Add accurate skolem info when quantifying

Ticket #22379 revealed that skolemiseQuantifiedTyVar was
dropping the passed-in skol_info on the floor when it encountered
a SkolemTv.  Bad!  Several TyCons thereby share a single SkolemInfo
on their binders, which lead to bogus error reports.

3 files changed, 63 insertions, 0 deletions

diff --git a/testsuite/tests/polykinds/T22379a.hs b/testsuite/tests/polykinds/T22379a.hs
new file mode 100644
index 0000000000..d4caa01048
--- /dev/null
+++ b/testsuite/tests/polykinds/T22379a.hs
@@ -0,0 +1,31 @@
+{-# LANGUAGE Haskell2010 #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE TypeFamilies #-}
+module Bug where
+
+import Data.Kind
+import Data.Proxy (Proxy)
+
+data Delayed (env :: Type) (c :: Type)
+data Handler (a :: Type)
+data Router (a :: Type)
+
+-- class decl, then type decl
+
+class HasServer api where
+  type ServerT api (m :: Type -> Type) :: Type
+
+  route ::
+       Proxy api
+    -> Delayed env (Server api)
+    -> Router env
+
+  hoistServerWithContext
+      :: Proxy api
+      -> (forall x. m x -> n x)
+      -> ServerT api m
+      -> ServerT api n
+
+type Server aqi = ServerT aqi Handler
+
diff --git a/testsuite/tests/polykinds/T22379b.hs b/testsuite/tests/polykinds/T22379b.hs
new file mode 100644
index 0000000000..78cd004090
--- /dev/null
+++ b/testsuite/tests/polykinds/T22379b.hs
@@ -0,0 +1,30 @@
+{-# LANGUAGE Haskell2010 #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE TypeFamilies #-}
+module Bug where
+
+import Data.Kind
+import Data.Proxy (Proxy)
+
+data Delayed (env :: Type) (c :: Type)
+data Handler (a :: Type)
+data Router (a :: Type)
+
+-- type decl, then class decl
+
+type Server aqi = ServerT aqi Handler
+
+class HasServer api where
+  type ServerT api (m :: Type -> Type) :: Type
+
+  route ::
+       Proxy api
+    -> Delayed env (Server api)
+    -> Router env
+
+  hoistServerWithContext
+      :: Proxy api
+      -> (forall x. m x -> n x)
+      -> ServerT api m
+      -> ServerT api n
diff --git a/testsuite/tests/polykinds/all.T b/testsuite/tests/polykinds/all.T
index fbe65d4b1c..721e41cebd 100644
--- a/testsuite/tests/polykinds/all.T
+++ b/testsuite/tests/polykinds/all.T
@@ -239,3 +239,5 @@ test('T19739a', normal, compile, [''])
 test('T19739b', normal, compile, [''])
 test('T19739c', normal, compile, [''])
 test('T19739d', normal, compile, [''])
+test('T22379a', normal, compile, [''])
+test('T22379b', normal, compile, [''])