Add a separate file for plugin logs (#8253)

This adds a new class `PluginLogger` that prints log messages to a
separate `flutter.log` file. Log messages will continue to print to
`idea.log` also because `PluginLogger` has a parent logger that
continues to log there.

The built in `FileHandler` class manages writing to the file and
removing old lines if the file gets too big.

Author: helin24

.idea/runConfigurations/flutter_intellij__runIde_.xml

@@ -41,6 +41,7 @@
 import io.flutter.devtools.RemainingDevToolsViewFactory;
 import io.flutter.editor.FlutterSaveActionsManager;
 import io.flutter.logging.FlutterConsoleLogManager;
+import io.flutter.logging.PluginLogger;
 import io.flutter.module.FlutterModuleBuilder;
 import io.flutter.pub.PubRoot;
 import io.flutter.pub.PubRoots;
@@ -74,8 +75,7 @@
  * may run when a project is being imported.
  */
 public class FlutterInitializer extends FlutterProjectActivity {
-  private static final @NotNull Logger LOG = Logger.getInstance(FlutterInitializer.class);
-
+  private static final @NotNull Logger LOG = PluginLogger.createLogger(FlutterInitializer.class);
   private boolean toolWindowsInitialized = false;
 
   private boolean busSubscribed = false;
@@ -84,6 +84,7 @@ public class FlutterInitializer extends FlutterProjectActivity {
 
   @Override
   public void executeProjectStartup(@NotNull Project project) {
+    LOG.info("Executing Flutter plugin startup for project: " + project.getName());
     // Disable the 'Migrate Project to Gradle' notification.
     FlutterUtils.disableGradleProjectMigrationNotification(project);
 
@@ -108,6 +109,7 @@ public void executeProjectStartup(@NotNull Project project) {
         continue;
       }
 
+      LOG.info("Flutter module has been found for project: " + project.getName());
       // Ensure SDKs are configured; needed for clean module import.
       FlutterModuleUtils.enableDartSDK(module);
 

flutter-idea/src/io/flutter/FlutterInitializer.java

@@ -0,0 +1,37 @@
+/*
+ * 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.logging;
+
+import com.intellij.openapi.application.PathManager;
+import com.intellij.openapi.diagnostic.Logger;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.logging.FileHandler;
+import java.util.logging.SimpleFormatter;
+
+public class PluginLogger {
+  private static final String LOG_FILE_NAME = "flutter.log";
+  private static final FileHandler fileHandler;
+  static {
+    final String logPath = PathManager.getLogPath();
+    try {
+      fileHandler = new FileHandler(logPath + File.separatorChar + LOG_FILE_NAME, 1024 * 1024, 1);
+    }
+    catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+    System.setProperty("java.util.logging.SimpleFormatter.format",
+                       "%1$tF %1$tT %3$s [%4$-7s] %5$s %6$s %n");
+    fileHandler.setFormatter(new SimpleFormatter());
+  }
+
+  public static Logger createLogger(@NotNull Class<?> logClass) {
+    java.util.logging.Logger.getLogger(logClass.getName()).addHandler(fileHandler);
+    return Logger.getInstance(logClass.getName());
+  }
+}

flutter-idea/src/io/flutter/logging/PluginLogger.java

@@ -38,6 +38,7 @@
 import io.flutter.bazel.Workspace;
 import io.flutter.bazel.WorkspaceCache;
 import io.flutter.dart.DtdUtils;
+import io.flutter.logging.PluginLogger;
 import io.flutter.sdk.FlutterSdk;
 import io.flutter.sdk.FlutterSdkUtil;
 import io.flutter.utils.JsonUtils;
@@ -57,7 +58,7 @@
 import java.util.concurrent.atomic.AtomicReference;
 
 class DevToolsServerTask extends Task.Backgroundable {
-  private @NotNull static final Logger LOG = Logger.getInstance(DevToolsServerTask.class);
+  private @NotNull static final Logger LOG = PluginLogger.createLogger(DevToolsServerTask.class);
   public @NotNull static final String LOCAL_DEVTOOLS_DIR = "flutter.local.devtools.dir";
   public @NotNull static final String LOCAL_DEVTOOLS_ARGS = "flutter.local.devtools.args";
   private @NotNull final Project project;
@@ -79,6 +80,7 @@ public void run(@NotNull ProgressIndicator progressIndicator) {
     try {
       progressIndicator.setFraction(30);
       progressIndicator.setText2("Init");
+      LOG.info("Finding or starting DevTools");
 
       // If we are in a Bazel workspace, start the server.
       // Note: This is only for internal usages.