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

src/main/java/org/apache/maven/plugins/install/InstallMojo.java

@@ -29,6 +29,7 @@
 import org.apache.maven.api.ProducedArtifact;
 import org.apache.maven.api.Project;
 import org.apache.maven.api.Session;
+import org.apache.maven.api.SourceRoot;
 import org.apache.maven.api.di.Inject;
 import org.apache.maven.api.model.Plugin;
 import org.apache.maven.api.plugin.Log;
@@ -249,6 +250,7 @@ private ArtifactInstallerRequest processProject(Project project) {
         ProjectManager projectManager = getProjectManager();
         Collection<ProducedArtifact> installables = projectManager.getAllArtifacts(project);
         Collection<ProducedArtifact> attachedArtifacts = projectManager.getAttachedArtifacts(project);
+        List<ProducedArtifact> toInstall = new ArrayList<>(installables);
 
         getArtifactManager().setPath(project.getPomArtifact(), project.getPomPath());
 
@@ -258,19 +260,19 @@ private ArtifactInstallerRequest processProject(Project project) {
                     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;"
+                                + " installing POM and per-module artifacts only.");
+                        toInstall.remove(installable);
+                    } 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!");
+                        toInstall.remove(installable);
                     } 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 "
@@ -279,13 +281,19 @@ private ArtifactInstallerRequest processProject(Project project) {
             }
         }
 
-        return ArtifactInstallerRequest.build(session, installables);
+        return ArtifactInstallerRequest.build(session, toInstall);
     }
 
     private boolean isValidPath(Artifact a) {
         return getArtifactManager().getPath(a).filter(Files::isRegularFile).isPresent();
     }
 
+    private static boolean usesModuleSourceHierarchy(Project project, ProjectManager projectManager) {
+        return projectManager.getSourceRoots(project).stream()
+                .filter(SourceRoot::enabled)
+                .anyMatch(sr -> sr.module().isPresent());
+    }
+
     void setSkip(boolean skip) {
         this.skip = skip;
     }

src/test/java/org/apache/maven/plugins/install/InstallMojoTest.java

@@ -27,12 +27,14 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.atomic.AtomicReference;
 
 import org.apache.maven.api.Artifact;
 import org.apache.maven.api.MojoExecution;
 import org.apache.maven.api.ProducedArtifact;
 import org.apache.maven.api.Project;
+import org.apache.maven.api.SourceRoot;
 import org.apache.maven.api.di.Inject;
 import org.apache.maven.api.di.Named;
 import org.apache.maven.api.di.Priority;
@@ -154,6 +156,35 @@ void basicInstallWithAttachedArtifacts(InstallMojo mojo) throws Exception {
                 artifacts.stream().map(Artifact::key).toList());
     }
 
+    @Test
+    @InjectMojo(goal = "install")
+    @MojoParameter(name = "installAtEnd", value = "false")
+    void moduleSourceHierarchySkipsMainArtifact(InstallMojo mojo) throws Exception {
+        assertNotNull(mojo);
+        Project project = (Project) getVariableValueFromObject(mojo, "project");
+
+        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));
+
+        projectManager.attachArtifact(
+                project,
+                new ProducedArtifactStub("org.apache.maven.test", "org.example.module", "", "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"));
+
+        ArtifactInstallerRequest request = execute(mojo);
+
+        assertNotNull(request);
+        Collection<ProducedArtifact> artifacts = request.getArtifacts();
+        assertEquals(
+                Arrays.asList(
+                        "org.apache.maven.test:maven-install-test:pom:1.0-SNAPSHOT",
+                        "org.apache.maven.test:org.example.module:jar:1.0-SNAPSHOT"),
+                artifacts.stream().map(Artifact::key).toList());
+    }
+
     @Test
     @InjectMojo(goal = "install")
     void installIfArtifactFileIsNull(InstallMojo mojo) throws Exception {