Fix IllegalStateException in ProjectOpenProcessor (#8633)

Migrate
[FlutterProjectOpenProcessor](cci:2://file:///usr/local/google/home/jwren/src/flutter-intellij/src/io/flutter/project/FlutterProjectOpenProcessor.kt:21:0-89:1)
and
[FlutterStudioProjectOpenProcessor](cci:2://file:///usr/local/google/home/jwren/src/flutter-intellij/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.kt:17:0-61:1)
from the deprecated
[doOpenProject](cci:1://file:///usr/local/google/home/jwren/src/flutter-intellij/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.kt:54:2-60:3)
to
[openProjectAsync](cci:1://file:///usr/local/google/home/jwren/src/flutter-intellij/src/io/flutter/project/FlutterProjectOpenProcessor.kt:38:2-54:3)
to fix compatibility with IntelliJ IDEA 2025.3+.

This change involves:
- Converting
[FlutterProjectOpenProcessor](cci:2://file:///usr/local/google/home/jwren/src/flutter-intellij/src/io/flutter/project/FlutterProjectOpenProcessor.kt:21:0-89:1)
to Kotlin.
- Converting
[FlutterStudioProjectOpenProcessor](cci:2://file:///usr/local/google/home/jwren/src/flutter-intellij/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.kt:17:0-61:1)
to Kotlin.
- Implementing
[openProjectAsync](cci:1://file:///usr/local/google/home/jwren/src/flutter-intellij/src/io/flutter/project/FlutterProjectOpenProcessor.kt:38:2-54:3)
using `writeAction` for project setup.
- Enabling Kotlin compilation for the main source set in
[build.gradle.kts](cci:7://file:///usr/local/google/home/jwren/src/flutter-intellij/build.gradle.kts:0:0-0:0).

Fixes #8629 See
https://plugins.jetbrains.com/docs/intellij/project-open-processor.html

Author: jwren

CHANGELOG.md

@@ -13,6 +13,7 @@
 ### Fixed
 
 - Fixed crash when using 3rd party loggers that don't implement `setLevel`. (#8631)
+- Fixed `IllegalStateException` and "Slow operations are prohibited on EDT" when opening projects by migrating `FlutterProjectOpenProcessor` to Kotlin and using `openProjectAsync`. (#8629)
 
 ## 88.1.0
 

build.gradle.kts

@@ -141,6 +141,12 @@ sourceSets {
         "third_party/vmServiceDrivers"
       )
     )
+    kotlin.srcDirs(
+      listOf(
+        "src",
+        "third_party/vmServiceDrivers"
+      )
+    )
     // Add kotlin.srcDirs if we start using Kotlin in the main plugin.
     resources.srcDirs(
       listOf(

src/io/flutter/editor/FlutterStudioProjectOpenProcessor.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright 2025 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+package io.flutter.editor
+
+import com.intellij.openapi.application.writeAction
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.vfs.VirtualFile
+import com.intellij.projectImport.ProjectOpenProcessor
+import com.intellij.ui.EditorNotifications
+import io.flutter.FlutterUtils
+import io.flutter.project.FlutterProjectOpenProcessor
+import io.flutter.pub.PubRoot
+import io.flutter.utils.FlutterModuleUtils
+
+/**
+ * Originally `FlutterStudioProjectOpenProcessor.java`.
+ *
+ * This processor is specific to Android Studio (or when the Flutter Studio plugin is active).
+ * It extends `FlutterProjectOpenProcessor` to provide specialized handling for Android Studio,
+ * particularly ensuring that the project is correctly re-detected if the opening process causes a reload.
+ *
+ * Converted to Kotlin to support `openProjectAsync`.
+ */
+class FlutterStudioProjectOpenProcessor : FlutterProjectOpenProcessor() {
+  override val name: String
+    get() = "Flutter Studio"
+
+  override fun canOpenProject(file: VirtualFile): Boolean =
+    PubRoot.forDirectory(file)?.declaresFlutter() == true
+
+  /**
+   * Replaces the deprecated `doOpenProject`.
+   *
+   * Performs the same logic as the original Java implementation but using `suspend` and `writeAction`.
+   *
+   * Key differences from the base class:
+   * - Explicitly looks up the project again using `FlutterUtils.findProject` after opening, as the project instance might have changed
+   *   (e.g. if the platform closed and reopened it during import).
+   * - Ensures Dart SDK is enabled and notifications are updated.
+   */
+  override suspend fun openProjectAsync(
+    virtualFile: VirtualFile,
+    projectToClose: Project?,
+    forceOpenInNewFrame: Boolean,
+  ): Project? {
+    val importProvider = getDelegateImportProvider(virtualFile) ?: return null
+    val project = importProvider.openProjectAsync(virtualFile, projectToClose, forceOpenInNewFrame)
+    
+    // A callback may have caused the project to be reloaded. Find the new Project object.
+    val newProject = FlutterUtils.findProject(virtualFile.path)
+    if (newProject == null || newProject.isDisposed) {
+      return newProject
+    }
+
+    for (module in FlutterModuleUtils.getModules(newProject)) {
+      if (FlutterModuleUtils.declaresFlutter(module) && !FlutterModuleUtils.isFlutterModule(module)) {
+        writeAction {
+          FlutterModuleUtils.setFlutterModuleType(module)
+        }
+        FlutterModuleUtils.enableDartSDK(module)
+      }
+    }
+    newProject.save()
+    EditorNotifications.getInstance(newProject).updateAllNotifications()
+    
+    return newProject
+  }
+
+  override fun doOpenProject(
+    virtualFile: VirtualFile,
+    projectToClose: Project?,
+    forceOpenInNewFrame: Boolean,
+  ): Project? {
+    return null
+  }
+}

