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

4 files changed, 17 insertions, 13 deletions

diff --git a/testsuite/tests/partial-sigs/should_compile/T13482.hs b/testsuite/tests/partial-sigs/should_compile/T13482.hs
index 3af3a74231..0a2c619f66 100644
--- a/testsuite/tests/partial-sigs/should_compile/T13482.hs
+++ b/testsuite/tests/partial-sigs/should_compile/T13482.hs
@@ -5,10 +5,12 @@
 
 module T12382 where
 
+import Data.Kind (Type)
+
 minimal1_noksig :: forall m. ( _ ) => Int -> Bool
 minimal1_noksig _ = (mempty :: m) == (mempty :: m)
 
-minimal1 :: forall (m :: *). _ => Bool
+minimal1 :: forall (m :: Type). _ => Bool
 minimal1 = (mempty :: m) == (mempty :: m)
 
 minimal2 :: forall m. (Eq m, _) => Bool
diff --git a/testsuite/tests/partial-sigs/should_compile/T13482.stderr b/testsuite/tests/partial-sigs/should_compile/T13482.stderr
index dd46400b1a..a21b7dcac4 100644
--- a/testsuite/tests/partial-sigs/should_compile/T13482.stderr
+++ b/testsuite/tests/partial-sigs/should_compile/T13482.stderr
@@ -1,31 +1,31 @@
 
-T13482.hs:8:32: warning: [-Wpartial-type-signatures (in -Wdefault)]
+T13482.hs:10:32: warning: [-Wpartial-type-signatures (in -Wdefault)]
     • Found type wildcard ‘_’ standing for ‘(Eq m, Monoid m)’
       Where: ‘m’ is a rigid type variable bound by
                the inferred type of
                  minimal1_noksig :: (Eq m, Monoid m) => Int -> Bool
-               at T13482.hs:9:1-50
+               at T13482.hs:11:1-50
     • In the type signature:
         minimal1_noksig :: forall m. _ => Int -> Bool
 
-T13482.hs:11:30: warning: [-Wpartial-type-signatures (in -Wdefault)]
+T13482.hs:13:33: warning: [-Wpartial-type-signatures (in -Wdefault)]
     • Found type wildcard ‘_’ standing for ‘(Eq m, Monoid m)’
       Where: ‘m’ is a rigid type variable bound by
                the inferred type of minimal1 :: (Eq m, Monoid m) => Bool
-               at T13482.hs:12:1-41
-    • In the type signature: minimal1 :: forall (m :: *). _ => Bool
+               at T13482.hs:14:1-41
+    • In the type signature: minimal1 :: forall (m :: Type). _ => Bool
 
-T13482.hs:14:30: warning: [-Wpartial-type-signatures (in -Wdefault)]
+T13482.hs:16:30: warning: [-Wpartial-type-signatures (in -Wdefault)]
     • Found type wildcard ‘_’ standing for ‘Monoid m’
       Where: ‘m’ is a rigid type variable bound by
                the inferred type of minimal2 :: (Eq m, Monoid m) => Bool
-               at T13482.hs:15:1-41
+               at T13482.hs:17:1-41
     • In the type signature: minimal2 :: forall m. (Eq m, _) => Bool
 
-T13482.hs:17:34: warning: [-Wpartial-type-signatures (in -Wdefault)]
+T13482.hs:19:34: warning: [-Wpartial-type-signatures (in -Wdefault)]
     • Found type wildcard ‘_’ standing for ‘Eq m’
       Where: ‘m’ is a rigid type variable bound by
                the inferred type of minimal3 :: (Monoid m, Eq m) => Bool
-               at T13482.hs:18:1-41
+               at T13482.hs:20:1-41
     • In the type signature:
         minimal3 :: forall m. (Monoid m, _) => Bool
diff --git a/testsuite/tests/partial-sigs/should_compile/TypeFamilyInstanceLHS.hs b/testsuite/tests/partial-sigs/should_compile/TypeFamilyInstanceLHS.hs
index c3172b7cd0..cd009ca8d5 100644
--- a/testsuite/tests/partial-sigs/should_compile/TypeFamilyInstanceLHS.hs
+++ b/testsuite/tests/partial-sigs/should_compile/TypeFamilyInstanceLHS.hs
@@ -1,7 +1,9 @@
 {-# LANGUAGE TypeFamilies #-}
 module TypeFamilyInstanceLHS where
 
-type family F (a :: *) (b :: *) :: *
+import Data.Kind (Type)
+
+type family F (a :: Type) (b :: Type) :: Type
 type instance F Int  _ = Int
 type instance F Bool _ = Bool
 
diff --git a/testsuite/tests/partial-sigs/should_compile/TypeFamilyInstanceLHS.stderr b/testsuite/tests/partial-sigs/should_compile/TypeFamilyInstanceLHS.stderr
index 1a783cba74..76c5b3fbc3 100644
--- a/testsuite/tests/partial-sigs/should_compile/TypeFamilyInstanceLHS.stderr
+++ b/testsuite/tests/partial-sigs/should_compile/TypeFamilyInstanceLHS.stderr
@@ -5,9 +5,9 @@ TYPE CONSTRUCTORS
   F :: * -> * -> *
 COERCION AXIOMS
   axiom TypeFamilyInstanceLHS.D:R:FBool_ ::
-    F Bool _ = Bool -- Defined at TypeFamilyInstanceLHS.hs:6:15
+    F Bool _ = Bool -- Defined at TypeFamilyInstanceLHS.hs:8:15
   axiom TypeFamilyInstanceLHS.D:R:FInt_ ::
-    F Int _ = Int -- Defined at TypeFamilyInstanceLHS.hs:5:15
+    F Int _ = Int -- Defined at TypeFamilyInstanceLHS.hs:7:15
 FAMILY INSTANCES
   type instance F Int _
   type instance F Bool _