Fix Connect to Metro after Reload in Bridgeless mode

Summary:
We received [this issue](facebook#43764) from OSS where an app can't connect to Metro on reloads in the following scenario:

* Start the App when metro does not run.
* Observe the error screen
* Start Metro
* Press Reload
* Observe the error message again

While the desired behavior should be to connect to Metro now that this is running.

The root cause of the problem is that the RCTHost is initialized with a value of the `bundleURL` that is `nil`. Upon reload, the RCTHost is **not** recreated: the instance is restarted, but with the previous `bundleURL`, which is still `nil`.

The solution is to initialize the `RCTHost` with a closure that re-evaluate the `bundleURL` whenever it is invoked and to evaluate it only on `start`, to keep the initialization path light.
This way, when the app is started with Metro not running, the `bundleURL` is `nil`. But when it is reloaded with Metro starting, the `bundleURL` is properly initialized.

Note that the changes in this diff are not breaking as I reimplemented (and deprecated) the old initializer so that they should work in the same way.

## Changelog:
[iOS][Fixed] - Let RCTHost be initialized with a function to provide the `bundleURL` so that it can connect to metro on Reload when the url changes.

Differential Revision: D55916135

packages/react-native/Libraries/AppDelegate/RCTAppDelegate.mm

@@ -248,13 +248,18 @@ - (Class)getModuleClassFromName:(const char *)name
 
 - (RCTRootViewFactory *)createRCTRootViewFactory
 {
+  __weak __typeof(self) weakSelf = self;
+  RCTBundleURLBlock bundleUrlBlock = ^{
+    RCTAppDelegate *strongSelf = weakSelf;
+    return strongSelf.bundleURL;
+  };
+
   RCTRootViewFactoryConfiguration *configuration =
-      [[RCTRootViewFactoryConfiguration alloc] initWithBundleURL:self.bundleURL
-                                                  newArchEnabled:self.fabricEnabled
-                                              turboModuleEnabled:self.turboModuleEnabled
-                                               bridgelessEnabled:self.bridgelessEnabled];
+      [[RCTRootViewFactoryConfiguration alloc] initWithBundleURLBlock:bundleUrlBlock
+                                                       newArchEnabled:self.fabricEnabled
+                                                   turboModuleEnabled:self.turboModuleEnabled
+                                                    bridgelessEnabled:self.bridgelessEnabled];
 
-  __weak __typeof(self) weakSelf = self;
   configuration.createRootViewWithBridge = ^UIView *(RCTBridge *bridge, NSString *moduleName, NSDictionary *initProps)
   {
     return [weakSelf createRootViewWithBridge:bridge moduleName:moduleName initProps:initProps];

packages/react-native/Libraries/AppDelegate/RCTRootViewFactory.h

@@ -24,6 +24,7 @@ typedef UIView *_Nonnull (
 typedef RCTBridge *_Nonnull (
     ^RCTCreateBridgeWithDelegateBlock)(id<RCTBridgeDelegate> delegate, NSDictionary *launchOptions);
 typedef NSURL *_Nullable (^RCTSourceURLForBridgeBlock)(RCTBridge *bridge);
+typedef NSURL *_Nullable (^RCTBundleURLBlock)();
 typedef NSArray<id<RCTBridgeModule>> *_Nonnull (^RCTExtraModulesForBridgeBlock)(RCTBridge *bridge);
 typedef NSDictionary<NSString *, Class> *_Nonnull (^RCTExtraLazyModuleClassesForBridge)(RCTBridge *bridge);
 typedef BOOL (^RCTBridgeDidNotFindModuleBlock)(RCTBridge *bridge, NSString *moduleName);
@@ -41,7 +42,7 @@ typedef BOOL (^RCTBridgeDidNotFindModuleBlock)(RCTBridge *bridge, NSString *modu
 @property (nonatomic, assign, readonly) BOOL turboModuleEnabled;
 
 /// Return the bundle URL for the main bundle.
-@property (nonatomic) NSURL *bundleURL;
+@property (nonatomic, nonnull) RCTBundleURLBlock bundleURLBlock;
 
