Improve error message for Typeable k (T k)

GHC can't yest build a TypeRep for a type involving kind variables.
(We await kinds = types for that.)  But the error message was terrible,
as fixing #10524 reminded me.

This improves it a lot.

16 files changed, 138 insertions, 154 deletions

diff --git a/compiler/typecheck/TcErrors.hs b/compiler/typecheck/TcErrors.hs
index 3af562be76..032af20b16 100644
--- a/compiler/typecheck/TcErrors.hs
+++ b/compiler/typecheck/TcErrors.hs
@@ -27,6 +27,8 @@ import DataCon
 import TcEvidence
 import Name
 import RdrName ( lookupGRE_Name, GlobalRdrEnv, mkRdrUnqual )
+import Class( className )
+import PrelNames( typeableClassName )
 import Id
 import Var
 import VarSet
@@ -1342,6 +1344,7 @@ mk_dict_err ctxt (ct, (matches, unifiers, unsafe_overlapped))
 
     cannot_resolve_msg ct binds_msg
       = vcat [ addArising orig no_inst_msg
+             , nest 2 extra_note
              , vcat (pp_givens givens)
              , ppWhen (has_ambig_tvs && not (null unifiers && null givens))
                (vcat [ ambig_msg, binds_msg, potential_msg ])
@@ -1376,22 +1379,19 @@ mk_dict_err ctxt (ct, (matches, unifiers, unsafe_overlapped))
     ppr_skol skol_info      = ppr skol_info
 
     no_inst_msg
-      | null givens && null matches
-      = ptext (sLit "No instance for")
-        <+> pprParendType pred
-        $$ if type_has_arrow pred
-            then nest 2 $ ptext (sLit "(maybe you haven't applied a function to enough arguments?)")
-            else empty
-
-      | otherwise
-      = ptext (sLit "Could not deduce") <+> pprParendType pred
-
-    type_has_arrow (TyVarTy _)      = False
-    type_has_arrow (AppTy t1 t2)    = type_has_arrow t1 || type_has_arrow t2
-    type_has_arrow (TyConApp _ ts)  = or $ map type_has_arrow ts
-    type_has_arrow (FunTy _ _)      = True
-    type_has_arrow (ForAllTy _ t)   = type_has_arrow t
-    type_has_arrow (LitTy _)        = False
+      | null givens && null matches = ptext (sLit "No instance for")  <+> pprParendType pred
+      | otherwise                   = ptext (sLit "Could not deduce") <+> pprParendType pred
+
+    extra_note | any isFunTy (filterOut isKind tys)
+               = ptext (sLit "(maybe you haven't applied a function to enough arguments?)")
+               | className clas == typeableClassName  -- Avoid mysterious "No instance for (Typeable T)
+               , [_,ty] <- tys                        -- Look for (Typeable (k->*) (T k))
+               , Just (tc,_) <- tcSplitTyConApp_maybe ty
+               , not (isTypeFamilyTyCon tc)
+               = hang (ptext (sLit "GHC can't yet do polykinded"))
+                    2 (ptext (sLit "Typeable") <+> parens (ppr ty <+> dcolon <+> ppr (typeKind ty)))
+               | otherwise
+               = empty
 
     drv_fixes = case orig of
                    DerivOrigin      -> [drv_fix]
diff --git a/testsuite/tests/annotations/should_fail/annfail08.stderr b/testsuite/tests/annotations/should_fail/annfail08.stderr
index 2a9980dcb6..66e9c7e29b 100644
--- a/testsuite/tests/annotations/should_fail/annfail08.stderr
+++ b/testsuite/tests/annotations/should_fail/annfail08.stderr
@@ -1,12 +1,10 @@
-

-annfail08.hs:9:1:

-    No instance for (Data (a0 -> a0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from an annotation

-    In the annotation: {-# ANN f (id + 1) #-}

-

-annfail08.hs:9:15:

-    No instance for (Num (a0 -> a0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘+’