src/io/flutter/editor/FlutterStudioProjectOpenProcessor.kt

@@ -0,0 +1,114 @@
+/*
+ * Copyright 2025 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+package io.flutter.project
+
+import com.intellij.openapi.application.ApplicationInfo
+import com.intellij.openapi.application.writeAction
+import com.intellij.openapi.module.Module
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.vfs.VirtualFile
+import com.intellij.projectImport.ProjectOpenProcessor
+import icons.FlutterIcons
+import io.flutter.FlutterBundle
+import io.flutter.FlutterUtils
+import io.flutter.pub.PubRoot
+import io.flutter.utils.FlutterModuleUtils
+import java.util.Objects
+import javax.swing.Icon
+
+/**
+ * Originally `FlutterProjectOpenProcessor.java`.
+ *
+ * This processor handles opening Flutter projects when they are selected directly (e.g. via "Open" in the IDE).
+ * It delegates the actual opening to the platform's default processor (e.g. Gradle or Maven processor if applicable,
+ * or the generic project opener) and then ensures that any modules in the project are correctly configured as Flutter modules.
+ *
+ * Converted to Kotlin to support `openProjectAsync` which is a suspend function.
+ */
+open class FlutterProjectOpenProcessor : ProjectOpenProcessor() {
+  override val name: String
+    get() = FlutterBundle.message("flutter.module.name")
+
+  override fun getIcon(file: VirtualFile): Icon? {
+    return FlutterIcons.Flutter
+  }
+
+  override fun canOpenProject(file: VirtualFile): Boolean {
+    val info = ApplicationInfo.getInstance()
+    if (FlutterUtils.isAndroidStudio()) {
+      return false
+    }
+    val root = PubRoot.forDirectory(file)
+    return root != null && root.declaresFlutter()
+  }
+
+  /**
+   * Replaces the deprecated `doOpenProject`.
+   *
+   * This method is `suspend` and must be used instead of `doOpenProject` to avoid `IllegalStateException` in newer IDE versions.
+   *
+   * It performs the following steps:
+   * 1. Finds a delegate processor (e.g. Gradle) to open the project.
+   * 2. Opens the project asynchronously.
+   * 3. Once opened, checks if the project contains Flutter modules that are not yet configured as such (e.g. missing module type).
+   * 4. Configures these modules as Flutter modules within a write action.
+   */
+  override suspend fun openProjectAsync(
+    virtualFile: VirtualFile,
+    projectToClose: Project?,
+    forceOpenInNewFrame: Boolean,
+  ): Project? {
+    // Delegate opening to the platform open processor.
+    val importProvider = getDelegateImportProvider(virtualFile) ?: return null
+    val project = importProvider.openProjectAsync(virtualFile, projectToClose, forceOpenInNewFrame)
+    if (project == null || project.isDisposed) return project
+
+    // Convert any modules that use Flutter but don't have IntelliJ Flutter metadata.
+    convertToFlutterProject(project)
+
+    return project
+  }
+
+  /**
+   * Deprecated method, kept to satisfy the compiler/interface.
+   *
+   * We return `null` to indicate that this processor does not support the synchronous opening method
+   * and that `openProjectAsync` should be used instead.
+   */
+  override fun doOpenProject(
+    virtualFile: VirtualFile,
+    projectToClose: Project?,
+    forceOpenInNewFrame: Boolean,
+  ): Project? {
+    return null
+  }
+
+  protected open fun getDelegateImportProvider(file: VirtualFile): ProjectOpenProcessor? {
+    return EXTENSION_POINT_NAME.extensionList.stream().filter { processor: ProjectOpenProcessor ->
+      processor.canOpenProject(file) && !Objects.equals(
+        processor.name,
+        name
+      )
+    }.findFirst().orElse(null)
+  }
+
+
+  companion object {
+    /**
+     * Sets up a project that doesn't have any Flutter modules.
+     *
+     *
+     * (It probably wasn't created with "flutter create" and probably didn't have any IntelliJ configuration before.)
+     */
+    private fun convertToFlutterProject(project: Project) {
+      for (module in FlutterModuleUtils.getModules(project)) {
+        if (FlutterModuleUtils.declaresFlutter(module) && !FlutterModuleUtils.isFlutterModule(module)) {
+          FlutterModuleUtils.setFlutterModuleAndReload(module, project)
+        }
+      }
+    }
+  }
+}

src/io/flutter/project/FlutterProjectOpenProcessor.java

@@ -375,13 +375,14 @@ public static void setFlutterModuleType(@NotNull Module module) {
 
   public static void setFlutterModuleAndReload(@NotNull Module module, @NotNull Project project) {
     if (project.isDisposed()) return;
+    ApplicationManager.getApplication().invokeLater(() -> {
+      ApplicationManager.getApplication().runWriteAction(() -> setFlutterModuleType(module));
+      enableDartSDK(module);
+      project.save();
 
-    setFlutterModuleType(module);
-    enableDartSDK(module);
-    project.save();
-
-    EditorNotifications.getInstance(project).updateAllNotifications();
-    ProjectManager.getInstance().reloadProject(project);
+      EditorNotifications.getInstance(project).updateAllNotifications();
+      ProjectManager.getInstance().reloadProject(project);
+    });
   }
 
   public static void enableDartSDK(final @NotNull Module module) {