Decouple Module System from Native Calls

Summary:
The JavaScript ecosystem doesn't have the notion of a built-in native module loader. Even Node is decoupled from its module loader. The module loader system is just JS that runs on top of the global `process` object which has all the built-in goodies.

Additionally there is no such thing as a global require. That is something unique to our providesModule system. In other module systems such as node, every require is contextual. Even registered npm names are localized by version.

The only global namespace that is accessible to the host environment is the global object. Normally module systems attaches itself onto the hooks provided by the host environment on the global object.

Currently, we have two forms of dispatch that reaches directly into the module system. executeJSCall which reaches directly into require. Everything now calls through the BatchedBridge module (except one RCTLog edge case that I will fix). I propose that the executors calls directly onto `BatchedBridge` through an instance on the global so that everything is guaranteed to go through it. It becomes the main communication hub.

I also propose that we drop the dynamic requires inside of MessageQueue/BatchBridge and instead have the modules register themselves with the bridge.

executeJSCall was originally modeled after the XHP equivalent. The XHP equivalent was designed that way because the act of doing the call was the thing that defined a dependency on the module from the page. However, that is not how React Native works.

The JS side is driving the dependencies by virtue of requiring new modules and frameworks and the existence of dependencies is driven by the JS side, so this design doesn't make as much sense.

The main driver for this is to be able to introduce a new module system like Prepack's module system. However, it also unlocks the possibility to do dead module elimination even in our current module system. It is currently not possible because we don't know which module might be called from native.

Since the module system now becomes decoupled we could publish all our providesModule modules as npm/CommonJS modules using a rewrite script. That's what React Core does.

That way people could use any CommonJS bundler such as Webpack, Closure Compiler, Rollup or some new innovation to create a JS bundle.

This diff expands the executeJSCalls to the BatchedBridge's three individual pieces to make them first class instead of being dynamic. This removes one layer of abstraction. Hopefully we can also remove more of the things that register themselves with the BatchedBridge (various EventEmitters) and instead have everything go through the public protocol. ReactMethod/RCT_EXPORT_METHOD.

public

Reviewed By: vjeux

Differential Revision: D2717535

fb-gh-sync-id: 70114f05483124f5ac5c4570422bb91a60a727f6

Examples/UIExplorer/UIExplorerUnitTests/RCTBridgeTests.m

@@ -54,10 +54,22 @@ RCT_EXPORT_MODULE()
   return YES;
 }
 
-- (void)executeJSCall:(__unused NSString *)name
-               method:(__unused NSString *)method
-            arguments:(__unused NSArray *)arguments
-             callback:(RCTJavaScriptCallback)onComplete
+- (void)flushedQueue:(RCTJavaScriptCallback)onComplete
+{
+  onComplete(nil, nil);
+}
+
+- (void)callFunctionOnModule:(NSString *)module
+                      method:(NSString *)method
+                   arguments:(NSArray *)args
+                    callback:(RCTJavaScriptCallback)onComplete
+{
+  onComplete(nil, nil);
+}
+
+- (void)invokeCallbackID:(NSNumber *)cbID
+               arguments:(NSArray *)args
+                callback:(RCTJavaScriptCallback)onComplete
 {
   onComplete(nil, nil);
 }

Examples/UIExplorer/UIExplorerUnitTests/RCTContextExecutorTests.m

@@ -123,8 +123,13 @@ static uint64_t _get_time_nanoseconds(void)
         } \
       } \
     }; \
+    var Bridge = { \
+      callFunctionReturnFlushedQueue: function(module, method, args) { \
+        modules[module].apply(modules[module], args); \
+      } \
+    }; \
     function require(module) { \
-      return modules[module]; \
+      return Bridge; \
     } \
   ";
 
@@ -138,12 +143,11 @@ static uint64_t _get_time_nanoseconds(void)
       for (int j = 0; j < runs; j++) {
         @autoreleasepool {
           double start = _get_time_nanoseconds();
-          [_executor executeJSCall:@"module"
-                           method:@"method"
-                        arguments:params
-                         callback:^(id json, __unused NSError *unused) {
-                           XCTAssert([json isEqual:@YES], @"Invalid return");
-                         }];
+          [_executor callFunctionOnModule:@"module"
+                                   method:@"method"
+                                arguments:params
+                                 callback:^(__unused id json, __unused NSError *unused) {
+                                 }];
           double run = _get_time_nanoseconds() - start;
           if ((j % frequency) == frequency - 1) { // Warmup
             total += run;