[a11y] Disabled dates aren't actually disabled in markup

[backwardok]

When a date is disabled, CSS is applied to make it look disabled (CalendarDay--blocked-calendar, CalendarDay--blocked-out-of-range):

However, this date is still clickable with a mouse (even if the mouse click doesn't do anything in the UI), can be navigated to with a keyboard (you can arrow through disabled dates), and doesn't indicate that those dates are disabled to a screen reader user (because the button itself is not actually disabled).

Example where you can see this: http://airbnb.io/react-dates/?selectedKind=DRP%20-%20Day%20Props&selectedStory=blocks%20fridays&full=0&down=1&left=1&panelRight=0&downPanel=storybook%2Factions%2Factions-panel

[backwardok]

@majapw can you think of a reason why someone would not want to have the disabled attribute on the button underlying the date?

Note: this likely means messing with how next/previous day handling works for months (and what does this mean if you open a month in the past where the past is disabled? Or should you just not be allowed to do that either?

[majapw]

I think a couple of things are being conflated here.

1. I am surprised that the VO does not read out that the date is unavailable. That's like specifically what https://github.com/airbnb/react-dates/blob/master/src/components/CalendarDay.jsx#L113 is for. So that is a bug.

2. We can definitely disable the button for a disabled date. That was just an oversight on my part.

this likely means messing with how next/previous day handling works for months

3. I don't understand why these things would be related. We have talked about possibly disabling month navigation when it would take you to exclusively blocked dates (Limited months range navigation (add min / max date props) #339 and I think there's another issue as well), but that seems a separate discussion from disabling the blocked buttons?

[erin-doyle]

So I've submitted a PR to address the unavailable dates not being read as such by screen readers.

I did also locally code the disabling of the buttons for the unavailable dates. However, upon testing, it occurred to me that if the buttons are disabled then those users depending on screen readers would be blocked from being able to navigate over those dates and nothing would read to them why they were being blocked from moving back or forward any further. It works great for sighted people but I wonder if it would be a confusing user experience for those that are not.

[majapw]

@erin-doyle Yeah this was a concern of mine as well. I think we should maybe think more deeply on whether or not to disable blocked buttons for this reason.