Support a maximum depth to protect against malicious payloads

[kddnewton]

Bison supports YYMAXDEPTH (docs), we should do something similar so that we can provide a better experience than a SystemStackError or equivalent.

[HeyNonster]

The depth in Bison defaults to 10000 but in #3083 Prism's default depth was set to 1000. parse.y has a much higher limit and we were curious if the discrepancy was an intentional choice.

cc: @bquorning

[kddnewton]

Whoops, that's just a mistake. I misread the number of 0s in the bison docs. Feel like a contribution? We need to update defines.h.

Out of curiosity did you actually hit this depth? (I'm hoping I didn't break your app.)

[bquorning]

We actually did hit this limit, when rendering some view templates in Rails. 😅

We'll look into fixing defines.h tomorrow.

[kddnewton]

Ahh dang sorry about that! If you don't have the time tomorrow no worries I can do it. But I'll give you a day to get a contribution in :)

[bquorning]

Eh, nothing that a rollback couldn’t fix. Don’t worry about it.

PR ready at #3413.

[HeyNonster]

Agreed, it wasn't much of a hassle. Thank you for all your great work on Prism!

[kddnewton]

Nice. I will ask the branch maintainer for 3.4 to backport this so that it goes out in the next patch release (hopefully).