[Bridge] Consistently post "DidFailToLoad" notification when there's an error

Summary:
Previously the bridge sometimes never fired RCTJavaScriptDidLoadNotification or RCTJavaScriptDidFailToLoadNotification if there was an error (for example, if the source code loaded but we couldn't inject the JSON config). This diff moves the error handling into a method called `stopLoadingWithError` that the bridge can call whenever there is an error.

Also if the script failed to load, the BatchedBridge still called `executeSourceCode`. With this diff the `_loading` flag is set to NO when the script fails to load, and `executeSourceCode` returns immediately when `_loading` is false. This way the bridge does not try to execute JS when there is a loading error.
Closes https://github.com/facebook/react-native/pull/2520
Github Author: James Ide <ide@jameside.com>

React/Base/RCTBatchedBridge.m

@@ -117,8 +117,15 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
 
   dispatch_group_t initModulesAndLoadSource = dispatch_group_create();
   dispatch_group_enter(initModulesAndLoadSource);
+  __weak RCTBatchedBridge *weakSelf = self;
   __block NSString *sourceCode;
-  [self loadSource:^(__unused NSError *error, NSString *source) {
+  [self loadSource:^(NSError *error, NSString *source) {
+    if (error) {
+      dispatch_async(dispatch_get_main_queue(), ^{
+        [weakSelf stopLoadingWithError:error];
+      });
+    }
+    
     sourceCode = source;
     dispatch_group_leave(initModulesAndLoadSource);
   }];
@@ -131,7 +138,6 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
     RCTProfileHookModules(self);
   }
 
-  __weak RCTBatchedBridge *weakSelf = self;
   __block NSString *config;
   dispatch_group_enter(initModulesAndLoadSource);
   dispatch_async(bridgeQueue, ^{
@@ -150,16 +156,24 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
       // We're not waiting for this complete to leave the dispatch group, since
       // injectJSONConfiguration and executeSourceCode will schedule operations on the
       // same queue anyway.
-      [weakSelf injectJSONConfiguration:config onComplete:^(__unused NSError *error) {
+      [weakSelf injectJSONConfiguration:config onComplete:^(NSError *error) {
         RCTPerformanceLoggerEnd(RCTPLNativeModuleInit);
+        if (error) {
+          dispatch_async(dispatch_get_main_queue(), ^{
+            [weakSelf stopLoadingWithError:error];
+          });
+        }
       }];
       dispatch_group_leave(initModulesAndLoadSource);
     });
   });
 
-  dispatch_group_notify(initModulesAndLoadSource, bridgeQueue, ^{
+  dispatch_group_notify(initModulesAndLoadSource, dispatch_get_main_queue(), ^{
-    if (sourceCode) {
+    RCTBatchedBridge *strongSelf = weakSelf;
-      [weakSelf executeSourceCode:sourceCode];
+    if (sourceCode && strongSelf.loading) {
+      dispatch_async(bridgeQueue, ^{
+        [weakSelf executeSourceCode:sourceCode];
+      });
     }
   });
 }
@@ -172,23 +186,6 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
   RCTSourceLoadBlock onSourceLoad = ^(NSError *error, NSString *source) {
     RCTProfileEndAsyncEvent(0, @"init,download", cookie, @"JavaScript download", nil);
     RCTPerformanceLoggerEnd(RCTPLScriptDownload);
-
-    if (error) {
-      NSArray *stack = error.userInfo[@"stack"];
-      if (stack) {
-        [self.redBox showErrorMessage:error.localizedDescription
-                            withStack:stack];
-      } else {
-        [self.redBox showErrorMessage:error.localizedDescription
-                          withDetails:error.localizedFailureReason];
-      }
-
-      NSDictionary *userInfo = @{@"bridge": self, @"error": error};
-      [[NSNotificationCenter defaultCenter] postNotificationName:RCTJavaScriptDidFailToLoadNotification
-                                                          object:_parentBridge
-                                                        userInfo:userInfo];
-    }
-
     _onSourceLoad(error, source);
   };
 
@@ -283,7 +280,6 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
                                                       object:self];
 }
 
-
 - (void)setupExecutor
 {
   [_javaScriptExecutor setUp];
@@ -313,12 +309,7 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
 
   [_javaScriptExecutor injectJSONText:configJSON
                   asGlobalObjectNamed:@"__fbBatchedBridgeConfig"
-                             callback:^(NSError *error) {
+                             callback:onComplete];
-    if (error) {
-      [self.redBox showError:error];
-    }
-    onComplete(error);
-  }];
 }
 
 - (void)executeSourceCode:(NSString *)sourceCode
@@ -333,7 +324,9 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
 
   [self enqueueApplicationScript:sourceCode url:self.bundleURL onComplete:^(NSError *loadError) {
     if (loadError) {
-      [self.redBox showError:loadError];
+      dispatch_async(dispatch_get_main_queue(), ^{
+        [self stopLoadingWithError:loadError];
+      });
       return;
     }
 
@@ -352,6 +345,28 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
   }];
 }
 
+- (void)stopLoadingWithError:(NSError *)error
+{
+  RCTAssertMainThread();
+  
+  if (!self.isValid || !self.loading) {
+    return;
+  }
+  
+  _loading = NO;
+  
+  NSArray *stack = error.userInfo[@"stack"];
+  if (stack) {
+    [self.redBox showErrorMessage:error.localizedDescription withStack:stack];
+  } else {
+    [self.redBox showError:error];
+  }
+  
+  NSDictionary *userInfo = @{@"bridge": self, @"error": error};
+  [[NSNotificationCenter defaultCenter] postNotificationName:RCTJavaScriptDidFailToLoadNotification
+                                                      object:_parentBridge
+                                                    userInfo:userInfo];
+}
 
 RCT_NOT_IMPLEMENTED(- (instancetype)initWithBundleURL:(__unused NSURL *)bundleURL
                     moduleProvider:(__unused RCTBridgeModuleProviderBlock)block