fix: prevent vitest from hanging (#12830)

fixes #12305
closes #12306

This is an alternative to #12306 . Instead of creating the emulator every time the Vite dev and preview middlewares are invoked, we await Cloudflare's platform proxy only when the adapter emulated platform is accessed, rather than much earlier when adapter.adapt is invoked.

Author: teemingc

.changeset/six-goats-ring.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-cloudflare': patch
+---
+
+fix: prevent vitest from hanging

packages/adapter-cloudflare-workers/index.js

@@ -149,29 +149,35 @@ export default function ({ config = 'wrangler.toml', platformProxy = {} } = {})
 			builder.writePrerendered(bucket_dir);
 		},
 
-		async emulate() {
-			const proxy = await getPlatformProxy(platformProxy);
-			const platform = /** @type {App.Platform} */ ({
-				env: proxy.env,
-				context: proxy.ctx,
-				caches: proxy.caches,
-				cf: proxy.cf
-			});
+		emulate() {
+			// we want to invoke `getPlatformProxy` only once, but await it only when it is accessed.
+			// If we would await it here, it would hang indefinitely because the platform proxy only resolves once a request happens
+			const getting_platform = (async () => {
+				const proxy = await getPlatformProxy(platformProxy);
+				const platform = /** @type {App.Platform} */ ({
+					env: proxy.env,
+					context: proxy.ctx,
+					caches: proxy.caches,
+					cf: proxy.cf
+				});
 
-			/** @type {Record<string, any>} */
-			const env = {};
-			const prerender_platform = /** @type {App.Platform} */ (/** @type {unknown} */ ({ env }));
+				/** @type {Record<string, any>} */
+				const env = {};
+				const prerender_platform = /** @type {App.Platform} */ (/** @type {unknown} */ ({ env }));
 
-			for (const key in proxy.env) {
-				Object.defineProperty(env, key, {
-					get: () => {
-						throw new Error(`Cannot access platform.env.${key} in a prerenderable route`);
-					}
-				});
-			}
+				for (const key in proxy.env) {
+					Object.defineProperty(env, key, {
+						get: () => {
+							throw new Error(`Cannot access platform.env.${key} in a prerenderable route`);
+						}
+					});
+				}
+				return { platform, prerender_platform };
+			})();
 
 			return {
-				platform: ({ prerender }) => {
+				platform: async ({ prerender }) => {
+					const { platform, prerender_platform } = await getting_platform;
 					return prerender ? prerender_platform : platform;
 				}
 			};

packages/adapter-cloudflare/index.js

@@ -67,29 +67,35 @@ export default function (options = {}) {
 				}
 			});
 		},
-		async emulate() {
-			const proxy = await getPlatformProxy(options.platformProxy);
-			const platform = /** @type {App.Platform} */ ({
-				env: proxy.env,
-				context: proxy.ctx,
-				caches: proxy.caches,
-				cf: proxy.cf
-			});
+		emulate() {
+			// we want to invoke `getPlatformProxy` only once, but await it only when it is accessed.
+			// If we would await it here, it would hang indefinitely because the platform proxy only resolves once a request happens
+			const getting_platform = (async () => {
+				const proxy = await getPlatformProxy(options.platformProxy);
+				const platform = /** @type {App.Platform} */ ({
+					env: proxy.env,
+					context: proxy.ctx,
+					caches: proxy.caches,
+					cf: proxy.cf
+				});
 
-			/** @type {Record<string, any>} */
-			const env = {};
-			const prerender_platform = /** @type {App.Platform} */ (/** @type {unknown} */ ({ env }));
+				/** @type {Record<string, any>} */
+				const env = {};
+				const prerender_platform = /** @type {App.Platform} */ (/** @type {unknown} */ ({ env }));
 
-			for (const key in proxy.env) {
-				Object.defineProperty(env, key, {
-					get: () => {
-						throw new Error(`Cannot access platform.env.${key} in a prerenderable route`);
-					}
-				});
-			}
+				for (const key in proxy.env) {
+					Object.defineProperty(env, key, {
+						get: () => {
+							throw new Error(`Cannot access platform.env.${key} in a prerenderable route`);
+						}
+					});
+				}
+				return { platform, prerender_platform };
+			})();
 
 			return {
-				platform: ({ prerender }) => {
+				platform: async ({ prerender }) => {
+					const { platform, prerender_platform } = await getting_platform;
 					return prerender ? prerender_platform : platform;
 				}
 			};