iOS: register lazy nativemodules on startup when Chrome is attached

Summary:
@public
This allows apps to specify custom lazy modules that they need to load during chrome debugging. This is because lazy modules won't be available on start up, hence these modules will be missing in JS land, causing problems.

Reviewed By: shergin

Differential Revision: D12899408

fbshipit-source-id: dca313648e994b22e3ee5afec856ef76470065f9

React/Base/RCTBridgeDelegate.h

@@ -72,4 +72,9 @@
 - (void)loadSourceForBridge:(RCTBridge *)bridge
                   withBlock:(RCTSourceLoadBlock)loadCallback;
 
+/**
+ * Retrieve the list of lazy-native-modules names for the given bridge.
+ */
+- (NSDictionary<NSString *, Class> *)extraLazyModuleClassesForBridge:(RCTBridge *)bridge;
+
 @end

React/CxxBridge/RCTCxxBridge.mm

@@ -301,6 +301,7 @@ struct RCTInstanceCallback : public InstanceCallback {
   [self registerExtraModules];
   // Initialize all native modules that cannot be loaded lazily
   (void)[self _initializeModules:RCTGetModuleClasses() withDispatchGroup:prepareBridge lazilyDiscovered:NO];
+  [self registerExtraLazyModules];
 
   [_performanceLogger markStopForTag:RCTPLNativeModuleInit];
 
@@ -600,6 +601,57 @@ struct RCTInstanceCallback : public InstanceCallback {
   RCT_PROFILE_END_EVENT(RCTProfileTagAlways, @"");
 }
 
+- (void)registerExtraLazyModules
+{
+#if RCT_DEBUG
+  // This is debug-only and only when Chrome is attached, since it expects all modules to be already
+  // available on start up. Otherwise, we can let the lazy module discovery to load them on demand.
+  Class executorClass = [_parentBridge executorClass];
+  if (executorClass && [NSStringFromClass(executorClass) isEqualToString:@"RCTWebSocketExecutor"]) {
+    NSDictionary<NSString *, Class> *moduleClasses = nil;
+    if ([self.delegate respondsToSelector:@selector(extraLazyModuleClassesForBridge:)]) {
+      moduleClasses = [self.delegate extraLazyModuleClassesForBridge:_parentBridge];
+    }
+
+    if (!moduleClasses) {
+      return;
+    }
+
+    // This logic is mostly copied from `registerModulesForClasses:`, but with one difference:
+    // we must use the names provided by the delegate method here.
+    for (NSString *moduleName in moduleClasses) {
+      Class moduleClass = moduleClasses[moduleName];
+      if (RCTJSINativeModuleEnabled() && [moduleClass conformsToProtocol:@protocol(RCTJSINativeModule)]) {
+        continue;
+      }
+
+      // Check for module name collisions
+      RCTModuleData *moduleData = _moduleDataByName[moduleName];
+      if (moduleData) {
+        if (moduleData.hasInstance) {
+          // Existing module was preregistered, so it takes precedence
+          continue;
+        } else if ([moduleClass new] == nil) {
+          // The new module returned nil from init, so use the old module
+          continue;
+        } else if ([moduleData.moduleClass new] != nil) {
+          // Both modules were non-nil, so it's unclear which should take precedence
+          RCTLogError(@"Attempted to register RCTBridgeModule class %@ for the "
+                      "name '%@', but name was already registered by class %@",
+                      moduleClass, moduleName, moduleData.moduleClass);
+        }
+      }
+
+      moduleData = [[RCTModuleData alloc] initWithModuleClass:moduleClass bridge:self];
+
+      _moduleDataByName[moduleName] = moduleData;
+      [_moduleClassesByID addObject:moduleClass];
+      [_moduleDataByID addObject:moduleData];
+    }
+  }
+#endif
+}
+
 - (NSArray<RCTModuleData *> *)_initializeModules:(NSArray<id<RCTBridgeModule>> *)modules
                                withDispatchGroup:(dispatch_group_t)dispatchGroup
                                 lazilyDiscovered:(BOOL)lazilyDiscovered