Synchronize ClsInst.doTyConApp with TcTypeable validity checks (#15862)

Issue #15862 demonstrated examples of type constructors on which
`TcTypeable.tyConIsTypeable` would return `False`, but the `Typeable`
constraint solver in `ClsInst` (in particular, `doTyConApp`) would
try to generate `Typeable` evidence for anyway, resulting in
disaster. This incongruity was caused by the fact that `doTyConApp`
was using a weaker validity check than `tyConIsTypeable` to determine
if a type constructor warrants `Typeable` evidence or not. The
solution, perhaps unsurprisingly, is to use `tyConIsTypeable` in
`doTyConApp` instead.

To avoid import cycles between `ClsInst` and `TcTypeable`, I factored
out `tyConIsTypeable` into its own module, `TcTypeableValidity`.

Fixes #15862.

1 files changed, 36 insertions, 0 deletions

diff --git a/testsuite/tests/typecheck/should_fail/T15862.hs b/testsuite/tests/typecheck/should_fail/T15862.hs
new file mode 100644
index 0000000000..c98b5939d1
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T15862.hs
@@ -0,0 +1,36 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE ImpredicativeTypes #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE UnboxedSums #-}
+module Bug where
+
+import Data.Kind
+import Type.Reflection
+
+newtype Foo = MkFoo (forall a. a)
+
+foo :: TypeRep MkFoo
+foo = typeRep @MkFoo
+
+type family F a
+type instance F Int = Type
+
+data Bar = forall (a :: F Int). MkBar a
+
+bar :: TypeRep (MkBar True)
+bar = typeRep
+
+data Quux = MkQuux (# Bool | Int #)
+
+quux :: TypeRep MkQuux
+quux = typeRep
+
+data Quuz :: (Type ~ Type) => Type where
+  MkQuuz :: Quuz
+
+quuz :: TypeRep MkQuuz
+quuz = typeRep