[wrangler] Add wrangler compile for self-hosting Workers on standalone workerd

.changeset/standalone-compile.md

@@ -0,0 +1,36 @@
+---
+"wrangler": minor
+"miniflare": minor
+"@cloudflare/vite-plugin": minor
+---
+
+Add an experimental `wrangler compile` command (and Vite `standalone` mode) for self-hosting Workers on standalone `workerd`
+
+`wrangler compile` builds your Worker into a self-contained `workerd` bundle (a `config.capnp`, embedded modules, on-disk static assets, a version-pinned `Dockerfile`, an entrypoint, and a `README.md` with run instructions) that you can run on any server outside of Cloudflare. Static assets are wired up out of the box. Pass `--serve` to run the emitted bundle locally with the bundled `workerd` binary — the exact artifact that ships. Pass `--format binary` to emit a single self-contained `config.bin` instead of the human-readable `config.capnp` plus embedded module files.
+
+You can also set `"standalone": true` in your configuration (or pass `--standalone` to `wrangler dev`) to opt in. When set, `wrangler dev` warns about bindings that work locally but are not yet supported by standalone `workerd`, and `wrangler deploy` errors (since the Worker targets a self-hosted runtime rather than Cloudflare).
+
+For Vite projects, pass `standalone: true` to the `cloudflare()` plugin and `vite build` will also emit the same standalone bundle:
+
+```ts
+// vite.config.ts
+import { cloudflare } from "@cloudflare/vite-plugin";
+import { defineConfig } from "vite";
+
+export default defineConfig({
+	plugins: [cloudflare({ standalone: true })],
+});
+```
+
+```jsonc
+// wrangler.json
+{
+	"name": "my-worker",
+	"main": "src/index.js",
+	"compatibility_date": "2025-05-01",
+	"standalone": true,
+	"assets": { "directory": "./public", "binding": "ASSETS" },
+}
+```
+
+This is experimental and currently targets stateless Workers plus static assets; stateful bindings (KV, R2, D1, Durable Objects, etc.) are not yet supported.

packages/miniflare/src/index.ts

@@ -980,6 +980,10 @@ export class Miniflare {
 	readonly #runtime?: Runtime;
 	readonly #removeExitHook?: () => void;
 	#runtimeEntryURL?: URL;
+	// The most recent `workerd` config assembled by `#assembleAndUpdateConfig()`.
+	// Exposed (alpha) via `unstable_getConfig()` so tooling (e.g. `wrangler compile`)
+	// can transform it into a standalone bundle without re-deriving the service graph.
+	#lastAssembledConfig?: Config;
 	publicUrl?: string;
 	#socketPorts?: SocketPorts;
 	#runtimeDispatcher?: Dispatcher;
@@ -2415,6 +2419,7 @@ export class Miniflare {
 			loopbackPort,
 			this.#devRegistry.isEnabled()
 		);
+		this.#lastAssembledConfig = config;
 		const configBuffer = serializeConfig(config);
 
 		// Get all socket names we expect to get ports for
@@ -2663,6 +2668,26 @@ export class Miniflare {
 		return new URL(this.#runtimeEntryURL.toString());
 	}
 
+	/**
+	 * Returns the `workerd` {@link Config} most recently assembled for this
+	 * instance, waiting for initialisation to complete first.
+	 *
+	 * This is an alpha API intended for tooling that needs the fully-resolved
+	 * service graph (e.g. `wrangler compile`, which transforms it into a
+	 * standalone bundle via {@link toStandaloneConfig}). The shape is not yet
+	 * stable and may change without notice.
+	 */
+	async unstable_getConfig(): Promise<Config> {
+		this.#checkDisposed();
+		await this.#initPromise;
+		await this.#runtimeMutex.drained();
+		assert(
+			this.#lastAssembledConfig !== undefined,
+			"Config has not been assembled yet"
+		);
+		return this.#lastAssembledConfig;
+	}
+
 	async #registerWorkers(): Promise<void> {
 		if (!this.#devRegistry.isEnabled()) {
 			return;
@@ -3235,6 +3260,7 @@ export * from "./http";
 export * from "./plugins";
 export * from "./runtime";
 export * from "./shared";
+export * from "./standalone";
 export * from "./workers";
 export * from "./merge";
 export * from "./zod-format";