Allow developers to disable attributes injected by ngAria

[marcysutton]

One nice feature of ngAria is that developers can disable specific attributes that conflict with their own implementation, for example, if they already manage tabindex. Because of our mix of ngAria and custom accessibility support, opting out of attributes managed both by us and by ngAria is not possible. For example, see these two code snippets:

var app = angular.module( 'app', ['ngAnimate','ngMaterial'], 
  function config($ariaProvider) {
      $ariaProvider.config({
        tabindex: false,
        ariaInvalid: false
   });
});

<md-radio-group ng-model="data.group1">
    <md-radio-button value="Apple" aria-label="Apple">Apple</md-radio-button>
    <md-radio-button value="Banana" aria-label="Banana">Banana</md-radio-button>
    <md-radio-button value="Mango" aria-label="Mango">Mango</md-radio-button>
</md-radio-group>

tabindex is added to <md-radio-group> by Angular Material so only aria-invalid is suppressed, not tabindex. ngAria leaves the existing tabindex intact, as it should.

As much as it seems like a bad idea to allow people to disable accessibility support for attributes, should we create a mechanism to support custom disabling of attributes in this way, since it is supported by ngAria?

Example on Plunkr.

Related: #583 (bug)

[ThomasBurleson]

Can we not check the configuration of ngAria? Developers can use

$AriaProvider.config({ 'tabindex':false });

Then our $mdAria.expect( ) can get a reference to the configuration settings and internally check if that option is enabled.

var shouldCheckAriaAttribute =  $AriaProvider.$get().config;

[jarrodpayne]

@marcysutton good find. I'm experiencing this issue now. 👍 in hopes that it doesn't get pushed back further than 0.8.0.

[marcysutton]

@ThomasBurleson we don't actually expose the $ariaProvider in ngMaterial, we only pull in ngAria as a dependency (https://github.com/angular/material/blob/master/scripts/gulp-utils.js#L151). It's an unusual setup, so I can't quite figure out how to expose it. I'd love your input.

https://docs.angularjs.org/api/ngAria/provider/$ariaProvider