Pattern synonym name is mangled when patterns are non-exhaustive
pattern A n <- ... where
A 0 = ...
When a pattern synonym is non-exhaustive its name is mangled:
>>> A 3
"*** Exception: /tmp/tmp.t0h0pMgwWb.hs:(4,1)-(5,14): Non-exhaustive patterns in function $bA
“Non-exhaustive patterns in pattern synonym A”
Comment from ticket #11367 (closed).