perf(ngOptions): only perform deep equality check on ngModel if using track by

[booleanbetrayal]

Closes #11447

[booleanbetrayal]

Wish I had a better understanding of unknownValue usage in select + options. Had to revert the spec back to its form in ef894c8.

[petebacondarwin]

OK, so the reason for this is that, if the model is null then element.val() is empty but if the model contains a value that doesn't match any option then element.val() is '?'.

When we remove the option the value becomes invalid so we get '?' but then the model is cleared out and becomes null. If we have a watch on the model then this will cause the ngModel to run $render, which update the element value to ''.

I think that what we need is to trigger a new call to $render when the selected option is removed...

[petebacondarwin]

Actually what we need to do is fix the bit of code inside updateOptions (https://github.com/angular/angular.js/pull/11448/files#diff-0a9e86a58b2663074f51454f7a18a0efR646) that checks if the model has changed

[petebacondarwin]

I'll take a better look over the weekend but I think this is good.

[booleanbetrayal]

👍

[gkalpak]

I might add deep (equality) or something, to make it more clear.
(Technically, even in the default case, it is checking for equality (by reference).)

[booleanbetrayal]

good point! updated in rebased commit below.

[Narretz]

There's a also regression with circular references in models which was introduced by 6a03ca2 here: #11372

[barillax]

👍

[nbrustein]

👍

[petebacondarwin]

Thanks @booleanbetrayal for this

[booleanbetrayal]

np ... thanks @petebacondarwin !