;
+            }
+        }
+    }
+
+    private boolean hasSiteLifecyclePhase(MavenProject project) {
+        return project.hasLifecyclePhase("pre-site")
+                || project.hasLifecyclePhase("site")
+                || project.hasLifecyclePhase("post-site")
+                || project.hasLifecyclePhase("site-deploy");
+    }
+
     private boolean isPackagedArtifactUpToDate(MavenProject project, File packagedArtifactFile) {
         Path outputDirectory = Paths.get(project.getBuild().getOutputDirectory());
         if (!outputDirectory.toFile().exists()) {

its/core-it-suite/src/test/java/org/apache/maven/it/MavenITgh12064SiteReactorDependenciesTest.java

@@ -0,0 +1,48 @@
+/*
+ * 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;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+/**
+ * This is a test set for <a href="https://github.com/apache/maven/issues/12064">GH-12064</a>.
+ */
+class MavenITgh12064SiteReactorDependenciesTest extends AbstractMavenIntegrationTestCase {
+
+    @Test
+    void testSiteLifecycleResolvesReactorDependencies() throws Exception {
+        File testDir = extractResources("/gh-12064-site-reactor-dependencies");
+
+        Verifier verifier = newVerifier(testDir.getAbsolutePath());
+        verifier.setAutoclean(false);
+        verifier.deleteDirectory("producer/target");
+        verifier.deleteDirectory("consumer/target");
+        verifier.deleteArtifacts("org.apache.maven.its.gh12064");
+        verifier.addCliArgument("site");
+        verifier.execute();
+        verifier.verifyErrorFreeLog();
+
+        verifier.verifyFilePresent("consumer/target/site/dependencies.html");
+        assertFalse(new File(testDir, "producer/target/classes").exists(), "site must not require compile first");
+    }
+}

its/core-it-suite/src/test/resources/gh-12064-site-reactor-dependencies/consumer/pom.xml

@@ -0,0 +1,40 @@
+<?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/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.apache.maven.its.gh12064</groupId>
+    <artifactId>parent</artifactId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>consumer</artifactId>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.apache.maven.its.gh12064</groupId>
+      <artifactId>producer</artifactId>
+      <version>1.0-SNAPSHOT</version>
+    </dependency>
+  </dependencies>
+</project>

its/core-it-suite/src/test/resources/gh-12064-site-reactor-dependencies/consumer/src/main/java/org/apache/maven/its/gh12064/Consumer.java

@@ -0,0 +1,25 @@
+/*
+ * 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.its.gh12064;
+
+public class Consumer {
+    public String message() {
+        return Producer.message();
+    }
+}

its/core-it-suite/src/test/resources/gh-12064-site-reactor-dependencies/pom.xml

@@ -0,0 +1,38 @@
+<?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/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>org.apache.maven.its.gh12064</groupId>
+  <artifactId>parent</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <packaging>pom</packaging>
+
+  <modules>
+    <module>producer</module>
+    <module>consumer</module>
+  </modules>
+
+  <properties>
+    <maven.compiler.release>17</maven.compiler.release>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+</project>

its/core-it-suite/src/test/resources/gh-12064-site-reactor-dependencies/producer/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/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.apache.maven.its.gh12064</groupId>
+    <artifactId>parent</artifactId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>producer</artifactId>
+</project>

its/core-it-suite/src/test/resources/gh-12064-site-reactor-dependencies/producer/src/main/java/org/apache/maven/its/gh12064/Producer.java

@@ -0,0 +1,25 @@
+/*
+ * 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.its.gh12064;
+
+public class Producer {
+    public static String message() {
+        return "producer";
+    }
+}