Allow lazy Cxx modules to not initialize

Reviewed By: mhorowitz

Differential Revision: D4851596

fbshipit-source-id: cf5f5c51b9aaa0da96f7ab6fba1277b72c988400

React/CxxModule/RCTCxxUtils.mm

@@ -46,12 +46,6 @@ std::vector<std::unique_ptr<NativeModule>> createNativeModules(NSArray<RCTModule
   std::vector<std::unique_ptr<NativeModule>> nativeModules;
   for (RCTModuleData *moduleData in modules) {
     if ([moduleData.moduleClass isSubclassOfClass:[RCTCxxModule class]]) {
-      // If a module does not support automatic instantiation, and
-      // wasn't provided as an extra module, it may not have an
-      // instance.  If so, skip it.
-      if (![moduleData hasInstance]) {
-        continue;
-      }
       nativeModules.emplace_back(std::make_unique<CxxNativeModule>(
         instance,
         [moduleData.name UTF8String],

ReactCommon/cxxreact/CxxNativeModule.cpp

@@ -64,6 +64,10 @@ std::vector<MethodDescriptor> CxxNativeModule::getMethods() {
 folly::dynamic CxxNativeModule::getConstants() {
   lazyInit();
 
+  if (!module_) {
+    return nullptr;
+  }
+
   folly::dynamic constants = folly::dynamic::object();
   for (auto& pair : module_->getConstants()) {
     constants.insert(std::move(pair.first), std::move(pair.second));
@@ -161,13 +165,17 @@ MethodCallResult CxxNativeModule::callSerializableNativeHook(
 }
 
 void CxxNativeModule::lazyInit() {
-  if (module_) {
+  if (module_ || !provider_) {
     return;
   }
 
+  // TODO 17216751: providers should never return null modules
   module_ = provider_();
-  methods_ = module_->getMethods();
-  module_->setInstance(instance_);
+  provider_ = nullptr;
+  if (module_) {
+    methods_ = module_->getMethods();
+    module_->setInstance(instance_);
+  }
 }
 
 }

ReactCommon/cxxreact/ModuleRegistry.cpp

@@ -105,7 +105,7 @@ folly::Optional<ModuleConfig> ModuleRegistry::getConfig(const std::string& name)
     }
   }
 
-  if (config.size() == 1) {
+  if (config.size() == 2 && config[1].empty()) {
     // no constants or methods
     return nullptr;
   } else {