Pmc: Add regression test for #19622

It appears that the issue has already been fixed. Judging by the use of
a pattern synonym with a provided constraint, my bet is on 1793ca9d.

Fixes #19622.

testsuite/tests/pmcheck/should_compile/T19622.hs

+{-# LANGUAGE GADTs                     #-}
+{-# LANGUAGE PatternSynonyms           #-}
+{-# LANGUAGE RankNTypes                #-}
+{-# LANGUAGE TypeInType                #-}
+{-# LANGUAGE TypeOperators             #-}
+{-# LANGUAGE ViewPatterns              #-}
+
+module T19622 where
+
+import Data.Kind (Type)
+
+data A
+data B
+
+data ElemKind k where
+  ElemKindA :: ElemKind A
+  ElemKindB :: ElemKind B
+
+class KnownElemKind (xs :: [k]) where
+  getKind :: TypedList f xs -> ElemKind k
+
+data TypedList (f :: (k -> Type)) (xs :: [k]) where
+  Nil :: TypedList f '[]
+  Cons :: f x -> TypedList f xs -> TypedList f (x ': xs)
+
+data Dim (x :: k)
+
+pattern DimA :: forall k (xs :: [k]) . KnownElemKind xs => (k ~ A) => TypedList Dim xs
+pattern DimA <- (getKind -> ElemKindA)
+
+{-# COMPLETE DimA #-}
+{-# COMPLETE Nil, Cons #-}
+
+f :: forall (xns :: [B]) . TypedList Dim xns -> TypedList Dim xns -> Bool
+f Nil Nil = True
+f (Cons _ _) (Cons _ _) = True
+
+g :: forall (xns :: [B]) . TypedList Dim xns -> Bool
+g Nil = True
+g (Cons _ _) = True
+
+h :: forall (xns :: [A]) . TypedList Dim xns -> Bool
+h Nil = True
+h (Cons _ _) = True
+
+i :: forall (xns :: [A]) . TypedList Dim xns -> TypedList Dim xns -> Bool
+i Nil Nil = True
+i (Cons _ _) (Cons _ _) = True
+
+j :: forall k (xns :: [k]) . TypedList Dim xns -> TypedList Dim xns -> Bool
+j Nil Nil = True
+j (Cons _ _) (Cons _ _) = True
+
+l :: forall (xns :: [A]) . KnownElemKind xns => TypedList Dim xns -> Bool
+l DimA = True

testsuite/tests/pmcheck/should_compile/all.T

@@ -162,6 +162,8 @@ test('T18708', normal, compile,
      ['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
 test('T18932', normal, compile,
      ['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
+test('T19622', normal, compile,
+     ['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
 
 # Other tests
 test('pmc001', [], compile,