 /**
  * Use this method to initialize a new instance of `RCTRootViewFactoryConfiguration` by passing a `bundleURL`
@@ -52,10 +53,15 @@ typedef BOOL (^RCTBridgeDidNotFindModuleBlock)(RCTBridge *bridge, NSString *modu
  * pointing to a path inside the app resources, e.g. `file://.../main.jsbundle`.
  *
  */
+- (instancetype)initWithBundleURLBlock:(RCTBundleURLBlock)bundleURLBlock
+                        newArchEnabled:(BOOL)newArchEnabled
+                    turboModuleEnabled:(BOOL)turboModuleEnabled
+                     bridgelessEnabled:(BOOL)bridgelessEnabled NS_DESIGNATED_INITIALIZER;
+
 - (instancetype)initWithBundleURL:(NSURL *)bundleURL
                    newArchEnabled:(BOOL)newArchEnabled
                turboModuleEnabled:(BOOL)turboModuleEnabled
-                bridgelessEnabled:(BOOL)bridgelessEnabled;
+                bridgelessEnabled:(BOOL)bridgelessEnabled __deprecated;
 
 /**
  * Block that allows to override logic of creating root view instance.

packages/react-native/Libraries/AppDelegate/RCTRootViewFactory.mm

@@ -57,9 +57,23 @@ - (instancetype)initWithBundleURL:(NSURL *)bundleURL
                    newArchEnabled:(BOOL)newArchEnabled
                turboModuleEnabled:(BOOL)turboModuleEnabled
                 bridgelessEnabled:(BOOL)bridgelessEnabled
+{
+  return [self
+      initWithBundleURLBlock:^{
+        return bundleURL;
+      }
+              newArchEnabled:newArchEnabled
+          turboModuleEnabled:turboModuleEnabled
+           bridgelessEnabled:bridgelessEnabled];
+}
+
+- (instancetype)initWithBundleURLBlock:(RCTBundleURLBlock)bundleURLBlock
+                        newArchEnabled:(BOOL)newArchEnabled
+                    turboModuleEnabled:(BOOL)turboModuleEnabled
+                     bridgelessEnabled:(BOOL)bridgelessEnabled
 {
   if (self = [super init]) {
-    _bundleURL = bundleURL;
+    _bundleURLBlock = bundleURLBlock;
     _fabricEnabled = newArchEnabled;
     _turboModuleEnabled = turboModuleEnabled;
     _bridgelessEnabled = bridgelessEnabled;
@@ -214,13 +228,13 @@ - (void)createReactHostIfNeeded:(NSDictionary *)launchOptions
   }
 
   __weak __typeof(self) weakSelf = self;
-  _reactHost = [[RCTHost alloc] initWithBundleURL:[self bundleURL]
-                                     hostDelegate:nil
-                       turboModuleManagerDelegate:_turboModuleManagerDelegate
-                                 jsEngineProvider:^std::shared_ptr<facebook::react::JSRuntimeFactory>() {
-                                   return [weakSelf createJSRuntimeFactory];
-                                 }
-                                    launchOptions:launchOptions];
+  _reactHost = [[RCTHost alloc] initWithBundleURLProvider:self->_configuration.bundleURLBlock
+                                             hostDelegate:nil
+                               turboModuleManagerDelegate:_turboModuleManagerDelegate
+                                         jsEngineProvider:^std::shared_ptr<facebook::react::JSRuntimeFactory>() {
+                                           return [weakSelf createJSRuntimeFactory];
+                                         }
+                                            launchOptions:launchOptions];
   [_reactHost setBundleURLProvider:^NSURL *() {
     return [weakSelf bundleURL];
   }];
@@ -276,7 +290,7 @@ - (BOOL)bridge:(RCTBridge *)bridge didNotFindModule:(NSString *)moduleName
 
 - (NSURL *)bundleURL
 {
-  return self->_configuration.bundleURL;
+  return self->_configuration.bundleURLBlock();
 }
 
 @end

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTHost+Internal.h

@@ -9,8 +9,6 @@
 
 #import "RCTContextContainerHandling.h"
 
-typedef NSURL * (^RCTHostBundleURLProvider)(void);
-
 @interface RCTHost (Internal)
 
 - (void)registerSegmentWithId:(NSNumber *)segmentId path:(NSString *)path;

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTHost.h

@@ -21,6 +21,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 @protocol RCTTurboModuleManagerDelegate;
 
