disable "theOnlyProject" optimization when the default project is alive to avoid confusion when "Settings|Code style" code fragments expect their .getProject() to return DefaultProject

platform/core-api/src/com/intellij/openapi/project/ProjectCoreUtil.java

@@ -20,10 +20,14 @@ import com.intellij.openapi.fileTypes.FileTypeRegistry;
 import com.intellij.openapi.fileTypes.InternalFileType;
 import com.intellij.openapi.vfs.VfsUtilCore;
 import com.intellij.openapi.vfs.VirtualFile;
+import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+
 public class ProjectCoreUtil {
+  @Deprecated
+  @ApiStatus.Experimental
   public static volatile Project theProject;
 
   public static boolean isProjectOrWorkspaceFile(@NotNull VirtualFile file) {
@@ -37,7 +41,7 @@ public class ProjectCoreUtil {
   }
 
   /**
-   * @return the only open project if there is one, null if no or several projects are open
+   * @return the only open project if there is one, null if no projects open, or several projects are open, or default project is created
    */
   @Nullable
   public static Project theOnlyOpenProject() {

platform/platform-impl/src/com/intellij/openapi/project/impl/DefaultProject.java

@@ -2,6 +2,8 @@
 package com.intellij.openapi.project.impl;
 
 import com.intellij.openapi.components.ComponentConfig;
+import com.intellij.openapi.diagnostic.Logger;
+import com.intellij.openapi.project.ProjectManager;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -9,10 +11,14 @@ import org.jetbrains.annotations.Nullable;
  * @author peter
  */
 final class DefaultProject extends ProjectImpl {
+  private static final Logger LOG = Logger.getInstance(DefaultProject.class);
   private static final String TEMPLATE_PROJECT_NAME = "Default (Template) Project";
 
   DefaultProject(@NotNull String filePath) {
     super(filePath, TEMPLATE_PROJECT_NAME);
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("Created DefaultProject " + this, new Exception());
+    }
   }
 
   @Override
@@ -38,4 +44,13 @@ final class DefaultProject extends ProjectImpl {
   protected boolean isComponentSuitable(@NotNull ComponentConfig componentConfig) {
     return super.isComponentSuitable(componentConfig) && componentConfig.isLoadForDefaultProject();
   }
+
+  @Override
+  public synchronized void dispose() {
+    super.dispose();
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("Disposed DefaultProject "+this);
+    }
+    ((ProjectManagerImpl)ProjectManager.getInstance()).updateTheOnlyProjectField();
+  }
 }

platform/platform-impl/src/com/intellij/openapi/project/impl/ProjectManagerImpl.java

@@ -336,7 +336,11 @@ public class ProjectManagerImpl extends ProjectManagerEx implements Disposable {
   @NotNull
   public synchronized Project getDefaultProject() {
     LOG.assertTrue(!ApplicationManager.getApplication().isDisposed(), "Default project has been already disposed!");
-    return myDefaultProjectTimed.get();
+    Project defaultProject = myDefaultProjectTimed.get();
+    // disable "the only project" optimization since we have now more than one project.
+    // (even though the default project is not a real project, it can be used indirectly in e.g. "Settings|Code Style" code fragments PSI)
+    updateTheOnlyProjectField();
+    return defaultProject;
   }
 
   @Override
@@ -440,18 +444,22 @@ public class ProjectManagerImpl extends ProjectManagerEx implements Disposable {
         return false;
       }
       myOpenProjects = ArrayUtil.append(myOpenProjects, project);
-      //noinspection AssignmentToStaticFieldFromInstanceMethod
-      ProjectCoreUtil.theProject = myOpenProjects.length == 1 ? project : null;
+      updateTheOnlyProjectField();
       myOpenProjectByHash.put(project.getLocationHash(), project);
     }
     return true;
   }
 
+  void updateTheOnlyProjectField() {
+    synchronized (lock) {
+      ProjectCoreUtil.theProject = myOpenProjects.length == 1 && !isDefaultProjectInitialized() ? myOpenProjects[0] : null;
+    }
+  }
+
   private void removeFromOpened(@NotNull Project project) {
     synchronized (lock) {
       myOpenProjects = ArrayUtil.remove(myOpenProjects, project);
-      //noinspection AssignmentToStaticFieldFromInstanceMethod
-      ProjectCoreUtil.theProject = myOpenProjects.length == 1 ? myOpenProjects[0] : null;
+      updateTheOnlyProjectField();
       myOpenProjectByHash.values().remove(project); // remove by value and not by key!
     }
   }