Define getters run twice. setVal is missing on first run.

[marshallswain]

With the latest version of Can, all of my define getters are getting run twice. On the first run, setVal is absent. On the second, it is present.

See this JSBin

can.Component.extend({
  tag: "home-page",
  template: can.view('home-template'),
  viewModel: {
    define: {
      names: {
        get(val, setVal){

          console.log('ARGUMENT COUNT:' + arguments.length);

          // This check is now necessary
          if (setVal) {
            console.log('There you are, setVal!');
            return val;
          }

          console.log('no setVal');
          return [];
        }
      }
    }
  }
});

[daffl]

Is that bound to a select field?

[marshallswain]

Not in the JSBin: http://jsbin.com/ruvako/edit?html,js,console,output

It's simply

{{names}}

[dylanrtt]

Here is a simpler example:
http://jsbin.com/qayicihipa/edit?html,js,console,output

It doesn't seem to happen when you bind directly to the map before the stache binding.

The same behavior occurs if you try to read the property before binding it.

[justinbmeyer]

This is due to the return readButDontObserveCompute(computedAttr.compute); added in #1915.

[justinbmeyer]

Instead of the solution for #1915, we should probably observe on the compute and not on the property itself. Basically flip the behavior around. Perhaps __get should check if it's a computed property and not call can.__observe around here: https://github.com/canjs/canjs/blob/minor/map/map.js#L246

[justinbmeyer]

A more simple test would probably have something like:

c = can.compute(function(){
  return m.attr("p");
})

Where p is a async defined property on map m.

[daffl]

Caused by #2224