refactor(core): replace missingBuildHandler() with throwing of new SetupError

src/app.ts

@@ -1,6 +1,5 @@
 import * as path from "@std/path";
-import { type ComponentType, h } from "preact";
-import { renderToString } from "preact-render-to-string";
+import type { ComponentType } from "preact";
 import { trace } from "@opentelemetry/api";
 
 import { DENO_DEPLOYMENT_ID } from "./runtime/build_id.ts";
@@ -15,8 +14,7 @@ import {
 } from "./config.ts";
 import { type BuildCache, ProdBuildCache } from "./build_cache.ts";
 import type { ServerIslandRegistry } from "./context.ts";
-import { FinishSetup, ForgotBuild } from "./finish_setup.tsx";
-import { HttpError } from "./error.ts";
+import { HttpError, SetupError } from "./error.ts";
 import { mergePaths } from "./utils.ts";
 
 // TODO: Completed type clashes in older Deno versions
@@ -254,11 +252,14 @@ export class App<State> {
       );
     }
 
-    if (
-      !this.#buildCache.hasSnapshot && this.config.mode === "production" &&
-      DENO_DEPLOYMENT_ID !== undefined
-    ) {
-      return missingBuildHandler;
+    if (!this.#buildCache.hasSnapshot && this.config.mode === "production") {
+      let message =
+        "The build cache is not set up. Run `deno task build` before starting the server.";
+      if (DENO_DEPLOYMENT_ID !== undefined) {
+        message +=
+          ' Go to "Settings" in Deno Deploy and set the build command to `deno task build`.';
+      }
+      throw new SetupError(message);
     }
 
     return async (
@@ -338,14 +339,3 @@ export class App<State> {
     await listenOnFreePort(options, handler);
   }
 }
-
-// deno-lint-ignore require-await
-const missingBuildHandler = async (): Promise<Response> => {
-  const headers = new Headers();
-  headers.set("Content-Type", "text/html; charset=utf-8");
-
-  const html = DENO_DEPLOYMENT_ID
-    ? renderToString(h(FinishSetup, null))
-    : renderToString(h(ForgotBuild, null));
-  return new Response(html, { headers, status: 500 });
-};

src/error.ts

@@ -74,3 +74,26 @@ export class HttpError extends Error {
     this.status = status;
   }
 }
+
+/**
+ * Error that's throw when the app setup fails. Usually caused by
+ * `deno task build` not being run before starting the server.
+ *
+ * @example Basic usage
+ * ```ts ignore
+ * import { App, SetupError } from "fresh";
+ * import { expect } from "@std/expect";
+ *
+ * const app = new App()
+ *   .get("/", () => new Response("ok"))
+ *
+ * try {
+ *   // Throws if `deno task build` was not run beforehand
+ *   const handler = await app.handler();
+ * } catch (error) {
+ *   expect(error).toBeInstanceOf(SetupError);
+ *   expect(error.message).toBe("App not setup");
+ * }
+ * ```
+ */
+export class SetupError extends Error {}

tests/fixture_precompile/valid/main.tsx

@@ -1,4 +1,7 @@
 import { App } from "../../../src/app.ts";
+import { Builder } from "../../../src/dev/mod.ts";
+
+const builder = new Builder();
 
 const app = new App({ staticDir: "./static" }).get(
   "/",
@@ -25,6 +28,8 @@ const app = new App({ staticDir: "./static" }).get(
     ),
 );
 
+await builder.build(app);
+
 const handler = app.handler();
 const res = await handler(new Request("http://localhost/"));
 // deno-lint-ignore no-console