Mentoring for implementing #8004

[David Luposchainsky]

Hey Devs,

I haven't worked on GHC before, so I'm having trouble finding an entry
point to implementing the AMP warnings (#8004). I only have a rough
working knowledge of GHC's inner workings, but it would be a shame if
the ticket wasn't resolved until the 7.8 deadline (which is somewhere in
September if I remember it right).
My last approach was grepping through the source for "DEPRECATED" and
seeing whether there would be an appropriate place for these warnings
there, but that wasn't very fruitful.

Long story short: can anyone point me in the right direction? I assume
the right place to look is somewhere in the typechecker where there's a
type class environment, and that's as far as I've come. (It's hard to
understand thousands of lines when you're not even sure you're in the
right place ...)

Greetings,
David