Fix #11711.

There were two bugs here, both simple: we need to filter out
covars before calling isMetaTyVar in the solver, and TcPat had
a tcSubType the wrong way round.

test case: dependent/should_compile/T11711

3 files changed, 69 insertions, 10 deletions

diff --git a/testsuite/tests/dependent/should_compile/T11711.hs b/testsuite/tests/dependent/should_compile/T11711.hs
new file mode 100644
index 0000000000..633ae35e64
--- /dev/null
+++ b/testsuite/tests/dependent/should_compile/T11711.hs
@@ -0,0 +1,58 @@
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE KindSignatures #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE TypeInType #-}
+{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE FlexibleInstances #-}
+
+module T11711 where
+
+import Data.Kind (Type)
+
+data (:~~:) (a :: k1) (b :: k2) where
+    HRefl :: a :~~: a
+
+data TypeRep (a :: k) where
+    TrTyCon :: String -> TypeRep k -> TypeRep (a :: k)
+    TrApp   :: forall k1 k2 (a :: k1 -> k2) (b :: k1).
+               TypeRep (a :: k1 -> k2)
+            -> TypeRep (b :: k1)
+            -> TypeRep (a b)
+
+class Typeable (a :: k) where
+    typeRep :: TypeRep a
+
+data TypeRepX where
+    TypeRepX :: forall k (a :: k). TypeRep a -> TypeRepX
+
+eqTypeRep :: TypeRep a -> TypeRep b -> Maybe (a :~~: b)
+eqTypeRep = undefined
+
+typeRepKind :: forall k (a :: k). TypeRep a -> TypeRep k
+typeRepKind = undefined
+
+instance Typeable Type where
+  typeRep = TrTyCon "Type" typeRep
+
+funResultTy :: TypeRepX -> TypeRepX -> Maybe TypeRepX
+funResultTy (TypeRepX f) (TypeRepX x)
+  | Just HRefl <- (typeRep :: TypeRep Type) `eqTypeRep` typeRepKind f
+  , TRFun arg res <- f
+  , Just HRefl <- arg `eqTypeRep` x
+  = Just (TypeRepX res)
+  | otherwise
+  = Nothing
+
+trArrow :: TypeRep (->)
+trArrow = undefined
+
+pattern TRFun :: forall fun. ()
+              => forall arg res. (fun ~ (arg -> res))
+              => TypeRep arg
+              -> TypeRep res
+              -> TypeRep fun
+pattern TRFun arg res <- TrApp (TrApp (eqTypeRep trArrow -> Just HRefl) arg) res
diff --git a/testsuite/tests/dependent/should_compile/all.T b/testsuite/tests/dependent/should_compile/all.T
index 783fa16f55..8ecd105a09 100644
--- a/testsuite/tests/dependent/should_compile/all.T
+++ b/testsuite/tests/dependent/should_compile/all.T
@@ -17,3 +17,4 @@ test('dynamic-paper', expect_fail_for(['optasm', 'optllvm']), compile, [''])
 test('T11311', normal, compile, [''])
 test('T11405', normal, compile, [''])
 test('T11241', normal, compile, [''])
+test('T11711', normal, compile, [''])
diff --git a/testsuite/tests/patsyn/should_fail/mono.stderr b/testsuite/tests/patsyn/should_fail/mono.stderr
index 2bed60eafb..20714e7565 100644
--- a/testsuite/tests/patsyn/should_fail/mono.stderr
+++ b/testsuite/tests/patsyn/should_fail/mono.stderr
@@ -1,12 +1,12 @@
 
-mono.hs:7:4:
-    Couldn't match type ‘Int’ with ‘Bool’
-    Expected type: [Bool]
-      Actual type: [Int]
-    In the pattern: Single x
-    In an equation for ‘f’: f (Single x) = x
+mono.hs:7:4: error:
+    • Couldn't match type ‘Bool’ with ‘Int’
+      Expected type: [Int]
+        Actual type: [Bool]
+    • In the pattern: Single x
+      In an equation for ‘f’: f (Single x) = x
 
-mono.hs:7:16:
-    Couldn't match expected type ‘Bool’ with actual type ‘Int’
-    In the expression: x
-    In an equation for ‘f’: f (Single x) = x
+mono.hs:7:16: error:
+    • Couldn't match expected type ‘Bool’ with actual type ‘Int’
+    • In the expression: x
+      In an equation for ‘f’: f (Single x) = x