Warn when someone downgrades across dataVersion boundaries

src-main/l10n/en.json

@@ -287,6 +287,18 @@
     "string": "Deleting old data...",
     "developer_comment": "Status message that appears while finishing an update. Old data refers to data stored by old versions of the app that is now redundant after updates."
   },
+  "migrate-future.message": {
+    "string": "It looks like you installed an older version of {APP_NAME} after using a later version. Downgrading is not guaranteed to be safe; you may lose data such as your settings and backpack. Please exit and download the latest version from {website}. (Debug info: {debugInfo})",
+    "developer_comment": "May appear when someone installs the latest version of the dekstop app, runs it, then installs and runs an older version. {APP_NAME} becomes 'TurboWarp Desktop'. {website} becomes a URL like 'desktop.turbowarp.org'. {debugInfo} becomes something like '2 < 3' (internal version numbers) to aid with debugging."
+  },
+  "migrate-future.exit": {
+    "string": "Exit and Update",
+    "developer_comment": "May appear when someone installs the latest version of the dekstop app, runs it, then installs and runs an older version. This button exits the app and opens the website for someone to download the latest version."
+  },
+  "migrate-future.continue-anyways": {
+    "string": "Continue Anyways (Unsafe)",
+    "developer_comment": "May appear when someone installs the latest version of the dekstop app, runs it, then installs and runs an older version. This button accepts the warning and will just continue anyways, hoping for the best."
+  },
   "update.window-title": {
     "string": "Update Available",
     "developer_comment": "Title of update available window"

src-main/migrate.js

@@ -1,8 +1,11 @@
-const {app} = require('electron');
+const {app, dialog} = require('electron');
 const fs = require('fs');
 const path = require('path');
 const settings = require('./settings');
 const MigrateWindow = require('./windows/migrate');
+const {APP_NAME} = require('./brand');
+const {translate} = require('./l10n');
+const safelyOpenExternal = require('./open-external');
 
 // Avoid running migrate logic on fresh installs when we can. Not required, just helps
 // user experience. This must run before the ready event.
@@ -14,6 +17,32 @@ const isFirstLaunch = (
 );
 
 const migrate = async () => {
+  if (settings.dataVersion > MigrateWindow.LATEST_VERSION) {
+    const result = dialog.showMessageBoxSync({
+      type: 'error',
+      title: APP_NAME,
+      message: translate('migrate-future.message')
+        .replace('{APP_NAME}', APP_NAME)
+        .replace('{website}', 'desktop.turbowarp.org')
+        .replace('{debugInfo}', `${MigrateWindow.LATEST_VERSION} < ${settings.dataVersion}`),
+      buttons: [
+        translate('migrate-future.exit'),
+        translate('migrate-future.continue-anyways')
+      ],
+      cancelId: 0,
+      defaultId: 0
+    });
+    if (result === 0) {
+      safelyOpenExternal('https://desktop.turbowarp.org/');
+      app.exit(1);
+    } else {
+      // Hope for the best!
+      settings.dataVersion = MigrateWindow.LATEST_VERSION;
+      await settings.save();
+      return;
+    }
+  }
+
   if (settings.dataVersion === MigrateWindow.LATEST_VERSION) {
     return;
   }

src-main/windows/migrate.js

@@ -8,7 +8,7 @@ const {APP_NAME} = require('../brand');
 const EMAIL = '[email protected]';
 
 class MigrateWindow extends BaseWindow {
-  static LATEST_VERSION = 3;
+  static LATEST_VERSION = 2;
 
   constructor () {
     super();