IJPL-232406 Remove ProjectExtension

GitOrigin-RevId: 4940b5614a90b18fd37eafdf3df68edcbe96b4c3

java/java-impl/src/com/intellij/openapi/roots/impl/LanguageLevelProjectExtensionImpl.java

@@ -9,9 +9,12 @@ import com.intellij.openapi.projectRoots.JavaSdk;
 import com.intellij.openapi.projectRoots.JavaSdkVersion;
 import com.intellij.openapi.projectRoots.Sdk;
 import com.intellij.openapi.roots.LanguageLevelProjectExtension;
-import com.intellij.openapi.roots.ProjectExtension;
 import com.intellij.openapi.roots.ProjectRootManager;
 import com.intellij.platform.backend.workspace.WorkspaceModel;
+import com.intellij.platform.backend.workspace.WorkspaceModelChangeListener;
+import com.intellij.platform.backend.workspace.WorkspaceModelTopics;
+import com.intellij.platform.workspace.jps.entities.ProjectSettingsEntity;
+import com.intellij.platform.workspace.storage.VersionedStorageChange;
 import com.intellij.pom.java.JavaRelease;
 import com.intellij.pom.java.LanguageLevel;
 import com.intellij.util.ObjectUtils;
@@ -39,6 +42,15 @@ public final class LanguageLevelProjectExtensionImpl extends LanguageLevelProjec
 
   public LanguageLevelProjectExtensionImpl(final Project project) {
     myProject = project;
+
+    myProject.getMessageBus().simpleConnect().subscribe(WorkspaceModelTopics.CHANGED, new WorkspaceModelChangeListener() {
+      @Override
+      public void changed(@NotNull VersionedStorageChange event) {
+        if (!event.getChanges(ProjectSettingsEntity.class).isEmpty()) {
+          projectSdkChanged(ProjectRootManager.getInstance(myProject).getProjectSdk());
+        }
+      }
+    });
   }
 
   public static LanguageLevelProjectExtensionImpl getInstanceImpl(Project project) {
@@ -166,16 +178,4 @@ public final class LanguageLevelProjectExtensionImpl extends LanguageLevelProjec
     setLanguageLevelInternal(null, null);
   }
 
-  static final class MyProjectExtension extends ProjectExtension {
-    private final LanguageLevelProjectExtensionImpl myInstance;
-
-    MyProjectExtension(@NotNull Project project) {
-      myInstance = ((LanguageLevelProjectExtensionImpl)getInstance(project));
-    }
-
-    @Override
-    public void projectSdkChanged(@Nullable Sdk sdk) {
-      myInstance.projectSdkChanged(sdk);
-    }
-  }
 }

java/java-tests/testSrc/com/intellij/openapi/roots/impl/LanguageLevelProjectExtensionTest.java

@@ -0,0 +1,45 @@
+// Copyright 2000-2026 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package com.intellij.openapi.roots.impl;
+
+import com.intellij.openapi.application.WriteAction;
+import com.intellij.openapi.projectRoots.ProjectJdkTable;
+import com.intellij.openapi.projectRoots.Sdk;
+import com.intellij.openapi.roots.LanguageLevelProjectExtension;
+import com.intellij.openapi.roots.ProjectRootManager;
+import com.intellij.pom.java.LanguageLevel;
+import com.intellij.testFramework.IdeaTestUtil;
+import com.intellij.testFramework.JavaProjectTestCase;
+
+public class LanguageLevelProjectExtensionTest extends JavaProjectTestCase {
+
+  public void testLanguageLevelChangesWhenProjectSdkChanges() {
+    LanguageLevelProjectExtension extension = LanguageLevelProjectExtension.getInstance(myProject);
+
+    Sdk jdk17 = IdeaTestUtil.getMockJdk17();
+    WriteAction.run(() -> ProjectJdkTable.getInstance().addJdk(jdk17, getTestRootDisposable()));
+
+    // Initialize: set language level to JDK 17 with default=true
+    // This enables automatic language level updates when SDK changes
+    WriteAction.run(() -> {
+      extension.setLanguageLevel(LanguageLevel.JDK_1_7);
+      extension.setDefault(true);
+    });
+
+    WriteAction.run(() -> ProjectRootManager.getInstance(myProject).setProjectSdk(jdk17));
+
+    assertTrue("Language level should be default", extension.isDefault());
+    assertEquals("Language level should match JDK 1.7",
+                 LanguageLevel.JDK_1_7, extension.getLanguageLevel());
+
+    Sdk jdk18 = IdeaTestUtil.getMockJdk18();
+    WriteAction.run(() -> ProjectJdkTable.getInstance().addJdk(jdk18, getTestRootDisposable()));
+
+    // Change project SDK to JDK 1.8 - this should trigger language level update
+    WriteAction.run(() -> ProjectRootManager.getInstance(myProject).setProjectSdk(jdk18));
+
+    // Verify language level changed to JDK_1_8
+    assertTrue("Language level should still be default", extension.isDefault());
+    assertEquals("Language level should match JDK 1.8",
+                 LanguageLevel.JDK_1_8, extension.getLanguageLevel());
+  }
+}

platform/external-system-impl/src/com/intellij/openapi/externalSystem/service/RemoteExternalSystemCommunicationManager.java