-    In the annotation: {-# ANN f (id + 1) #-}

+
+annfail08.hs:9:1: error:
+    No instance for (Data (a0 -> a0)) arising from an annotation
+      (maybe you haven't applied a function to enough arguments?)
+    In the annotation: {-# ANN f (id + 1) #-}
+
+annfail08.hs:9:15: error:
+    No instance for (Num (a0 -> a0)) arising from a use of ‘+’
+      (maybe you haven't applied a function to enough arguments?)
+    In the annotation: {-# ANN f (id + 1) #-}
diff --git a/testsuite/tests/deriving/should_fail/drvfail007.stderr b/testsuite/tests/deriving/should_fail/drvfail007.stderr
index ad43243eb0..f786f336be 100644
--- a/testsuite/tests/deriving/should_fail/drvfail007.stderr
+++ b/testsuite/tests/deriving/should_fail/drvfail007.stderr
@@ -1,9 +1,9 @@
-

-drvfail007.hs:4:38:

-    No instance for (Eq (Int -> Int))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from the first field of ‘Foo’ (type ‘Int -> Int’)

-    Possible fix:

-      use a standalone 'deriving instance' declaration,

-        so you can specify the instance context yourself

-    When deriving the instance for (Eq Foo)

+
+drvfail007.hs:4:38: error:
+    No instance for (Eq (Int -> Int))
+      arising from the first field of ‘Foo’ (type ‘Int -> Int’)
+      (maybe you haven't applied a function to enough arguments?)
+    Possible fix:
+      use a standalone 'deriving instance' declaration,
+        so you can specify the instance context yourself
+    When deriving the instance for (Eq Foo)
diff --git a/testsuite/tests/driver/T2182.stderr b/testsuite/tests/driver/T2182.stderr
index d88f6c0057..0585e4c701 100644
--- a/testsuite/tests/driver/T2182.stderr
+++ b/testsuite/tests/driver/T2182.stderr
@@ -1,28 +1,24 @@
-

-T2182.hs:5:5:

-    No instance for (Show (t1 -> t1))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘show’

-    In the expression: show (\ x -> x)

-    In an equation for ‘y’: y = show (\ x -> x)

-

-T2182.hs:6:15:

-    No instance for (Eq (t0 -> t0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘==’

-    In the expression: (\ x -> x) == (\ y -> y)

-    In an equation for ‘z’: z = (\ x -> x) == (\ y -> y)

-

-T2182.hs:5:5:

-    No instance for (Show (t1 -> t1))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘show’

-    In the expression: show (\ x -> x)

-    In an equation for ‘y’: y = show (\ x -> x)

-

-T2182.hs:6:15:

-    No instance for (Eq (t0 -> t0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘==’

-    In the expression: (\ x -> x) == (\ y -> y)

-    In an equation for ‘z’: z = (\ x -> x) == (\ y -> y)

+
+T2182.hs:5:5: error:
+    No instance for (Show (t1 -> t1)) arising from a use of ‘show’
+      (maybe you haven't applied a function to enough arguments?)
+    In the expression: show (\ x -> x)
+    In an equation for ‘y’: y = show (\ x -> x)
+
+T2182.hs:6:15: error:
+    No instance for (Eq (t0 -> t0)) arising from a use of ‘==’
+      (maybe you haven't applied a function to enough arguments?)
+    In the expression: (\ x -> x) == (\ y -> y)
+    In an equation for ‘z’: z = (\ x -> x) == (\ y -> y)
+
+T2182.hs:5:5: error:
+    No instance for (Show (t1 -> t1)) arising from a use of ‘show’
+      (maybe you haven't applied a function to enough arguments?)
+    In the expression: show (\ x -> x)
+    In an equation for ‘y’: y = show (\ x -> x)
+
+T2182.hs:6:15: error:
+    No instance for (Eq (t0 -> t0)) arising from a use of ‘==’
+      (maybe you haven't applied a function to enough arguments?)
+    In the expression: (\ x -> x) == (\ y -> y)
+    In an equation for ‘z’: z = (\ x -> x) == (\ y -> y)
diff --git a/testsuite/tests/ghci.debugger/scripts/break003.stderr b/testsuite/tests/ghci.debugger/scripts/break003.stderr
index fee6366347..00d4237e49 100644
--- a/testsuite/tests/ghci.debugger/scripts/break003.stderr
+++ b/testsuite/tests/ghci.debugger/scripts/break003.stderr
@@ -1,6 +1,5 @@
-

