1 files changed, 39 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_fail/T23308.hs b/testsuite/tests/typecheck/should_fail/T23308.hs
new file mode 100644
index 0000000000..c5b55ee2d2
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+++ b/testsuite/tests/typecheck/should_fail/T23308.hs
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+{-# LANGUAGE DataKinds, UnliftedNewtypes, TypeFamilies #-}
+
+module T23308 where
+
+import Data.Proxy
+import GHC.Exts
+
+-- Check that we don't panic in the middle of typechecking
+-- when there is an invalid newtype in a knot-tied group of TyCons.
+
+data A1 = A1 !B1
+newtype B1 = B1 C1 C1
+data C1 = C1 A1
+
+
+data A2 = A2 !B2
+newtype B2 where { B2 :: forall (x :: C2). Proxy x -> B2 }
+data C2 = C2 A2
+
+type F2' :: forall {k}. k -> TYPE WordRep
+type family F2' a where {}
+data A2' = A2' !B2'
+newtype B2' where { B2' :: forall (x :: C2'). F2' x -> B2' }
+data C2' = C2' A2'
+
+
+data A3 = A3 !B3
+newtype B3 where { B3 :: forall (x :: C2). B2 }
+data C3 = C3 A3
+
+
+data A4 = A4 !(B4 Int)
+newtype B4 a where { B4 :: C4 -> B4 Int }
+data C4 = C4 A4
+
+
+data A5 = A5 !(B5 Int)
+newtype B5 a where { B5 :: Num a => B5 (a, a) }
+data C5 = C5 A5