add a callstack to errors in browser and msg (#1369)

js/msg.js

@@ -78,12 +78,12 @@
 
     send(data, target = 'extension') {
       return browser.runtime.sendMessage({data, target})
-        .then(unwrapResponse);
+        .then(unwrapResponseFactory('send'));
     },
 
     sendTab(tabId, data, options, target = 'tab') {
       return browser.tabs.sendMessage(tabId, {data, target}, options)
-        .then(unwrapResponse);
+        .then(unwrapResponseFactory('sendTab'));
     },
 
     _execute(types, ...args) {
@@ -138,9 +138,16 @@
     };
   }
 
-  function unwrapResponse({data, error} = {error: {message: ERR_NO_RECEIVER}}) {
+  function unwrapResponseFactory(name) {
+    // Saving the local callstack before making an async call
+    return unwrapResponse.bind(null, new Error(`Callstack before invoking msg.${name}:`));
+  }
+
+  function unwrapResponse(localErr, {data, error} = {error: {message: ERR_NO_RECEIVER}}) {
     return error
-      ? Promise.reject(Object.assign(new Error(error.message), error))
+      ? Promise.reject(Object.assign(localErr, error, error.stack && {
+        stack: `${error.stack}\n${localErr.stack}`,
+      }))
       : data;
   }
 

js/polyfill.js

@@ -23,14 +23,21 @@
     };
     const promisify = function (fn, ...args) {
       let res;
-      try {
       let resolve, reject;
+      // Saving the local callstack before making an async call
+      const err = new Error();
+      try {
+        args.push((...results) => {
+          const {lastError} = chrome.runtime;
+          if (lastError) {
+            err.message = lastError.message;
+            reject(err);
+          } else {
             /* Some callbacks have 2 parameters so we're resolving as an array in that case.
                For example, chrome.runtime.requestUpdateCheck and chrome.webRequest.onAuthRequired */
-        args.push((...results) =>
-          chrome.runtime.lastError ?
-            reject(new Error(chrome.runtime.lastError.message)) :
-            resolve(results.length <= 1 ? results[0] : results));
+            resolve(results.length <= 1 ? results[0] : results);
+          }
+        });
         fn.apply(this, args);
         res = new Promise((...rr) => ([resolve, reject] = rr));
       } catch (err) {