Validate mock.module() first argument is a string

src/bun.js/bindings/BunPlugin.cpp

@@ -511,6 +511,11 @@ extern "C" JSC_DEFINE_HOST_FUNCTION(JSMock__jsModuleMock, (JSC::JSGlobalObject *
         return {};
     }
 
+    if (!callframe->argument(0).isString()) {
+        scope.throwException(lexicalGlobalObject, JSC::createTypeError(lexicalGlobalObject, "mock(module, fn) requires a module name string"_s));
+        return {};
+    }
+
     JSC::JSString* specifierString = callframe->argument(0).toString(globalObject);
     RETURN_IF_EXCEPTION(scope, {});
     WTF::String specifier = specifierString->value(globalObject);

test/js/bun/test/mock/mock-module-non-string.test.ts

@@ -0,0 +1,14 @@
+import { expect, mock, test } from "bun:test";
+
+test("mock.module throws TypeError for non-string first argument", () => {
+  expect(() => mock.module(SharedArrayBuffer, () => ({}))).toThrow("mock(module, fn) requires a module name string");
+  expect(() => mock.module({}, () => ({}))).toThrow("mock(module, fn) requires a module name string");
+  expect(() => mock.module(123, () => ({}))).toThrow("mock(module, fn) requires a module name string");
+  expect(() => mock.module(Symbol("test"), () => ({}))).toThrow("mock(module, fn) requires a module name string");
+});
+
+test("mock.module still works with valid string argument", async () => {
+  mock.module("mock-module-non-string-test-fixture", () => ({ default: 42 }));
+  const m = await import("mock-module-non-string-test-fixture");
+  expect(m.default).toBe(42);
+});