-<interactive>:5:1:

-    No instance for (Show (t -> t1))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘print’

-    In a stmt of an interactive GHCi command: print it

+
+<interactive>:5:1: error:
+    No instance for (Show (t -> t1)) arising from a use of ‘print’
+      (maybe you haven't applied a function to enough arguments?)
+    In a stmt of an interactive GHCi command: print it
diff --git a/testsuite/tests/ghci/scripts/Defer02.stderr b/testsuite/tests/ghci/scripts/Defer02.stderr
index a3a3e9d061..b5b3373489 100644
--- a/testsuite/tests/ghci/scripts/Defer02.stderr
+++ b/testsuite/tests/ghci/scripts/Defer02.stderr
@@ -26,9 +26,8 @@
     In an equation for ‘c’: c (C2 x) = True
 
 ../../typecheck/should_run/Defer01.hs:28:5: warning:
-    No instance for (Num (a -> a))
+    No instance for (Num (a -> a)) arising from the literal ‘1’
       (maybe you haven't applied a function to enough arguments?)
-      arising from the literal ‘1’
     In the expression: 1
     In an equation for ‘d’: d = 1
 
@@ -136,9 +135,8 @@
     In the first argument of ‘c’, namely ‘(C2 True)’
     In the first argument of ‘print’, namely ‘(c (C2 True))’
 *** Exception: ../../typecheck/should_run/Defer01.hs:28:5: error:
-    No instance for (Num (a -> a))
+    No instance for (Num (a -> a)) arising from the literal ‘1’
       (maybe you haven't applied a function to enough arguments?)
-      arising from the literal ‘1’
     In the expression: 1
     In an equation for ‘d’: d = 1
 (deferred type error)
diff --git a/testsuite/tests/ghci/scripts/T2182ghci.stderr b/testsuite/tests/ghci/scripts/T2182ghci.stderr
index 6a6eebded2..470e72945d 100644
--- a/testsuite/tests/ghci/scripts/T2182ghci.stderr
+++ b/testsuite/tests/ghci/scripts/T2182ghci.stderr
@@ -1,30 +1,25 @@
-

-<interactive>:3:1:

-    No instance for (Show (t0 -> t0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘print’

-    In a stmt of an interactive GHCi command: print it

-

-<interactive>:11:1:

-    No instance for (Show (t0 -> t0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘print’

-    In a stmt of an interactive GHCi command: print it

-

-<interactive>:20:1:

-    No instance for (Show (t0 -> t0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘print’

-    In a stmt of an interactive GHCi command: print it

-

-<interactive>:29:1:

-    No instance for (Show (t0 -> t0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘print’

-    In a stmt of an interactive GHCi command: print it

-

-<interactive>:50:1:

-    No instance for (Show (t0 -> t0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘print’

