Adding rust wrapper lib for libfakeServiceManager

rust lib which setup libfakeservicemanager and sets it as default
is being added here. It uses c++ backend underneath.

Test: m libfakeservicemanager_rs
Test: atest fakeservicemanager_test
Bug: 296909761
Change-Id: Ia1e7ebe5174f05fb4f8673a2feaad9b1171eb60c
diff --git a/libs/fakeservicemanager/FakeServiceManager.cpp b/libs/fakeservicemanager/FakeServiceManager.cpp
index 80661c1..241c866 100644
--- a/libs/fakeservicemanager/FakeServiceManager.cpp
+++ b/libs/fakeservicemanager/FakeServiceManager.cpp
@@ -16,6 +16,10 @@
 
 #include "fakeservicemanager/FakeServiceManager.h"
 
+using android::sp;
+using android::FakeServiceManager;
+using android::setDefaultServiceManager;
+
 namespace android {
 
 FakeServiceManager::FakeServiceManager() {}
@@ -123,3 +127,24 @@
     mNameToService.clear();
 }
 }  // namespace android
+
+[[clang::no_destroy]] static sp<FakeServiceManager> gFakeServiceManager;
+[[clang::no_destroy]] static std::once_flag gSmOnce;
+
+extern "C" {
+
+// Setup FakeServiceManager to mock dependencies in test using this API for rust backend
+void setupFakeServiceManager() {
+    /* Create a FakeServiceManager instance and add required services */
+    std::call_once(gSmOnce, [&]() {
+        gFakeServiceManager = new FakeServiceManager();
+        android::setDefaultServiceManager(gFakeServiceManager);
+    });
+}
+
+// Clear existing services from Fake SM for rust backend
+void clearFakeServiceManager() {
+    LOG_ALWAYS_FATAL_IF(gFakeServiceManager == nullptr, "Fake Service Manager is not available. Forgot to call setupFakeServiceManager?");
+    gFakeServiceManager->clear();
+}
+} //extern "C"
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