Improve error stacks in development and debug mode

Author: Ruben Bridgewater

README.md

@@ -757,6 +757,35 @@ clients: 1, NodeJS: 6.2.0, Redis: 3.2.0, parser: javascript, connected by: tcp
 
 To get debug output run your `node_redis` application with `NODE_DEBUG=redis`.
 
+This is also going to result in good stack traces opposed to useless ones otherwise for any async operation.
+If you only want to have good stack traces but not the debug output run your application in development mode instead (`NODE_ENV=development`).
+
+Good stack traces are only activated in development and debug mode as this results in a significant performance penalty.
+
+___Comparison___:
+Useless stack trace:
+```
+ReplyError: ERR wrong number of arguments for 'set' command
+    at parseError (/home/ruben/repos/redis/node_modules/redis-parser/lib/parser.js:158:12)
+    at parseType (/home/ruben/repos/redis/node_modules/redis-parser/lib/parser.js:219:14)
+```
+Good stack trace:
+```
+ReplyError: ERR wrong number of arguments for 'set' command
+    at new Command (/home/ruben/repos/redis/lib/command.js:9:902)
+    at RedisClient.set (/home/ruben/repos/redis/lib/commands.js:9:3238)
+    at Context.<anonymous> (/home/ruben/repos/redis/test/good_stacks.spec.js:20:20)
+    at callFnAsync (/home/ruben/repos/redis/node_modules/mocha/lib/runnable.js:349:8)
+    at Test.Runnable.run (/home/ruben/repos/redis/node_modules/mocha/lib/runnable.js:301:7)
+    at Runner.runTest (/home/ruben/repos/redis/node_modules/mocha/lib/runner.js:422:10)
+    at /home/ruben/repos/redis/node_modules/mocha/lib/runner.js:528:12
+    at next (/home/ruben/repos/redis/node_modules/mocha/lib/runner.js:342:14)
+    at /home/ruben/repos/redis/node_modules/mocha/lib/runner.js:352:7
+    at next (/home/ruben/repos/redis/node_modules/mocha/lib/runner.js:284:14)
+    at Immediate._onImmediate (/home/ruben/repos/redis/node_modules/mocha/lib/runner.js:320:5)
+    at processImmediate [as _immediateCallback] (timers.js:383:17)
+```
+
 ## How to Contribute
 - Open a pull request or an issue about what you want to implement / change. We're glad for any help!
  - Please be aware that we'll only accept fully tested code.

changelog.md

@@ -11,6 +11,7 @@ Features
  -  The JS parser is from now on the new default as it is a lot faster than the hiredis parser
  -  This is no BC as there is no changed behavior for the user at all but just a performance improvement. Explicitly requireing the Hiredis parser is still possible.
 -  Added name property to all Redis functions (Node.js >= 4.0)
+-  Improved stack traces in development and debug mode
 
 Bugfixes
 

index.js

@@ -348,6 +348,9 @@ RedisClient.prototype.flush_and_error = function (error_attributes, options) {
         // Don't flush everything from the queue
         for (var command_obj = this[queue_names[i]].shift(); command_obj; command_obj = this[queue_names[i]].shift()) {
             var err = new errorClasses.AbortError(error_attributes);
+            if (command_obj.error) {
+                err.stack = err.stack + command_obj.error.stack.replace(/^Error.*?\n/, '\n');
+            }
             err.command = command_obj.command.toUpperCase();
             if (command_obj.args && command_obj.args.length) {
                 err.args = command_obj.args;
@@ -675,6 +678,9 @@ RedisClient.prototype.connection_gone = function (why, error) {
 
 RedisClient.prototype.return_error = function (err) {
     var command_obj = this.command_queue.shift();
+    if (command_obj.error) {
+        err.stack = command_obj.error.stack.replace(/^Error.*?\n/, 'ReplyError: ' + err.message + '\n');
+    }
     err.command = command_obj.command.toUpperCase();
     if (command_obj.args && command_obj.args.length) {
         err.args = command_obj.args;

lib/command.js

@@ -1,12 +1,17 @@
 'use strict';
 
+var debug_mode = require('../').debug_mode;
+var betterStackTraces = process.env.NODE_ENV && process.env.NODE_ENV.toUpperCase() === 'DEVELOPMENT' || debug_mode;
 
 function Command (command, args, callback, call_on_write) {
     this.command = command;
     this.args = args;
     this.buffer_args = false;
     this.callback = callback;
     this.call_on_write = call_on_write;
+    if (betterStackTraces) {
+        this.error = new Error();
+    }
 }
 
 module.exports = Command;