Richard Eisenberg authored Jul 05, 2018 and Ben Gamari committed Jul 12, 2018

Read that note -- it's necessary to make sure that we can
always call typeKind without panicking. As discussed on #14873,
there were more checks and zonking to do, implemented here.
There are no known bugs fixed by this patch, but there are likely
unknown ones.

(cherry picked from commit cf67e59a)