Send early logs to Metro too

Summary:
If you `console.log` early enough in the initialization sequence, it won't get sent to Metro because `hmrClient` isn't initialized yet. I've added a rolling array to catch at most 100 of those, and send them after we initialize.

Changelog: [General] [Fixed] - Early logs don't get dropped by Metro now

Reviewed By: cpojer

Differential Revision: D17952097

fbshipit-source-id: 964b4735a6a7c3ccd115f44151139d718bf5b26d

Libraries/Utilities/HMRClient.js

@@ -23,6 +23,7 @@ let hmrClient = null;
 let hmrUnavailableReason: string | null = null;
 let currentCompileErrorMessage: string | null = null;
 let didConnect: boolean = false;
+let pendingLogs: Array<[LogLevel, Array<mixed>]> = [];
 
 type LogLevel =
   | 'trace'
@@ -101,8 +102,16 @@ const HMRClient: HMRClientNativeInterface = {
   },
 
   log(level: LogLevel, data: Array<mixed>) {
+    if (!hmrClient) {
+      // Catch a reasonable number of early logs
+      // in case hmrClient gets initialized later.
+      pendingLogs.push([level, data]);
+      if (pendingLogs.length > 100) {
+        pendingLogs.shift();
+      }
+      return;
+    }
     try {
-      if (hmrClient) {
       let message;
       if (global.Symbol) {
         message = JSON.stringify({
@@ -133,7 +142,6 @@ const HMRClient: HMRClientNativeInterface = {
       }
 
       hmrClient.send(message);
-      }
     } catch (error) {
       // If sending logs causes any failures we want to silently ignore them
       // to ensure we do not cause infinite-logging loops.
@@ -244,6 +252,7 @@ Error: ${e.message}`;
     }
 
     registerBundleEntryPoints(hmrClient);
+    flushEarlyLogs(hmrClient);
   },
 };
 
@@ -276,6 +285,16 @@ function registerBundleEntryPoints(client) {
   }
 }
 
+function flushEarlyLogs(client) {
+  try {
+    pendingLogs.forEach(([level: LogLevel, data: Array<mixed>]) => {
+      HMRClient.log(level, data);
+    });
+  } finally {
+    pendingLogs.length = 0;
+  }
+}
+
 function dismissRedbox() {
   if (
     Platform.OS === 'ios' &&