Uncaught exceptions causes a silent exit

[Xenonym]

Tell us about your environment

• MarkBind Version: 1.16.1

What did you do? Please include the actual source code causing the issue.
If an exception is thrown that is not handled, MarkBind logs the exception but does not return anything to standard output. For example, suppose we have the following MarkBind source:

<!-- the following will cause an exception in Nunjucks -->
{% set error = " %}

What did you expect to happen?
MarkBind should print the exception to standard output / error, or at least indicate to the user that they should investigate the log file for more information.

What actually happened? Please include the actual, raw output.
markbind build aborts halfway with no feedback:

PS C:\Users\pzy5a\Desktop\testbind> markbind build
  __  __                  _      ____    _               _
 |  \/  |   __ _   _ __  | | __ | __ )  (_)  _ __     __| |
 | |\/| |  / _` | | '__| | |/ / |  _ \  | | | '_ \   / _` |
 | |  | | | (_| | | |    |   <  | |_) | | | | | | | | (_| |
 |_|  |_|  \__,_| |_|    |_|\_\ |____/  |_| |_| |_|  \__,_|

 v1.16.1
info: Website generation started at 18:13:12
info: Building assets...
info: Assets built
info: Generating pages...
[-] 0 / 1 pages built
PS C:\Users\pzy5a\Desktop\testbind>

However, the exception is logged:

2019-01-20T10:13:12.451Z - error: uncaughtException: (unknown path)
  expected block end in set statement date=Sun Jan 20 2019 18:13:12 GMT+0800 (Malay Peninsula Standard Time), pid=18160, uid=null, gid=null, cwd=C:\Users\pzy5a\Desktop\testbind, execPath=C:\Program Files\nodejs\node.exe, version=v8.15.0, argv=[C:\Program Files\nodejs\node.exe, C:\Program Files\nodejs\node_modules\markbind-cli\index.js, build], rss=63217664, heapTotal=60190720, heapUsed=26615736, external=836159, loadavg=[0, 0, 0], uptime=165999
Template render error: (unknown path)
  expected block end in set statement
    at Object.exports.prettifyError (C:\Users\pzy5a\Documents\GitHub\CS3281-2\markbind\node_modules\nunjucks\src\lib.js:34:15)
    at new_cls.render (C:\Users\pzy5a\Documents\GitHub\CS3281-2\markbind\node_modules\nunjucks\src\environment.js:472:27)
    at new_cls.renderString (C:\Users\pzy5a\Documents\GitHub\CS3281-2\markbind\node_modules\nunjucks\src\environment.js:328:21)
    at Object.module.exports.renderString (C:\Users\pzy5a\Documents\GitHub\CS3281-2\markbind\node_modules\nunjucks\index.js:80:14)
    at fs.readFile (C:\Users\pzy5a\Documents\GitHub\CS3281-2\markbind\src\lib\markbind\src\parser.js:416:36)
    at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:511:3)

[Xenonym]

Related to #265, but we should also solve the more general case of not surfacing anything when an uncaught exception is thrown.

[amad-person]

This behaviour is most likely because of a bug in Nunjucks. Errors were being swallowed on synchronous rendering. A fix was added by this PR in Nunjucks v3.1.7.

I installed Nunjucks 3.1.7 but markbind build still fails silently on adding a statement like {% set error = " %}.

I also tried configuring Nunjucks by adding nunjucks.configure({ throwOnUndefined: true }) in Site.js, Page.js and parser.js. This didn't throw an error too.

Apparently the errors were not being swallowed on asynchronous renders, so I tried adding callbacks in nunjucks.renderString() to handle errors (syntax) but I got the following:

(node:29797) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 logged listeners added. Use emitter.setMaxListeners() to increase limit
(node:29797) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 error listeners added. Use emitter.setMaxListeners() to increase limit

Does anyone know how to fix this?
Or has another approach to handle errors thrown by nunjucks?

[Xenonym]

@amad-person not sure if its a Nunjucks problem: the fact that the exception is logged means that Nunjucks is throwing the error (since otherwise the error can't be logged). I suspect it might be the logger (winston@2.4.4) that's swallowing the error after logging it?