[vite-plugin] Fail clearly for remote bindings under Bun in v1

.changeset/v1-bun-remote-bindings.md

@@ -0,0 +1,7 @@
+---
+"@cloudflare/vite-plugin": patch
+---
+
+Report unsupported remote bindings under Bun instead of hanging
+
+Starting remote bindings now fails with an actionable error explaining Bun's unsupported request routing. Use Node.js or disable remote bindings to continue local development.

packages/remote-bindings/src/start-remote-proxy-session.test.ts

@@ -57,6 +57,30 @@ function makeErrorEvent(cause: ErrorEvent["cause"]): ErrorEvent {
 }
 
 describe("startRemoteProxySession error handling", () => {
+	it("throws a UserError under Bun before starting the session", async ({
+		expect,
+		onTestFinished,
+	}) => {
+		const originalBunVersion = process.versions.bun;
+		process.versions.bun = "1.4.4";
+		onTestFinished(() => {
+			process.versions.bun = originalBunVersion;
+		});
+
+		const thrown = await startRemoteProxySession(
+			{},
+			{ cliDisplayName: "Test CLI", logger: createTestLogger() }
+		).catch((error: unknown) => error);
+
+		expect(thrown).toBeInstanceOf(UserError);
+		expect(thrown).toMatchObject({
+			message: expect.stringContaining(
+				"https://github.com/oven-sh/bun/issues/39247"
+			),
+			telemetryMessage: "remote proxy session under bun",
+		});
+	});
+
 	// Regression: a `UserError` emitted asynchronously (e.g. the Miniflare
 	// user-error case in `DevEnv.handleErrorEvent`) used to fall through to being
 	// wrapped in a generic `Error`, which makes Wrangler treat it as an

packages/remote-bindings/src/start-remote-proxy-session.ts

@@ -104,6 +104,16 @@ export async function startRemoteProxySession(
 		}
 	}
 
+	// The session hands its local proxy the remote connection in a control
+	// message sent through an undici `dispatcher`, which Bun's `fetch()` ignores,
+	// so every remote binding request would wait forever.
+	if (process.versions.bun) {
+		throw new UserError(
+			"Remote bindings can't work under Bun, because Bun's `fetch()` ignores the undici `dispatcher` that Miniflare routes them through (https://github.com/oven-sh/bun/issues/39247). Run this using Node.js, or turn remote bindings off.",
+			{ telemetryMessage: "remote proxy session under bun" }
+		);
+	}
+
 	options.logger.log(chalk.dim("⎔ Establishing remote connection..."));
 	initLogger(getInternalLogger(options.logger));
 	const rawBindings = toRawBindings(bindings);