typeahead: Properly handle custom triggers.

[aero31aero]

We have a kind of elusive bug in our custom typeahead triggers that is applicable only for characters that require two keypresses to type and is only exhibited usually when you're typing fast enough.

It just so happens that the only custom trigger we currently use is > for triggering the stream-topic typeahead, and pressing it is a combination of two keys: Shift + ..

Here's how the current code looks:

keyup: (e) {
  if (trigger_selection(e)) {
    select();
  }
}

Now, inside the trigger selection function, if we ask for e.keyCode, we always get 190 which is the keycode for .. Thus, we need to use e.key which gives us the intended value >... unless, the person release the shift key first and then releases the . key. Both these keyup events fail the check because we get e.key = '' and e.key = '.' respectively.

To fix this reliably while preserving the similar behavior (of taking action on keyup), here's a proposed solution:

let result = false;

keypress: (e) {
  if (trigger_selection(e)) {
    result = true;
  }
}

keyup: (e) {
  if (result) {
    result = false;
    select();
  }
}