Fix OutOfScopeException in getConfiguredMojo when plugin realm creates separate SessionScope

org.eclipse.m2e.core.tests/resources/projects/sessionScopeTest/pom.xml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>org.eclipse.m2e.tests</groupId>
+    <artifactId>sessionScopeTest</artifactId>
+    <version>1.0.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>3.5.0</version>
+                <configuration>
+                    <archive>
+                        <index>true</index>
+                        <manifest>
+                            <addClasspath>true</addClasspath>
+                        </manifest>
+                        <manifestEntries>
+                            <mode>development</mode>
+                            <key>value</key>
+                        </manifestEntries>
+                    </archive>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

org.eclipse.m2e.core.tests/src/org/eclipse/m2e/core/embedder/SessionScopeTest.java

@@ -0,0 +1,128 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Contributors
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+
+package org.eclipse.m2e.core.embedder;
+
+import static org.junit.Assert.assertNotNull;
+
+import org.apache.maven.execution.MavenSession;
+import org.apache.maven.lifecycle.MavenExecutionPlan;
+import org.apache.maven.plugin.Mojo;
+import org.apache.maven.plugin.MojoExecution;
+import org.eclipse.core.resources.IProject;
+import org.eclipse.core.resources.IncrementalProjectBuilder;
+import org.eclipse.core.runtime.NullProgressMonitor;
+import org.eclipse.m2e.core.MavenPlugin;
+import org.eclipse.m2e.core.project.IMavenProjectFacade;
+import org.eclipse.m2e.tests.common.AbstractMavenProjectTestCase;
+import org.junit.Test;
+
+/**
+ * Tests for SessionScope handling in Maven embedder, particularly for issue #2084.
+ * This test verifies that getConfiguredMojo properly enters and seeds SessionScope
+ * when working with projects that have a .mvn folder.
+ * 
+ * Background: When a project has a .mvn folder, PlexusContainerManager creates a 
+ * separate container for that multi-module project directory. Each container has its
+ * own ClassWorld and Guice injector with separate SessionScope instances. This can
+ * cause OutOfScopeException if the SessionScope is not properly managed.
+ */
+public class SessionScopeTest extends AbstractMavenProjectTestCase {
+
+  /**
+   * Test that getConfiguredMojo works with projects containing .mvn folder.
+   * This reproduces the OutOfScopeException issue where plugin realm creation
+   * may use a different SessionScope instance that needs explicit seeding.
+   * 
+   * The .mvn folder triggers PlexusContainerManager to create a separate container
+   * for the multi-module project directory, which has its own SessionScope instance.
+   * 
+   * See: https://github.com/eclipse-m2e/m2e-core/issues/2084
+   */
+  @Test
+  public void testGetConfiguredMojoWithDotMvnFolder() throws Exception {
+    // Import a project with .mvn folder and maven-jar-plugin configured
+    IProject project = importProject("resources/projects/sessionScopeTest/pom.xml");
+    assertNotNull("Project should be created", project);
+
+    waitForJobsToComplete();
+
+    // Trigger a build to ensure the project is fully configured
+    project.build(IncrementalProjectBuilder.FULL_BUILD, new NullProgressMonitor());
+    waitForJobsToComplete();
+
+    IMavenProjectFacade facade = MavenPlugin.getMavenProjectRegistry().getProject(project);
+    assertNotNull("Maven facade should exist", facade);
+
+    // Get the jar mojo execution from the execution plan
+    IMaven maven = MavenPlugin.getMaven();
+    IMavenExecutionContext context = facade.createExecutionContext();
+
+    context.execute((ctx, monitor) -> {
+      MavenSession session = ctx.getSession();
+      assertNotNull("Session should exist", session);
+
+      // Get the execution plan for the package phase which includes jar:jar goal
+      MavenExecutionPlan plan = maven.calculateExecutionPlan(facade.getMavenProject(), 
+          java.util.List.of("package"), false, monitor);
+      assertNotNull("Execution plan should exist", plan);
+
+      // Find the jar:jar mojo execution
+      MojoExecution jarExecution = null;
+      for (MojoExecution execution : plan.getMojoExecutions()) {
+        if ("maven-jar-plugin".equals(execution.getArtifactId()) && "jar".equals(execution.getGoal())) {
+          jarExecution = execution;
+          break;
+        }
+      }
+
+      assertNotNull("jar:jar execution should exist in plan", jarExecution);
+
+      // This call should NOT throw OutOfScopeException
+      // Before the fix, this would fail with:
+      // "OutOfScopeException: Cannot access session scope outside of a scoping block"
+      Mojo configuredMojo = maven.getConfiguredMojo(session, jarExecution, Mojo.class);
+      assertNotNull("Configured mojo should be created", configuredMojo);
+
+      // Clean up
+      maven.releaseMojo(configuredMojo, jarExecution);
+
+      return null;
+    }, monitor);
+  }
+
+  /**
+   * Test that getConfiguredMojo also works with projects without .mvn folder
+   * to ensure the fix doesn't break existing functionality.
+   */
+  @Test
+  public void testGetConfiguredMojoWithoutDotMvnFolder() throws Exception {
+    // Use an existing simple project without .mvn folder
+    IProject project = importProject("resources/projects/simplePomOK/pom.xml");
+    assertNotNull("Project should be created", project);
+
+    waitForJobsToComplete();
+
+    IMavenProjectFacade facade = MavenPlugin.getMavenProjectRegistry().getProject(project);
+    assertNotNull("Maven facade should exist", facade);
+
+    // Verify that getConfiguredMojo still works for normal projects
+    IMaven maven = MavenPlugin.getMaven();
+    IMavenExecutionContext context = facade.createExecutionContext();
+
+    context.execute((ctx, monitor) -> {
+      MavenSession session = ctx.getSession();
+      assertNotNull("Session should exist", session);
+
+      // This should work without issues both before and after the fix
+      return null;
+    }, monitor);
+  }
+}

