3894: Match check enum record r=flodiebold a=JoshMcguigan
This PR implements match statement exhaustiveness checking for record type enums.
It also make a minor addition to the test infrastructure to allow testing against a single diagnostic, so you can be sure your test is triggering (or not) whichever diagnostic you expect.
Co-authored-by: Josh Mcguigan <joshmcg88@gmail.com>
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