Improve kind-checking for 'deriving' clauses

The main payload is in 'mk_functor_like_constraints' in
TcDeriv.inferConstraints.

This is moving towards a fix for Trac #10561

6 files changed, 31 insertions, 15 deletions

diff --git a/testsuite/tests/deriving/should_compile/T10561.hs b/testsuite/tests/deriving/should_compile/T10561.hs
new file mode 100644
index 0000000000..85acc516d9
--- /dev/null
+++ b/testsuite/tests/deriving/should_compile/T10561.hs
@@ -0,0 +1,19 @@
+{-# LANGUAGE PolyKinds, DeriveFunctor, RankNTypes #-}
+
+module T10561 where
+
+-- Ultimately this should "Just Work",
+-- but in GHC 7.10 it gave a Lint failure
+-- For now (HEAD, Jun 2015) it gives a kind error message,
+-- which is better than a crash
+
+newtype Compose f g a = Compose (f (g a)) deriving Functor
+
+{-
+instance forall   (f_ant :: k_ans -> *)
+                  (g_anu :: * -> k_ans).
+           (Functor f_ant, Functor g_anu) =>
+             Functor (Compose f_ant g_anu) where
+    fmap f_anv (T10561.Compose a1_anw)
+      = Compose (fmap (fmap f_anv) a1_anw)
+-}
diff --git a/testsuite/tests/deriving/should_compile/T10561.stderr b/testsuite/tests/deriving/should_compile/T10561.stderr
new file mode 100644
index 0000000000..3a158ddb9a
--- /dev/null
+++ b/testsuite/tests/deriving/should_compile/T10561.stderr
@@ -0,0 +1,5 @@
+
+T10561.hs:10:52: error:
+    Couldn't match kind ‘k’ with ‘*’
+      arising from the first field of ‘Compose’ (type ‘f (g a)’)
+    When deriving the instance for (Functor (Compose f g))
diff --git a/testsuite/tests/deriving/should_compile/all.T b/testsuite/tests/deriving/should_compile/all.T
index e16d8f5432..a01a5149b2 100644
--- a/testsuite/tests/deriving/should_compile/all.T
+++ b/testsuite/tests/deriving/should_compile/all.T
@@ -53,4 +53,5 @@ test('T9069', normal, compile, [''])
 test('T9359', normal, compile, [''])
 test('T4896', normal, compile, [''])
 test('T7947', extra_clean(['T7947a.o', 'T7947a.hi', 'T7947b.o', 'T7947b.hi']), multimod_compile, ['T7947', '-v0'])
+test('T10561', normal, compile_fail, [''])
 
diff --git a/testsuite/tests/deriving/should_fail/T9071.stderr b/testsuite/tests/deriving/should_fail/T9071.stderr
index 3a09c8ecd5..c2dccbd28f 100644
--- a/testsuite/tests/deriving/should_fail/T9071.stderr
+++ b/testsuite/tests/deriving/should_fail/T9071.stderr
@@ -1,10 +1,7 @@
 [1 of 2] Compiling T9071a           ( T9071a.hs, T9071a.o )
 [2 of 2] Compiling T9071            ( T9071.hs, T9071.o )
 
-T9071.hs:7:37:
-    No instance for (Functor Mu)
+T9071.hs:7:37: error:
+    Couldn't match kind ‘* -> *’ with ‘*’
       arising from the first field of ‘F’ (type ‘Mu (K a)’)
-    Possible fix:
-      use a standalone 'deriving instance' declaration,
-        so you can specify the instance context yourself
     When deriving the instance for (Functor F)
diff --git a/testsuite/tests/deriving/should_fail/T9071_2.stderr b/testsuite/tests/deriving/should_fail/T9071_2.stderr
index 65ba471c40..f618343a7a 100644
--- a/testsuite/tests/deriving/should_fail/T9071_2.stderr
+++ b/testsuite/tests/deriving/should_fail/T9071_2.stderr
@@ -1,8 +1,5 @@
 
-T9071_2.hs:7:40:
-    No instance for (Functor K1)
+T9071_2.hs:7:40: error:
+    Couldn't match kind ‘* -> *’ with ‘*’
       arising from the first field of ‘F1’ (type ‘Mu (K1 a)’)
-    Possible fix:
-      use a standalone 'deriving instance' declaration,
-        so you can specify the instance context yourself
     When deriving the instance for (Functor F1)
diff --git a/testsuite/tests/typecheck/should_fail/T9305.stderr b/testsuite/tests/typecheck/should_fail/T9305.stderr
index c908a562ae..e7c761ef46 100644
--- a/testsuite/tests/typecheck/should_fail/T9305.stderr
+++ b/testsuite/tests/typecheck/should_fail/T9305.stderr
@@ -1,8 +1,5 @@
 
-T9305.hs:8:48:
-    No instance for (Functor F)
+T9305.hs:8:48: error:
+    Couldn't match kind ‘* -> *’ with ‘*’
       arising from the first field of ‘EventF’ (type ‘F (Event a)’)
-    Possible fix:
-      use a standalone 'deriving instance' declaration,
-        so you can specify the instance context yourself
     When deriving the instance for (Functor EventF)