@@ -36,7 +36,6 @@ import com.intellij.openapi.project.Project;
 import com.intellij.openapi.projectRoots.SdkType;
 import com.intellij.openapi.projectRoots.SimpleJavaSdkType;
 import com.intellij.openapi.roots.DependencyScope;
-import com.intellij.openapi.roots.ProjectExtension;
 import com.intellij.openapi.util.ShutDownTracker;
 import com.intellij.serialization.ObjectSerializer;
 import com.intellij.ui.PlaceHolder;
@@ -116,7 +115,6 @@ public final class RemoteExternalSystemCommunicationManager implements ExternalS
         ContainerUtil.addIfNotNull(classPath, getJarPathForClass(Project.class)); //intellij.platform.core
         ContainerUtil.addIfNotNull(classPath, getJarPathForClass(PlaceHolder.class)); //intellij.platform.editor
         ContainerUtil.addIfNotNull(classPath, getJarPathForClass(DependencyScope.class)); //intellij.platform.projectModel
-        ContainerUtil.addIfNotNull(classPath, getJarPathForClass(ProjectExtension.class)); //intellij.platform.projectModel.impl
         ContainerUtil.addIfNotNull(classPath, getJarPathForClass(Alarm.class)); //intellij.platform.ide
         ContainerUtil.addIfNotNull(classPath, getJarPathForClass(ExtensionPointName.class)); //intellij.platform.extensions
         ContainerUtil.addIfNotNull(classPath, getJarPathForClass(StorageUtilKt.class)); //intellij.platform.ide.impl

platform/projectModel-impl/resources/META-INF/ProjectModelImpl.xml

@@ -2,7 +2,6 @@
   <extensionPoints>
     <extensionPoint name="additionalLibraryRootsProvider" interface="com.intellij.openapi.roots.AdditionalLibraryRootsProvider"
                     dynamic="true"/>
-    <extensionPoint name="projectExtension" interface="com.intellij.openapi.roots.ProjectExtension" area="IDEA_PROJECT" dynamic="true"/>
     <extensionPoint name="workspaceModel.moduleExtensionBridgeFactory"
                     interface="com.intellij.workspaceModel.ide.legacyBridge.ModuleExtensionBridgeFactory"
                     dynamic="true"/>

platform/projectModel-impl/src/com/intellij/openapi/roots/ProjectExtension.java

@@ -1,21 +0,0 @@
-// Copyright 2000-2023 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
-package com.intellij.openapi.roots;
-
-import com.intellij.openapi.projectRoots.Sdk;
-import org.jdom.Element;
-import org.jetbrains.annotations.ApiStatus;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
-
-/**
- * Provides a way to store additional configuration for a project. Plugins must not use this class, but use project-level
- * <a href="https://plugins.jetbrains.com/docs/intellij/plugin-services.html">services</a> implementing {@link com.intellij.openapi.components.PersistentStateComponent}
- * instead.
- *
- * <p>This class is used for some data which is historically stored as part of {@code ProjectRootManager} configuration in .idea/misc.xml file.</p>
- */
-@ApiStatus.Internal
-public abstract class ProjectExtension {
-  public void projectSdkChanged(@Nullable Sdk sdk) {
-  }
-}

platform/projectModel-impl/src/com/intellij/openapi/roots/impl/ProjectRootManagerImpl.kt

@@ -1,10 +1,9 @@
-// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+// Copyright 2000-2026 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.openapi.roots.impl
 
 import com.intellij.openapi.application.ApplicationManager
 import com.intellij.openapi.components.State
 import com.intellij.openapi.diagnostic.logger
-import com.intellij.openapi.extensions.ProjectExtensionPointName
 import com.intellij.openapi.module.Module
 import com.intellij.openapi.module.ModuleManager
 import com.intellij.openapi.project.ModuleListener
@@ -36,8 +35,6 @@ import java.util.concurrent.ConcurrentHashMap
 
 private val LOG = logger<ProjectRootManagerImpl>()
 
-private val EP_NAME = ProjectExtensionPointName<ProjectExtension>("com.intellij.projectExtension")
-
 @State(name = "ProjectRootManager")
 @ApiStatus.Internal
 open class ProjectRootManagerImpl(
@@ -314,14 +311,6 @@ open class ProjectRootManagerImpl(
     // There is no mergeRootsChangesDuring because currently it has a bug: "after" event will never fire if mergeRootsChangesDuring
     // is invoked while another rootsChange event (caused by the WSM change) is in progress (see RootsChangedTest).
     actionToRunWhenProjectJdkChanges.run()
-    fireJdkChanged()
-  }
-
-  private fun fireJdkChanged() {
-    val sdk = getProjectSdk()
-    for (extension in EP_NAME.getExtensions(project)) {
-      extension.projectSdkChanged(sdk)
-    }
   }
 
   @get:ApiStatus.Internal