From c3821ee730b2da5e225a798d621e1a83450724f8 Mon Sep 17 00:00:00 2001
From: Roman <dev@rman.dev>
Date: Sat, 14 Feb 2026 01:08:24 +0000
Subject: [PATCH] create a plugin for virtual 'usts:runtime' module

---
 packages/usts/package.json              |  3 ++-
 packages/usts/src/core/build/options.ts | 30 ++++++++++++++++++++++---
 packages/usts/src/core/build/watch.ts   |  2 +-
 packages/usts/src/types/virtual.d.ts    |  4 ++++
 packages/usts/tsdown.config.ts          |  9 +++++++-
 5 files changed, 42 insertions(+), 6 deletions(-)
 create mode 100644 packages/usts/src/types/virtual.d.ts

diff --git a/packages/usts/package.json b/packages/usts/package.json
index 3749b42..167e9f3 100644
--- a/packages/usts/package.json
+++ b/packages/usts/package.json
@@ -22,7 +22,8 @@
     "./bin/cli": "./dist/bin/cli.mjs",
     "./config": "./dist/config.mjs",
     "./core": "./dist/core.mjs",
-    "./package.json": "./package.json"
+    "./package.json": "./package.json",
+    "./types": "./virtual.d.ts"
   },
   "bin": {
     "usts": "./dist/bin/cli.mjs"
diff --git a/packages/usts/src/core/build/options.ts b/packages/usts/src/core/build/options.ts
index 1e6eafc..7804530 100644
--- a/packages/usts/src/core/build/options.ts
+++ b/packages/usts/src/core/build/options.ts
@@ -1,8 +1,29 @@
 import * as path from "node:path";
-import type { InputOptions, OutputOptions } from "rolldown";
+import type { InputOptions, OutputOptions, Plugin } from "rolldown";
 import type { ResolvedUserscriptConfig } from "~/config/schema";
 import { serializeMetaHeader } from "./meta-header";
 
+function userscriptPlugin(options?: { dev?: boolean }) {
+  const id = "usts:runtime";
+  const resolvedId = `\0${id}`;
+  return {
+    name: "userscript-plugin",
+    resolveId(source) {
+      if (source === id) {
+        return resolvedId;
+      }
+      return null;
+    },
+    load(id) {
+      if (id === resolvedId) {
+        return `const IS_DEV = ${options?.dev ?? false};
+        export { IS_DEV };`;
+      }
+      return null;
+    },
+  } satisfies Plugin;
+}
+
 interface ResolvedOutputOptions extends OutputOptions {
   readonly file: string;
 }
@@ -15,7 +36,7 @@ interface ResolvedOptions extends InputOptions {
 
 export function resolveOptions(
   config: ResolvedUserscriptConfig,
-  options?: { write?: boolean },
+  options?: { write?: boolean; dev?: boolean },
 ): ResolvedOptions {
   const header = serializeMetaHeader(config.header);
 
@@ -25,7 +46,7 @@ export function resolveOptions(
   return {
     input: config.entryPoint,
     tsconfig: true,
-    plugins: [config.plugins],
+    plugins: [config.plugins, userscriptPlugin({ dev: options?.dev })],
     output: {
       format: "iife",
       sourcemap: false,
@@ -34,6 +55,9 @@ export function resolveOptions(
       cleanDir: config.clean,
       file: outFile,
     },
+    transform: {
+      define: { "process.env.NODE_ENV": `"${process.env.NODE_ENV}"` },
+    },
     write: options?.write ?? false,
   };
 }
diff --git a/packages/usts/src/core/build/watch.ts b/packages/usts/src/core/build/watch.ts
index d649277..485eb1b 100644
--- a/packages/usts/src/core/build/watch.ts
+++ b/packages/usts/src/core/build/watch.ts
@@ -10,7 +10,7 @@ async function watchUserscript(
   options?: { port?: number },
 ): Promise<void> {
   const USERSCRIPT_OUTPUT_FILE_NAME = "index.user.js";
-  const watchOptions = resolveOptions(config);
+  const watchOptions = resolveOptions(config, { dev: true });
   rolldown.watch(watchOptions);
   await serve({
     port: options?.port ?? 3000,
diff --git a/packages/usts/src/types/virtual.d.ts b/packages/usts/src/types/virtual.d.ts
new file mode 100644
index 0000000..5b08b28
--- /dev/null
+++ b/packages/usts/src/types/virtual.d.ts
@@ -0,0 +1,4 @@
+declare module "usts:runtime" {
+  const IS_DEV: boolean;
+  export { IS_DEV };
+}
diff --git a/packages/usts/tsdown.config.ts b/packages/usts/tsdown.config.ts
index e3e8d18..7122e3f 100644
--- a/packages/usts/tsdown.config.ts
+++ b/packages/usts/tsdown.config.ts
@@ -6,7 +6,14 @@ export default defineConfig({
     config: "src/config/index.ts",
     "bin/cli": "src/bin/cli.ts",
   },
-  exports: true,
+  copy: { from: "src/types/*.d.ts", to: "dist" },
+  exports: {
+    enabled: true,
+    customExports(pkg) {
+      pkg["./types"] = "./virtual.d.ts";
+      return pkg;
+    },
+  },
   hash: false,
   outputOptions: { minify: "dce-only", minifyInternalExports: false },
   dts: true,