Panic on malformed newtype
The following causes a panic on GHC 9.6.1:
data A = A !B
newtype B = B C C
data C = C A
Result:
<no location info>: error:
panic! (the 'impossible' happened)
GHC version 9.6.1:
mkNewTyConRhs
B [C, C]
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/GHC/Utils/Panic.hs:189:37 in ghc:GHC.Utils.Panic
pprPanic, called at compiler/GHC/Tc/TyCl/Build.hs:70:27 in ghc:GHC.Tc.TyCl.Build
CallStack (from HasCallStack):
panic, called at compiler/GHC/Utils/Error.hs:454:29 in ghc:GHC.Utils.Error
GHC versions 9.4.5 and 9.2.5 do not panic and report the error correctly. I haven't tested other versions.
This is similar to #15523 (closed).