From cfff797f03300805e045ebbe010c61fad8ab11fc Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 3 Dec 2025 19:11:11 +0000
Subject: [PATCH 1/2] Initial plan


From 9a35a69178bb3355c912d31b2d3f040c32070f21 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 3 Dec 2025 19:20:23 +0000
Subject: [PATCH 2/2] fix: Write last-install.flag after update-autoinstaller
 completes

Co-authored-by: iclanton <5010588+iclanton@users.noreply.github.com>
---
 libraries/rush-lib/src/logic/Autoinstaller.ts | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/libraries/rush-lib/src/logic/Autoinstaller.ts b/libraries/rush-lib/src/logic/Autoinstaller.ts
index 8c35ea07b8..84fb06f243 100644
--- a/libraries/rush-lib/src/logic/Autoinstaller.ts
+++ b/libraries/rush-lib/src/logic/Autoinstaller.ts
@@ -265,6 +265,44 @@ export class Autoinstaller {
     } else {
       this._logIfConsoleOutputIsNotRestricted(Colorize.green('Already up to date.'));
     }
+
+    // Write the last-install.flag file so that a subsequent "rush install-autoinstaller"
+    // will not perform a redundant install.
+    await this._createFlagsAsync();
+  }
+
+  private async _createFlagsAsync(): Promise<void> {
+    const autoinstallerFullPath: string = this.folderFullPath;
+
+    // Example: .../common/autoinstallers/my-task/.rush/temp
+    const lastInstallFlagPath: string = path.join(
+      autoinstallerFullPath,
+      RushConstants.projectRushFolderName,
+      'temp'
+    );
+
+    const packageJsonPath: string = path.join(autoinstallerFullPath, 'package.json');
+    const packageJson: IPackageJson = JsonFile.load(packageJsonPath);
+
+    const lastInstallFlag: LastInstallFlag = new LastInstallFlag(lastInstallFlagPath, {
+      node: process.versions.node,
+      packageManager: this._rushConfiguration.packageManager,
+      packageManagerVersion: this._rushConfiguration.packageManagerToolVersion,
+      packageJson: packageJson,
+      rushJsonFolder: this._rushConfiguration.rushJsonFolder
+    });
+
+    // Create file: ../common/autoinstallers/my-task/.rush/temp/last-install.flag
+    await lastInstallFlag.createAsync();
+
+    // Example: ../common/autoinstallers/my-task/node_modules
+    const nodeModulesFolder: string = `${autoinstallerFullPath}/${RushConstants.nodeModulesFolderName}`;
+    const flagPath: string = `${nodeModulesFolder}/rush-autoinstaller.flag`;
+
+    FileSystem.writeFile(
+      flagPath,
+      'If this file is deleted, Rush will assume that the node_modules folder has been cleaned and will reinstall it.'
+    );
   }
 
   private _logIfConsoleOutputIsNotRestricted(message?: string): void {