Enable -Wcompat=error in the testsuite

Enabling -Werror=compat in the testsuite allows us to easily see the
impact that a new warning has on code. It also means that in the period
between adding the warning and making the actual breaking change, all
new test cases that are being added to the testsuite will be
forwards-compatible. This is good because it will make the actual
breaking change contain less irrelevant testsuite updates.

Things that -Wcompat warns about are things that are going to break in
the future, so we can be proactive and keep our testsuite
forwards-compatible.

This patch consists of two main changes:

* Add `TEST_HC_OPTS += -Werror=compat` to the testsuite configuration.
* Fix all broken test cases.

Test Plan: Validate

Reviewers: hvr, goldfire, bgamari, simonpj, RyanGlScott

Reviewed By: goldfire, RyanGlScott

Subscribers: rwbarton, carter

GHC Trac Issues: #15278

Differential Revision: https://phabricator.haskell.org/D5200

5 files changed, 14 insertions, 7 deletions

diff --git a/testsuite/tests/patsyn/should_compile/T10997_1a.hs b/testsuite/tests/patsyn/should_compile/T10997_1a.hs
index f6a292aa54..11af525c53 100644
--- a/testsuite/tests/patsyn/should_compile/T10997_1a.hs
+++ b/testsuite/tests/patsyn/should_compile/T10997_1a.hs
@@ -1,11 +1,11 @@
 {-# LANGUAGE PatternSynonyms, ViewPatterns, ConstraintKinds, TypeFamilies, PolyKinds, KindSignatures #-}
 module T10997_1a where
 
-import GHC.Exts
+import Data.Kind
 
 type family Showable (a :: k) :: Constraint where
-  Showable (a :: *) = (Show a)
-  Showable a       = ()
+  Showable (a :: Type) = (Show a)
+  Showable a           = ()
 
 extractJust :: Maybe a -> (Bool, a)
 extractJust (Just a) = (True, a)
diff --git a/testsuite/tests/patsyn/should_compile/T12968.hs b/testsuite/tests/patsyn/should_compile/T12968.hs
index 99626df1a7..e4b58ed8ac 100644
--- a/testsuite/tests/patsyn/should_compile/T12968.hs
+++ b/testsuite/tests/patsyn/should_compile/T12968.hs
@@ -6,7 +6,8 @@ module T12968 where
 data TypeRep (a :: k)
 
 data TRAppG (fun :: k2) where
-  TRAppG :: forall k1 (a :: k1 -> k2) (b :: k1) . TypeRep a -> TypeRep b -> TRAppG (a b)
+  TRAppG :: forall k1 k2 (a :: k1 -> k2) (b :: k1) .
+            TypeRep a -> TypeRep b -> TRAppG (a b)
 
 pattern TRApp :: forall k2 (fun :: k2). ()
               => forall k1 (a :: k1 -> k2) (b :: k1). (fun ~ a b)
diff --git a/testsuite/tests/patsyn/should_compile/T8966.hs b/testsuite/tests/patsyn/should_compile/T8966.hs
index 895ff1b764..655969e3bb 100644
--- a/testsuite/tests/patsyn/should_compile/T8966.hs
+++ b/testsuite/tests/patsyn/should_compile/T8966.hs
@@ -2,7 +2,9 @@
 
 module T8966 where
 
-data NQ :: [k] -> * where
+import Data.Kind (Type)
+
+data NQ :: [k] -> Type where
    D :: NQ '[a]
 
 pattern Q = D
diff --git a/testsuite/tests/patsyn/should_compile/T8968-1.hs b/testsuite/tests/patsyn/should_compile/T8968-1.hs
index a0e3285a4b..adef52f1ff 100644
--- a/testsuite/tests/patsyn/should_compile/T8968-1.hs
+++ b/testsuite/tests/patsyn/should_compile/T8968-1.hs
@@ -1,7 +1,9 @@
 {-# LANGUAGE GADTs, KindSignatures, PatternSynonyms #-}
 module ShouldCompile where
 
-data X :: (* -> *) -> * -> * where
+import Data.Kind (Type)
+
+data X :: (Type -> Type) -> Type -> Type where
   Y :: f a -> X f (Maybe a)
 
 pattern C :: a -> X Maybe (Maybe a)
diff --git a/testsuite/tests/patsyn/should_compile/T8968-2.hs b/testsuite/tests/patsyn/should_compile/T8968-2.hs
index 0b196a5f88..2ec4d2dfb5 100644
--- a/testsuite/tests/patsyn/should_compile/T8968-2.hs
+++ b/testsuite/tests/patsyn/should_compile/T8968-2.hs
@@ -1,7 +1,9 @@
 {-# LANGUAGE GADTs, KindSignatures, PatternSynonyms, FlexibleContexts #-}
 module ShouldCompile where
 
-data X :: (* -> *) -> * -> * where
+import Data.Kind (Type)
+
+data X :: (Type -> Type) -> Type -> Type where
   Y :: (Show a) => f a -> X f (Maybe a)
 
 pattern C :: (Show (a, Bool)) => a -> X Maybe (Maybe (a, Bool))