xplat/js/react-native-github/packages/react-native/ReactAndroid/src/main/jni/react/jni/ModuleRegistryBuilder.cpp (#57457)

Summary: Pull Request resolved: #57457

Reviewed By: cortinico

Differential Revision: D110876914

fbshipit-source-id: 6c65fce7ad97dc31dc8df71925ed1e155bc1109a

Author: generatedunixname1563563004708334

packages/react-native/ReactAndroid/src/main/jni/react/jni/test/ModuleRegistryBuilderTest.cpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <react/jni/ModuleRegistryBuilder.h>
+
+#include <fbjni/fbjni.h>
+#include <gtest/gtest.h>
+
+#include <memory>
+
+#ifndef RCT_REMOVE_LEGACY_ARCH
+
+namespace facebook::react {
+
+/**
+ * Pure-C++ unit tests for the JNI-free slice of `ModuleRegistryBuilder.cpp`.
+ *
+ * The bulk of this translation unit is JNI-coupled: `ModuleHolder::getName`
+ * and `ModuleHolder::getProvider` both call into a live JavaVM (via
+ * `getClass()` / `jni::make_global(self())`), so their behaviour is
+ * exercised by the Robolectric / instrumentation tests that run against a
+ * real JVM.
+ *
+ * The one branch that can be validated host-side without an attached JavaVM
+ * is `buildNativeModuleList`'s null-collection guard: when the incoming
+ * `alias_ref<JCollection<...>>` is a null reference, the function must
+ * short-circuit and return an empty vector rather than dereferencing the
+ * null collection. `alias_ref` is default-constructible to a null state
+ * whose `operator bool()` returns false, which is exactly what
+ * `buildNativeModuleList`'s `if (javaModules)` check tests against, so we
+ * can drive that path without touching JNI.
+ */
+
+/*
+ * Verifies the null-input contract of `buildNativeModuleList`: when the
+ * `javaModules` collection is a null `alias_ref`, no `JavaNativeModule`
+ * instances are constructed and the returned vector is empty.
+ *
+ * Bug this catches: if the `if (javaModules)` guard is ever removed or
+ * inverted, the subsequent `for (const auto& jm : *javaModules)` would
+ * dereference a null JNI reference and crash the process on every startup
+ * path that leaves `javaModules` unset (for example, new-architecture
+ * bring-up paths that legitimately pass no legacy Java modules). Because
+ * the crash would only surface once the process actually reaches this
+ * code with a null collection, catching it here — instead of relying on
+ * a device-side smoke test — is the earliest signal available.
+ *
+ * The `Instance` weak_ptr and `MessageQueueThread` shared_ptr are supplied
+ * as empty on purpose: the guard runs before either is dereferenced, so
+ * their state must not affect the null-collection contract.
+ */
+TEST(
+    ModuleRegistryBuilderTest,
+    buildNativeModuleListReturnsEmptyForNullCollection) {
+  std::weak_ptr<Instance> noInstance;
+  std::shared_ptr<MessageQueueThread> noQueue;
+  jni::alias_ref<jni::JCollection<JavaModuleWrapper::javaobject>::javaobject>
+      nullCollection;
+  ASSERT_FALSE(static_cast<bool>(nullCollection))
+      << "Precondition: default-constructed alias_ref must be null so that "
+         "the guard under test is actually exercised.";
+
+  auto modules = buildNativeModuleList(noInstance, nullCollection, noQueue);
+
+  EXPECT_TRUE(modules.empty());
+}
+
+} // namespace facebook::react
+
+#endif