-    In a stmt of an interactive GHCi command: print it

+
+<interactive>:3:1: error:
+    No instance for (Show (t0 -> t0)) arising from a use of ‘print’
+      (maybe you haven't applied a function to enough arguments?)
+    In a stmt of an interactive GHCi command: print it
+
+<interactive>:11:1: error:
+    No instance for (Show (t0 -> t0)) arising from a use of ‘print’
+      (maybe you haven't applied a function to enough arguments?)
+    In a stmt of an interactive GHCi command: print it
+
+<interactive>:20:1: error:
+    No instance for (Show (t0 -> t0)) arising from a use of ‘print’
+      (maybe you haven't applied a function to enough arguments?)
+    In a stmt of an interactive GHCi command: print it
+
+<interactive>:29:1: error:
+    No instance for (Show (t0 -> t0)) arising from a use of ‘print’
+      (maybe you haven't applied a function to enough arguments?)
+    In a stmt of an interactive GHCi command: print it
+
+<interactive>:50:1: error:
+    No instance for (Show (t0 -> t0)) arising from a use of ‘print’
+      (maybe you haven't applied a function to enough arguments?)
+    In a stmt of an interactive GHCi command: print it
diff --git a/testsuite/tests/partial-sigs/should_fail/AnnotatedConstraint.stderr b/testsuite/tests/partial-sigs/should_fail/AnnotatedConstraint.stderr
index ef66e7539d..979651bcea 100644
--- a/testsuite/tests/partial-sigs/should_fail/AnnotatedConstraint.stderr
+++ b/testsuite/tests/partial-sigs/should_fail/AnnotatedConstraint.stderr
@@ -1,7 +1,6 @@
-

-AnnotatedConstraint.hs:7:8:

-    No instance for (Eq (a0 -> a0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘foo’

-    In the expression: foo id

-    In an equation for ‘test’: test = foo id

+
+AnnotatedConstraint.hs:7:8: error:
+    No instance for (Eq (a0 -> a0)) arising from a use of ‘foo’
+      (maybe you haven't applied a function to enough arguments?)
+    In the expression: foo id
+    In an equation for ‘test’: test = foo id
diff --git a/testsuite/tests/rebindable/rebindable6.stderr b/testsuite/tests/rebindable/rebindable6.stderr
index 10c8f56ee3..9e3dc0a5c7 100644
--- a/testsuite/tests/rebindable/rebindable6.stderr
+++ b/testsuite/tests/rebindable/rebindable6.stderr
@@ -1,8 +1,8 @@
 
-rebindable6.hs:106:17:
+rebindable6.hs:106:17: error:
     No instance for (HasSeq (IO a -> t0 -> IO b))
-      (maybe you haven't applied a function to enough arguments?)
       arising from a do statement
+      (maybe you haven't applied a function to enough arguments?)
     The type variable ‘t0’ is ambiguous
     Relevant bindings include
       g :: IO (Maybe b) (bound at rebindable6.hs:104:19)
@@ -23,10 +23,10 @@ rebindable6.hs:106:17:
                  Just (b :: b) <- g;
                  return b }
 
-rebindable6.hs:107:17:
+rebindable6.hs:107:17: error:
     No instance for (HasFail ([Char] -> t1))
-      (maybe you haven't applied a function to enough arguments?)
       arising from a do statement
+      (maybe you haven't applied a function to enough arguments?)
     The type variable ‘t1’ is ambiguous
     Note: there is a potential instance available:
       instance HasFail (String -> IO a)
@@ -42,10 +42,10 @@ rebindable6.hs:107:17:
                  Just (b :: b) <- g;
                  return b }
 
-rebindable6.hs:108:17:
+rebindable6.hs:108:17: error:
     No instance for (HasReturn (b -> t1))
-      (maybe you haven't applied a function to enough arguments?)
       arising from a use of ‘return’
+      (maybe you haven't applied a function to enough arguments?)
     The type variable ‘t1’ is ambiguous
     Relevant bindings include
       b :: b (bound at rebindable6.hs:107:23)
diff --git a/testsuite/tests/typecheck/should_fail/T2846b.stderr b/testsuite/tests/typecheck/should_fail/T2846b.stderr
index 3008346ddd..0323283477 100644
--- a/testsuite/tests/typecheck/should_fail/T2846b.stderr
+++ b/testsuite/tests/typecheck/should_fail/T2846b.stderr
@@ -1,7 +1,6 @@
-

-T2846b.hs:5:5:

-    No instance for (Show (Num a0 => a0))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘show’

