inspect should skip properties that begin with $

Opal (Ruby to JavaScript transpiler) adds special properties to all objects which introduce a circular graph. For example:

require('opal-runtime')

const a = []
console.log(a['$class']['$class']['$class']['$class']['$class']['$class'])

When inspect encounters one of these objects, it enters an infinite recursion and hangs.

inspect should skip properties on an object that begin with $. If not the default, it should provide a configuration switch to activate this filtering.

You could debate that Opal should not be adding properties that are accessible via (for name in obj). The problem is, the Opal creators don’t agree, and that leaves us all that use it with test suites that hang on failures.

Here’s the proposed change to getEnumerableProperties.js.

module.exports = function getEnumerableProperties(object) {
  var result = [];
  for (var name in object) {
    if (!name.startsWith('$')) result.push(name);
  }
  return result;
};

[mojavelinux]

That’s fine. In fact, the discussion prompted a change in Opal itself. Opal is now going to define properties using the defineProperty mechanism (with enumerable set to false), which will exclude them from being picked up by for…in. See https://github.com/opal/opal/commit/34f89df1d700be5143b9dbcc9886202fd2bfd3ca

[keithamus]

chai should not hang the node process and eat up 100% of the CPU

Yep. Absolutely. There’s two problems here. Firstly the inspection engine hangs. This will be fixed in the next few months as we introduce loupe as a new inspection engine, which fixes circular refs. The next problem is why the inspection engine is ever run for passing tests. This is addressed in #585 which is a much longer architectural change.

I’m saying let’s deal with a problem we have this ecosystem that’s real.

This is a valid concern, but Opal is one library out of N. Making concessions for individual libraries is not something we’re interested in doing, as its a slippery slope. We could also block the $$typeof$$ magic strings that some libraries like React have, but its not an interest we have. Again though, the new inspection engine will enable plugins to interface with these paths to allow for this kind of behavior.

TL;DR. Sorry, it sucks that this is the case right now. We’re working hard to fix it. Rest assured it will be fixed - just not in the exact way that Opal declares it’s circular properties.