Panic in pprMatch when "deriving Foldable" is used with -ddump-tc-trace
Summary
Trying to compile the following program in current HEAD with -ddump-tc-trace
flag results in a panic:
{-# LANGUAGE DeriveFoldable #-}
module Test where
data T a = MkT a
deriving Foldable
rndghc: panic! (the 'impossible' happened)
GHC version 9.3.20211004:
pprMatch
CaseAlt
[f, (MkT a1)]
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/GHC/Utils/Panic.hs:181:37 in ghc:GHC.Utils.Panic
pprPanic, called at compiler/GHC/Hs/Expr.hs:1364:29 in ghc:GHC.Hs.Expr
Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug
I know that this issue is already present in 6141aef4, but I didn't check any further. 8.10.7 doesn't have this issue as far as I'm aware.
Steps to reproduce
Run ghc -ddump-tc-trace Test.hs
on the program above.
Expected behavior
No panic :)
Environment
- GHC version used: HEAD