Allow missing parent script with mounted workers

Author: mrbbot

packages/core/src/index.ts

@@ -430,14 +430,6 @@ export class MiniflareCore<
     // changes
     this.#previousOptions = options;
 
-    // Make sure we've got a script if it's required
-    if (
-      this.#ctx.scriptRequired &&
-      !this.#setupResults.get("CorePlugin")?.script
-    ) {
-      throwNoScriptError(options.CorePlugin.modules);
-    }
-
     // Update mounts
     this.#mounts ??= new Map();
     const mounts = options.CorePlugin
@@ -543,6 +535,16 @@ export class MiniflareCore<
       }
     }
     await this.#updateRouter();
+
+    // Make sure we've got a script if it's required (if we've got mounts,
+    // allow no script, as we might always route to those)
+    if (
+      this.#ctx.scriptRequired &&
+      !this.#setupResults.get("CorePlugin")?.script &&
+      this.#mounts.size === 0
+    ) {
+      throwNoScriptError(options.CorePlugin.modules);
+    }
   }
 
   async #updateRouter(): Promise<void> {

packages/core/test/index.mounts.spec.ts

@@ -9,6 +9,7 @@ import {
   BindingsPlugin,
   CorePlugin,
   MiniflareCore,
+  MiniflareCoreContext,
   MiniflareCoreError,
   ReloadEvent,
 } from "@miniflare/core";
@@ -319,6 +320,20 @@ test("MiniflareCore: #init: disposes removed mounts", async (t) => {
   res = await mf.dispatchFetch("http://localhost/b");
   t.is(await res.text(), "b");
 });
+test("MiniflareCore: #init: doesn't throw if script required, parent script not provided, but has mounts", async (t) => {
+  const ctx: MiniflareCoreContext = {
+    log: new NoOpLog(),
+    storageFactory: new MemoryStorageFactory(),
+    scriptRunner: new VMScriptRunner(),
+    scriptRequired: true,
+  };
+
+  const mf = new MiniflareCore({ CorePlugin }, ctx, {
+    mounts: { a: { script: constantBodyScript("a") } },
+  });
+  await mf.getPlugins();
+  t.pass();
+});
 
 test("MiniflareCore: #reload: includes mounted module exports when calling plugin reload hooks", async (t) => {
   const mf = useMiniflare(