Stacktrace for syntax errors incorrectly points to the test file

[ecowden]

If I have a function under test with a syntax error like:

// demo.js
module.exports = function () { // missing closing brace

...and a test like:

// demoTest.js
const test = require('ava')
const demo = require('./demo')

test(async function (t) {
  t.ok(true)
})

Then the syntax error is reported pointing to the require statement in the test file instead of the file with the error:

Uncaught Exception:  /Users/cowdene/src/avaIssue/demoTest.js
  SyntaxError: Unexpected token )
    at Object.<anonymous> (/Users/cowdene/src/avaIssue/demoTest.js:2:14)

This is pretty confusing and is especially tricky for newer Node developers.

[novemberborn]

Either of these report the error:

// requireDemo.js
const demo = require('./demo')

// requireDemoFromString.js
var requireFromString = require('require-from-string');
requireFromString("const demo = require('./demo')", "hi.js")

However lib/babel uses process.on('uncaughtException') to catch the error, serialize it, and send it to the cli. Here's where the information gets lost.

I think Node runs this code when writing the error to stderr if a process crashes. This can somehow access the original source file and whatnot. Not sure how to get access that from JS.

[jamestalmage]

Related: nodejs/node-v0.x-archive#3452

[jamestalmage]

It's impossible to fix this in a clean way in JS, the V8 related issues are here:

https://code.google.com/p/v8/issues/detail?id=1914
https://code.google.com/p/v8/issues/detail?id=1281

The only workaround I can see is to wrap Module.prototype._compile to temporarily disable our uncaughtException handler. Here is a quick prototype of what I am thinking:

process.on('uncaughtException', function (e) {
  if (e.__thrownInsideModuleCompile__) {
    throw e;
  } else {
    console.log('error swallowed this will not work');
  }
});

var Module = module.constructor;

var oldCompile = Module.prototype._compile;

Module.prototype._compile = function (code, filename) {
  try {
    oldCompile.apply(this, arguments);
  } catch (e) {
    e.__thrownInsideModuleCompile__ = true;
    throw e;
  }
};

var requireFromString = require('require-from-string');

var badUserCode = 'function () {';

requireFromString(badUserCode, 'bar.js');

This means any errors thrown synchronously when a module is required are just going to crash the whole test. This will be true even inside tests:

import test from 'ava';

test('test A', t => t.pass());
test('test B', t => t.pass());
test('test C', t => require('./moduleThatThrowsSynchronously'));

This change would also make AVA a less than ideal place to test any code that attempts to wrap / manipulate Module._compile. (It would have given me headaches while developing capture-require for instance).

[jamestalmage]

sourcemap-support adds an unhandledException listener as well (disabling the helpful output). That can be fixed using the handleUncaughtExceptions option and setting it to false:

var sourceMapSupport = require('source-map-support');
sourceMapSupport.install({
    handleUncaughtExceptions: false,
        ...

not sure what additional problems that will cause.

[jamestalmage]

OK,
I think a much simpler solution would be to move this, down to here as well as setting the handleUncaughtExceptions flag I mentioned in the previous comment(set it here).

This is going to cause a few of our current api tests to fail.

I can work on this later tonight unless someone else wants to take it up. @sotojuan - You are already familiar with those tests. You wanna give it a go? You could start with jamestalmage@b198624 (or just emulate what I have done there). I think it might mean moving the syntax error test back to cli territory.

[sotojuan]

I'll give it a shot—probably later today or tomorrow.

[novemberborn]

👍 on the approach outlined by @jamestalmage. The main process will notice the test dying and log the error, and we get to use Node's error logging which includes the actual file.

[ecowden]

Just checked out the fix and it's giving the stack trace I'd expect. Thanks! 👍