Basic FS watcher for --load-mod mods

Add a --watch command line flag to be used in tandem with --load-mod.
Chokidar is used to detect file updates, and a page reload is triggered
when there are any changes to watched mod files. Only mods loaded via
--load-mod are affected.

This implementation has a minor issue with how cache is cleared -
removing disk cache is a bit too aggressive - but the only alternative I
could find is to use a non-persistent Electron session, which would get
rid of disk cache entirely (this is not a concern).

electron/package-lock.json

@@ -9,6 +9,7 @@
             "version": "1.0.0",
             "license": "MIT",
             "dependencies": {
+                "chokidar": "^4.0.3",
                 "semver": "^7.7.1",
                 "zod": "^3.24.2"
             },
@@ -192,6 +193,21 @@
                 "node": ">=8"
             }
         },
+        "node_modules/chokidar": {
+            "version": "4.0.3",
+            "resolved": "https://registry.npmjs.org/chokidar/-/chokidar-4.0.3.tgz",
+            "integrity": "sha512-Qgzu8kfBvo+cA4962jnP1KkS6Dop5NS6g7R5LFYJr4b8Ub94PPQXUksCw9PvXoeXPRRddRNC5C1JQUR2SMGtnA==",
+            "license": "MIT",
+            "dependencies": {
+                "readdirp": "^4.0.1"
+            },
+            "engines": {
+                "node": ">= 14.16.0"
+            },
+            "funding": {
+                "url": "https://paulmillr.com/funding/"
+            }
+        },
         "node_modules/clone-response": {
             "version": "1.0.3",
             "resolved": "https://registry.npmjs.org/clone-response/-/clone-response-1.0.3.tgz",
@@ -733,6 +749,19 @@
                 "url": "https://github.com/sponsors/sindresorhus"
             }
         },
+        "node_modules/readdirp": {
+            "version": "4.1.2",
+            "resolved": "https://registry.npmjs.org/readdirp/-/readdirp-4.1.2.tgz",
+            "integrity": "sha512-GDhwkLfywWL2s6vEjyhri+eXmfH6j1L7JE27WhqLeYzoh/A3DBaYGEj2H/HFZCn/kMfim73FXxEJTw06WtxQwg==",
+            "license": "MIT",
+            "engines": {
+                "node": ">= 14.18.0"
+            },
+            "funding": {
+                "type": "individual",
+                "url": "https://paulmillr.com/funding/"
+            }
+        },
         "node_modules/resolve-alpn": {
             "version": "1.2.1",
             "resolved": "https://registry.npmjs.org/resolve-alpn/-/resolve-alpn-1.2.1.tgz",

electron/package.json

@@ -9,6 +9,7 @@
         "start": "tsc && electron ."
     },
     "dependencies": {
+        "chokidar": "^4.0.3",
         "semver": "^7.7.1",
         "zod": "^3.24.2"
     },

electron/src/index.ts

@@ -56,6 +56,12 @@ function createWindow() {
     ipc.install(window);
     window.loadURL(pageUrl);
 
+    modLoader.on("forcereload", () => {
+        // TODO: Find a better way to manage cache when force
+        // reloading (use a non-persistent session?)
+        window.webContents.session.clearData({ dataTypes: ["cache"] }).then(() => window.reload());
+    });
+
     // Redirect any kind of main frame navigation to external applications
     window.webContents.on("will-navigate", (ev, url) => {
         if (url === window.webContents.getURL()) {

electron/src/mods/loader.ts

@@ -1,3 +1,4 @@
+import EventEmitter from "node:events";
 import fs from "node:fs/promises";
 import path from "node:path";
 import { DevelopmentModLocator, DistroModLocator, ModLocator, UserModLocator } from "./locator.js";
@@ -48,14 +49,29 @@ class Mod {
     }
 }
 
-export class ModLoader {
+export class ModLoader extends EventEmitter {
     private mods: Mod[] = [];
     private readonly locators = new Map<ModSource, ModLocator>();
 
     constructor() {
+        super();
+
         this.locators.set("user", new UserModLocator());
         this.locators.set("distro", new DistroModLocator());
-        this.locators.set("dev", new DevelopmentModLocator());
+
+        const devLocator = new DevelopmentModLocator();
+        this.locators.set("dev", devLocator);
+
+        // If requested, restart automatically when dev mods are modified
+        devLocator.fsWatcher?.on("all", () => this.forceReload());
+    }
+
+    /**
+     * Resets modloader state and reloads all mods, then triggers page reload.
+     */
+    async forceReload() {
+        await this.loadMods();
+        this.emit("forcereload");
     }
 
     async loadMods(): Promise<void> {

electron/src/mods/locator.ts

@@ -1,3 +1,4 @@
+import chokidar, { FSWatcher } from "chokidar";
 import { app } from "electron";
 import fs from "node:fs/promises";
 import path from "node:path";
@@ -10,6 +11,7 @@ const USER_MODS_DIR = path.join(userData, "mods");
 const DISTRO_MODS_DIR = path.join(executableDir, "mods");
 
 const DEV_SWITCH = "load-mod";
+const DEV_WATCH_SWITCH = "watch";
 const DEV_USER_MOD_PREFIX = "@/";
 
 export interface ModLocator {
@@ -153,6 +155,7 @@ export class DistroModLocator extends DirectoryModLocator {
 
 export class DevelopmentModLocator implements ModLocator {
     readonly priority = 0;
+    readonly fsWatcher: FSWatcher | null = null;
 
     private readonly modFiles: string[] = [];
     private readonly disabledMods = new Set<string>();
@@ -166,6 +169,19 @@ export class DevelopmentModLocator implements ModLocator {
 
         const resolved = switchValue.split(",").map(f => this.resolveFile(f));
         this.modFiles.push(...resolved);
+
+        const watchMode = app.commandLine.hasSwitch(DEV_WATCH_SWITCH);
+        if (!watchMode || this.modFiles.length === 0) {
+            // Skip setting up chokidar
+            return;
+        }
+
+        this.fsWatcher = chokidar.watch(this.modFiles, {
+            persistent: false,
+            ignoreInitial: true,
+            awaitWriteFinish: true,
+            atomic: true,
+        });
     }
 
     locateMods(): Promise<string[]> {