feat: add watch mode

Author: gameroman

package.json

@@ -29,6 +29,7 @@
     "format": "biome check --write --linter-enabled=false",
     "build:app": "bun run --cwd ./apps/registry build",
     "build:cli": "bun run --cwd ./packages/usts build",
+    "build": "bun run build:cli",
     "test": "bun run --cwd ./packages/usts test"
   },
   "devDependencies": {

packages/usts/src/cli/build/index.ts

@@ -1,7 +1,8 @@
 import { resolveConfig } from "~/config/resolve";
 import { buildUserscript } from "~/core/build";
+import { watchUserscript } from "~/core/build/watch";
 
-async function build(): Promise<void> {
+async function build(options: { watch?: boolean }): Promise<void> {
   const { userscriptConfig, root } = await resolveConfig();
 
   const outDir = userscriptConfig.outDir;
@@ -12,7 +13,13 @@ async function build(): Promise<void> {
     );
   }
 
-  await buildUserscript(userscriptConfig, { write: true });
+  if (!options.watch) {
+    await buildUserscript(userscriptConfig, { write: true });
+  }
+
+  if (options.watch) {
+    watchUserscript(userscriptConfig);
+  }
 }
 
 export { build };

packages/usts/src/cli/index.ts

@@ -2,15 +2,25 @@ import { parseArgs } from "node:util";
 
 type CLICommand = "help" | "build";
 
-type Flags = {} & Record<string, never>;
+type Flags = { watch: boolean };
 
 interface Args {
   values: Flags;
   positionals: string[];
 }
 
 async function printHelp() {
-  console.log("Run `usts build` to build a userscript");
+  console.log(`
+usts build - build a userscript
+usts build --watch - build userscript in watch mode
+`);
+}
+
+function isSupportedCommand<T extends CLICommand>(
+  supportedCommands: T[],
+  cmd: string,
+): cmd is T {
+  return new Set<string>(supportedCommands).has(cmd);
 }
 
 function resolveCommand(parsedArgs: Args): CLICommand {
@@ -20,30 +30,33 @@ function resolveCommand(parsedArgs: Args): CLICommand {
     return "help";
   }
 
-  const supportedCommands = new Set(["build"]);
-  if (supportedCommands.has(cmd)) {
-    return cmd as CLICommand;
+  if (isSupportedCommand(["build"], cmd)) {
+    return cmd;
   }
 
   return "help";
 }
 
-async function runCommand(cmd: CLICommand) {
+async function runCommand(cmd: CLICommand, flags: Flags) {
   switch (cmd) {
     case "help": {
       await printHelp();
       return;
     }
     case "build": {
       const { build } = await import("./build/index.js");
-      await build();
+      await build({ watch: flags.watch });
       return;
     }
   }
 }
 
 export async function cli(argv: string[]): Promise<void> {
-  const parsedArgs = parseArgs({ args: argv, allowPositionals: true });
+  const parsedArgs = parseArgs({
+    args: argv,
+    allowPositionals: true,
+    options: { watch: { type: "boolean", default: false } },
+  });
   const cmd = resolveCommand(parsedArgs);
-  await runCommand(cmd);
+  await runCommand(cmd, parsedArgs.values);
 }

packages/usts/src/core/build/index.ts

@@ -1,34 +1,14 @@
-import * as path from "node:path";
-
 import * as rolldown from "rolldown";
 
 import type { ResolvedUserscriptConfig } from "~/config/schema";
 
-import { serializeMetaHeader } from "./meta-header";
+import { resolveOptions } from "./options";
 
 async function buildUserscript(
   config: ResolvedUserscriptConfig,
-  options?: { write?: boolean; watch?: boolean },
+  options?: { write?: boolean },
 ): Promise<string> {
-  const header = serializeMetaHeader(config.header);
-
-  const USERSCRIPT_OUTPUT_FILE_NAME = "index.user.js";
-  const outFile = path.join(config.outDir, USERSCRIPT_OUTPUT_FILE_NAME);
-
-  const result = await rolldown.build({
-    input: config.entryPoint,
-    tsconfig: true,
-    plugins: [config.plugins],
-    output: {
-      format: "iife",
-      sourcemap: false,
-      minify: "dce-only",
-      postBanner: `${header}\n`,
-      cleanDir: config.clean,
-      file: outFile,
-    },
-    write: options?.write ?? false,
-  });
+  const result = await rolldown.build(resolveOptions(config, options));
 
   if (result.output.length !== 1) {
     throw new Error(`❌ Unexpected userscript build output`);

packages/usts/src/core/build/options.ts

@@ -0,0 +1,29 @@
+import * as path from "node:path";
+import type { BuildOptions } from "rolldown";
+import type { ResolvedUserscriptConfig } from "~/config/schema";
+import { serializeMetaHeader } from "./meta-header";
+
+export function resolveOptions(
+  config: ResolvedUserscriptConfig,
+  options?: { write?: boolean },
+): BuildOptions {
+  const header = serializeMetaHeader(config.header);
+
+  const USERSCRIPT_OUTPUT_FILE_NAME = "index.user.js";
+  const outFile = path.join(config.outDir, USERSCRIPT_OUTPUT_FILE_NAME);
+
+  return {
+    input: config.entryPoint,
+    tsconfig: true,
+    plugins: [config.plugins],
+    output: {
+      format: "iife",
+      sourcemap: false,
+      minify: "dce-only",
+      postBanner: `${header}\n`,
+      cleanDir: config.clean,
+      file: outFile,
+    },
+    write: options?.write ?? false,
+  };
+}

packages/usts/src/core/build/watch.ts

@@ -0,0 +1,12 @@
+import * as rolldown from "rolldown";
+
+import type { ResolvedUserscriptConfig } from "~/config/schema";
+
+import { resolveOptions } from "./options";
+
+function watchUserscript(config: ResolvedUserscriptConfig): void {
+  const options = resolveOptions(config);
+  rolldown.watch(options);
+}
+
+export { watchUserscript };