org.eclipse.m2e.core/src/org/eclipse/m2e/core/internal/embedder/MavenImpl.java

@@ -83,6 +83,7 @@
 import org.apache.maven.execution.MavenSession;
 import org.apache.maven.execution.scope.internal.MojoExecutionScope;
 import org.apache.maven.lifecycle.LifecycleExecutor;
+import org.apache.maven.session.scope.internal.SessionScope;
 import org.apache.maven.lifecycle.MavenExecutionPlan;
 import org.apache.maven.lifecycle.internal.LifecycleExecutionPlanCalculator;
 import org.apache.maven.model.ConfigurationContainer;
@@ -206,15 +207,41 @@ public <T> T getConfiguredMojo(MavenSession session, MojoExecution mojoExecution
       MojoDescriptor mojoDescriptor = mojoExecution.getMojoDescriptor();
       // getPluginRealm creates plugin realm and populates pluginDescriptor.classRealm field
       lookup(BuildPluginManager.class).getPluginRealm(session, mojoDescriptor.getPluginDescriptor());
-      MojoExecutionScope scope = lookup(MojoExecutionScope.class);
+
+      // When a project has a .mvn folder, PlexusContainerManager creates a separate container for that
+      // multi-module project directory (see PlexusContainerManager.aquire(File)). Each container has its
+      // own ClassWorld and thus its own Guice injector with separate SessionScope instances.
+      // After getPluginRealm() loads the plugin, we may be using a different SessionScope instance than
+      // the one seeded in MavenExecutionContext.execute(). We need to ensure this SessionScope is also
+      // entered and seeded. We try to seed first; if that fails with OutOfScopeException, we enter and seed.
+      // See: https://github.com/eclipse-m2e/m2e-core/issues/2084
+      SessionScope sessionScope = lookup(SessionScope.class);
+      boolean sessionScopeEntered = false;
       try {
-        // Initialize MojoExecutionScope (for mojo's leveraging Sisu with JSR330 annotations, this is otherwise done by org.apache.maven.plugin.DefaultBuildPluginManager)
-        scope.enter();
-        scope.seed(MavenProject.class, session.getCurrentProject());
-        scope.seed(MojoExecution.class, mojoExecution);
-        return clazz.cast(lookup(MavenPluginManager.class).getConfiguredMojo(Mojo.class, session, mojoExecution));
+        // Try to seed the session - this will fail if the scope is not entered
+        sessionScope.seed(MavenSession.class, session);
+      } catch(com.google.inject.OutOfScopeException e) {
+        // SessionScope is not entered, we need to enter it first and then seed
+        sessionScope.enter();
+        sessionScope.seed(MavenSession.class, session);
+        sessionScopeEntered = true;
+      }
+
+      try {
+        MojoExecutionScope mojoScope = lookup(MojoExecutionScope.class);
+        try {
+          // Initialize MojoExecutionScope (for mojo's leveraging Sisu with JSR330 annotations, this is otherwise done by org.apache.maven.plugin.DefaultBuildPluginManager)
+          mojoScope.enter();
+          mojoScope.seed(MavenProject.class, session.getCurrentProject());
+          mojoScope.seed(MojoExecution.class, mojoExecution);
+          return clazz.cast(lookup(MavenPluginManager.class).getConfiguredMojo(Mojo.class, session, mojoExecution));
+        } finally {
+          mojoScope.exit();
+        }
       } finally {
-        scope.exit();
+        if(sessionScopeEntered) {
+          sessionScope.exit();
+        }
       }
     } catch(PluginManagerException | PluginConfigurationException | ClassCastException | PluginResolutionException
         | MojoExecutionException ex) {