+typedef NSURL *_Nullable (^RCTHostBundleURLProvider)(void);
+
 // Runtime API
 
 @protocol RCTHostDelegate <NSObject>
@@ -45,11 +47,17 @@ typedef std::shared_ptr<facebook::react::JSRuntimeFactory> (^RCTHostJSEngineProv
 
 @interface RCTHost : NSObject
 
+- (instancetype)initWithBundleURLProvider:(RCTHostBundleURLProvider)provider
+                             hostDelegate:(id<RCTHostDelegate>)hostDelegate
+               turboModuleManagerDelegate:(id<RCTTurboModuleManagerDelegate>)turboModuleManagerDelegate
+                         jsEngineProvider:(RCTHostJSEngineProvider)jsEngineProvider
+                            launchOptions:(nullable NSDictionary *)launchOptions NS_DESIGNATED_INITIALIZER;
+
 - (instancetype)initWithBundleURL:(NSURL *)bundleURL
                      hostDelegate:(id<RCTHostDelegate>)hostDelegate
        turboModuleManagerDelegate:(id<RCTTurboModuleManagerDelegate>)turboModuleManagerDelegate
                  jsEngineProvider:(RCTHostJSEngineProvider)jsEngineProvider
-                    launchOptions:(nullable NSDictionary *)launchOptions NS_DESIGNATED_INITIALIZER;
+                    launchOptions:(nullable NSDictionary *)launchOptions __deprecated;
 
 @property (nonatomic, weak, nullable) id<RCTHostRuntimeDelegate> runtimeDelegate;
 

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTHost.mm

@@ -79,15 +79,31 @@ + (void)initialize
   _RCTInitializeJSThreadConstantInternal();
 }
 
-/**
- Host initialization should not be resource intensive. A host may be created before any intention of using React Native
- has been expressed.
- */
 - (instancetype)initWithBundleURL:(NSURL *)bundleURL
                      hostDelegate:(id<RCTHostDelegate>)hostDelegate
        turboModuleManagerDelegate:(id<RCTTurboModuleManagerDelegate>)turboModuleManagerDelegate
                  jsEngineProvider:(RCTHostJSEngineProvider)jsEngineProvider
                     launchOptions:(nullable NSDictionary *)launchOptions
+{
+  return [self
+       initWithBundleURLProvider:^{
+         return bundleURL;
+       }
+                    hostDelegate:hostDelegate
+      turboModuleManagerDelegate:turboModuleManagerDelegate
+                jsEngineProvider:jsEngineProvider
+                   launchOptions:launchOptions];
+}
+
+/**
+ Host initialization should not be resource intensive. A host may be created before any intention of using React Native
+ has been expressed.
+ */
+- (instancetype)initWithBundleURLProvider:(RCTHostBundleURLProvider)provider
+                             hostDelegate:(id<RCTHostDelegate>)hostDelegate
+               turboModuleManagerDelegate:(id<RCTTurboModuleManagerDelegate>)turboModuleManagerDelegate
+                         jsEngineProvider:(RCTHostJSEngineProvider)jsEngineProvider
+                            launchOptions:(nullable NSDictionary *)launchOptions
 {
   if (self = [super init]) {
     _hostDelegate = hostDelegate;
@@ -99,7 +115,6 @@ - (instancetype)initWithBundleURL:(NSURL *)bundleURL
     _launchOptions = [launchOptions copy];
 
     __weak RCTHost *weakSelf = self;
-
     auto bundleURLGetter = ^NSURL *()
     {
       RCTHost *strongSelf = weakSelf;
@@ -124,7 +139,6 @@ - (instancetype)initWithBundleURL:(NSURL *)bundleURL
       return strongSelf->_bundleURLProvider();
     };
 
-    [self _setBundleURL:bundleURL];
     [_bundleManager setBridgelessBundleURLGetter:bundleURLGetter
                                        andSetter:bundleURLSetter
                                 andDefaultGetter:defaultBundleURLGetter];
@@ -170,6 +184,7 @@ - (instancetype)initWithBundleURL:(NSURL *)bundleURL
 
 - (void)start
 {
+  [self _setBundleURL:_bundleURLProvider()];
   auto &inspectorFlags = jsinspector_modern::InspectorFlags::getInstance();
   if (inspectorFlags.getEnableModernCDPRegistry() && !_inspectorPageId.has_value()) {
     _inspectorTarget =