Auto-detect module source hierarchy and skip main artifact at deploy

src/main/java/org/apache/maven/plugins/deploy/DeployMojo.java

@@ -33,6 +33,7 @@
 import org.apache.maven.api.ProducedArtifact;
 import org.apache.maven.api.Project;
 import org.apache.maven.api.RemoteRepository;
+import org.apache.maven.api.SourceRoot;
 import org.apache.maven.api.di.Inject;
 import org.apache.maven.api.model.DistributionManagement;
 import org.apache.maven.api.model.Plugin;
@@ -436,6 +437,7 @@ private ArtifactDeployerRequest createDeployerRequest() {
                     + ":" + project.getVersion() + " are not valid: they use invalid characters.");
         }
 
+        List<ProducedArtifact> toDeploy = new ArrayList<>(deployables);
         for (Artifact deployable : deployables) {
             if (!isValidClassifier(deployable.getClassifier())) {
                 throw new MojoException("The classifier of attached artifact " + deployable
@@ -446,19 +448,19 @@ private ArtifactDeployerRequest createDeployerRequest() {
                     if (attachedArtifacts.isEmpty()) {
                         throw new MojoException(
                                 "The packaging for this project did not assign a file to the build artifact");
+                    } else if (usesModuleSourceHierarchy(project, projectManager)) {
+                        getLog().info("Module source hierarchy: no main artifact produced;"
+                                + " deploying POM and per-module artifacts only.");
+                        toDeploy.remove(deployable);
+                    } else if (allowIncompleteProjects) {
+                        getLog().warn("The packaging plugin for this project did not assign"
+                                + " a main file to the project but it has attachments."
+                                + " Change packaging to 'pom'."
+                                + " Incomplete projects like this will fail in future Maven versions!");
+                        toDeploy.remove(deployable);
                     } else {
-                        if (allowIncompleteProjects) {
-                            getLog().warn("");
-                            getLog().warn("The packaging plugin for this project did not assign");
-                            getLog().warn(
-                                            "a main file to the project but it has attachments. Change packaging to 'pom'.");
-                            getLog().warn("");
-                            getLog().warn("Incomplete projects like this will fail in future Maven versions!");
-                            getLog().warn("");
-                        } else {
-                            throw new MojoException("The packaging plugin for this project did not assign "
-                                    + "a main file to the project but it has attachments. Change packaging to 'pom'.");
-                        }
+                        throw new MojoException("The packaging plugin for this project did not assign "
+                                + "a main file to the project but it has attachments. Change packaging to 'pom'.");
                     }
                 } else {
                     throw new MojoException("The packaging for this project did not assign "
@@ -470,7 +472,7 @@ private ArtifactDeployerRequest createDeployerRequest() {
         ArtifactDeployerRequest request = ArtifactDeployerRequest.builder()
                 .session(session)
                 .repository(getDeploymentRepository(session.isVersionSnapshot(project.getVersion())))
-                .artifacts(deployables)
+                .artifacts(toDeploy)
                 .retryFailedDeploymentCount(Math.max(1, Math.min(10, getRetryFailedDeploymentCount())))
                 .build();
 
@@ -681,6 +683,12 @@ private void warnIfPolicyMismatch(org.apache.maven.api.model.DeploymentRepositor
         }
     }
 
+    private static boolean usesModuleSourceHierarchy(Project project, ProjectManager projectManager) {
+        return projectManager.getSourceRoots(project).stream()
+                .filter(SourceRoot::enabled)
+                .anyMatch(sr -> sr.module().isPresent());
+    }
+
     private boolean isValidPath(Artifact a) {
         return getArtifactManager().getPath(a).filter(Files::isRegularFile).isPresent();
     }

src/test/java/org/apache/maven/plugins/deploy/DeployMojoTest.java

@@ -25,12 +25,14 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.stream.Collectors;
 
 import org.apache.maven.api.Artifact;
 import org.apache.maven.api.ProducedArtifact;
 import org.apache.maven.api.Project;
 import org.apache.maven.api.RemoteRepository;
+import org.apache.maven.api.SourceRoot;
 import org.apache.maven.api.di.Inject;
 import org.apache.maven.api.di.Priority;
 import org.apache.maven.api.di.Provides;
@@ -68,6 +70,7 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
 /**
@@ -569,6 +572,45 @@ void ambiguousLegacyAltDeploymentRepositoryRefused(DeployMojo mojo) throws Excep
         assertEquals("Ambiguous syntax for alternative repository.", e.getMessage());
     }
 
+    @Test
+    @InjectMojo(goal = "deploy")
+    @MojoParameter(name = "deployAtEnd", value = "false")
+    void moduleSourceHierarchySkipsMainArtifactAtDeploy(DeployMojo mojo) throws Exception {
+        assertNotNull(mojo);
+        Project project = (Project) getVariableValueFromObject(mojo, "project");
+
+        // Simulate module source hierarchy: main artifact path is a directory (the build output dir)
+        artifactManager.setPath(project.getMainArtifact().get(), Paths.get(getBasedir(), "target/test-classes"));
+
+        // Attach a per-module JAR as the real deployable artifact
+        ProducedArtifactStub moduleJar = new ProducedArtifactStub(
+                "org.apache.maven.test", "maven-deploy-test", "module.one", "1.0-SNAPSHOT", "jar");
+        projectManager.attachArtifact(
+                project,
+                moduleJar,
+                Paths.get(getBasedir(), "target/test-classes/unit/maven-deploy-test-1.0-SNAPSHOT.jar"));
+
+        // Stub a module source root on the projectManager
+        SourceRoot moduleRoot = mock(SourceRoot.class);
+        when(moduleRoot.enabled()).thenReturn(true);
+        when(moduleRoot.module()).thenReturn(Optional.of("org.example.module"));
+        when(projectManager.getSourceRoots(project)).thenReturn(List.of(moduleRoot));
+
+        ArtifactDeployerRequest request = execute(mojo);
+
+        assertNotNull(request);
+        Collection<ProducedArtifact> artifacts = request.getArtifacts();
+        // Main artifact (directory) must be excluded; POM and per-module JAR must be deployed
+        List<String> keys = artifacts.stream().map(Artifact::key).collect(Collectors.toList());
+        assertFalse(
+                keys.contains("org.apache.maven.test:maven-deploy-test:jar:1.0-SNAPSHOT"),
+                "directory main artifact must be excluded from deploy request");
+        assertTrue(keys.contains("org.apache.maven.test:maven-deploy-test:pom:1.0-SNAPSHOT"), "POM must be deployed");
+        assertTrue(
+                keys.contains("org.apache.maven.test:maven-deploy-test:jar:module.one:1.0-SNAPSHOT"),
+                "per-module JAR must be deployed");
+    }
+
     private ArtifactDeployerRequest execute(DeployMojo mojo) {
         ArgumentCaptor<ArtifactDeployerRequest> requestCaptor = ArgumentCaptor.forClass(ArtifactDeployerRequest.class);
         doNothing().when(artifactDeployer).deploy(requestCaptor.capture());