Skip the main artifact when its file is a directory (module source hierarchy)

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

@@ -423,6 +423,7 @@ private ArtifactDeployerRequest createDeployerRequest() {
         ProjectManager projectManager = getProjectManager();
         Collection<ProducedArtifact> deployables = projectManager.getAllArtifacts(project);
         Collection<ProducedArtifact> attachedArtifacts = projectManager.getAttachedArtifacts(project);
+        List<ProducedArtifact> toDeploy = new ArrayList<>(deployables);
 
         ArtifactManager artifactManager = getArtifactManager();
         if (artifactManager.getPath(project.getPomArtifact()).isEmpty()) {
@@ -448,13 +449,14 @@ private ArtifactDeployerRequest createDeployerRequest() {
                                 "The packaging for this project did not assign a file to the build artifact");
                     } 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("");
+                            // The main artifact has no file: its path is e.g. the output directory of a module
+                            // source hierarchy, where the JAR plugin attaches one JAR per Java module instead of
+                            // assigning a single main JAR. Deploy the POM and the attachments only; do not hand
+                            // the directory to the deployer, which would otherwise fail with "is a folder".
+                            getLog().info("The project's main artifact has no file"
+                                    + " (e.g. a module source hierarchy produces one artifact per Java module);"
+                                    + " deploying the POM and the attached artifacts only.");
+                            toDeploy.remove(deployable);
                         } 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'.");
@@ -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();
 

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

@@ -185,6 +185,33 @@ void deployWithAttachedArtifacts(DeployMojo mojo) throws Exception {
                 request.getRepository().getUrl());
     }
 
+    @Test
+    @InjectMojo(goal = "deploy")
+    @MojoParameter(name = "deployAtEnd", value = "false")
+    @MojoParameter(name = "allowIncompleteProjects", value = "true")
+    void mainArtifactWithDirectoryPathIsSkippedWhenAttachmentsExist(DeployMojo mojo) throws Exception {
+        // Module source hierarchy: the JAR plugin attaches one JAR per Java module and never assigns a
+        // file to the main artifact, whose path stays the (directory) build output. Deploy must deploy the
+        // POM + attachments and must NOT hand the directory to the deployer (which fails with "is a folder").
+        assertNotNull(mojo);
+        Project project = (Project) getVariableValueFromObject(mojo, "project");
+        projectManager.attachArtifact(
+                project,
+                new ProducedArtifactStub("org.apache.maven.test", "foo.bar", "", "1.0-SNAPSHOT", "jar"),
+                Paths.get(getBasedir(), "target/test-classes/unit/attached-artifact-test-1.0-SNAPSHOT.jar"));
+        artifactManager.setPath(project.getMainArtifact().get(), Paths.get(getBasedir(), "target/test-classes/unit"));
+
+        ArtifactDeployerRequest request = execute(mojo);
+
+        assertNotNull(request);
+        Collection<ProducedArtifact> artifacts = request.getArtifacts();
+        assertEquals(
+                Arrays.asList(
+                        "org.apache.maven.test:maven-deploy-test:pom:1.0-SNAPSHOT",
+                        "org.apache.maven.test:foo.bar:jar:1.0-SNAPSHOT"),
+                artifacts.stream().map(Artifact::key).collect(Collectors.toList()));
+    }
+
     @Test
     @InjectMojo(goal = "deploy")
     void legacyAltDeploymentRepositoryWithDefaultLayout(DeployMojo mojo) throws Exception {