-    In the expression: show ([1, 2, 3] :: [Num a => a])

-    In an equation for ‘f’: f = show ([1, 2, 3] :: [Num a => a])

+
+T2846b.hs:5:5: error:
+    No instance for (Show (Num a0 => a0)) arising from a use of ‘show’
+      (maybe you haven't applied a function to enough arguments?)
+    In the expression: show ([1, 2, 3] :: [Num a => a])
+    In an equation for ‘f’: f = show ([1, 2, 3] :: [Num a => a])
diff --git a/testsuite/tests/typecheck/should_fail/T6022.stderr b/testsuite/tests/typecheck/should_fail/T6022.stderr
index 7d12b8f358..a85c6289da 100644
--- a/testsuite/tests/typecheck/should_fail/T6022.stderr
+++ b/testsuite/tests/typecheck/should_fail/T6022.stderr
@@ -1,7 +1,6 @@
-

-T6022.hs:3:9: error:

-    No instance for (Eq ([a] -> a))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘==’

-    In the expression: x == head

-    In an equation for ‘f’: f x = x == head

+
+T6022.hs:3:9: error:
+    No instance for (Eq ([a] -> a)) arising from a use of ‘==’
+      (maybe you haven't applied a function to enough arguments?)
+    In the expression: x == head
+    In an equation for ‘f’: f x = x == head
diff --git a/testsuite/tests/typecheck/should_fail/T9858a.stderr b/testsuite/tests/typecheck/should_fail/T9858a.stderr
index 61c62eaeec..a42339ed78 100644
--- a/testsuite/tests/typecheck/should_fail/T9858a.stderr
+++ b/testsuite/tests/typecheck/should_fail/T9858a.stderr
@@ -1,14 +1,14 @@
-

-T9858a.hs:28:18: error:

-    No instance for (Typeable

-                       ((() :: Constraint, () :: Constraint) => ()))

-      (maybe you haven't applied a function to enough arguments?)

-      arising from a use of ‘cast’

-    In the expression: cast e

-    In the expression: case cast e of { Just e' -> ecast e' }

-    In an equation for ‘supercast’:

-        supercast

-          = case cast e of { Just e' -> ecast e' }

-          where

-              e = Refl

-              e :: E PX PX

+
+T9858a.hs:28:18: error:
+    No instance for (Typeable
+                       ((() :: Constraint, () :: Constraint) => ()))
+      arising from a use of ‘cast’
+      (maybe you haven't applied a function to enough arguments?)
+    In the expression: cast e
+    In the expression: case cast e of { Just e' -> ecast e' }
+    In an equation for ‘supercast’:
+        supercast
+          = case cast e of { Just e' -> ecast e' }
+          where
+              e = Refl
+              e :: E PX PX
diff --git a/testsuite/tests/typecheck/should_fail/T9858b.stderr b/testsuite/tests/typecheck/should_fail/T9858b.stderr
index b57098e8b4..656ff53c95 100644
--- a/testsuite/tests/typecheck/should_fail/T9858b.stderr
+++ b/testsuite/tests/typecheck/should_fail/T9858b.stderr
@@ -1,8 +1,8 @@
 
 T9858b.hs:7:8: error:
     No instance for (Typeable (Eq Int => Int))
-      (maybe you haven't applied a function to enough arguments?)
       arising from a use of ‘typeRep’
+      (maybe you haven't applied a function to enough arguments?)
     In the expression: typeRep (Proxy :: Proxy (Eq Int => Int))
     In an equation for ‘test’:
         test = typeRep (Proxy :: Proxy (Eq Int => Int))
diff --git a/testsuite/tests/typecheck/should_fail/T9999.stderr b/testsuite/tests/typecheck/should_fail/T9999.stderr
index ae7fa28123..0defd090b0 100644
--- a/testsuite/tests/typecheck/should_fail/T9999.stderr
+++ b/testsuite/tests/typecheck/should_fail/T9999.stderr
@@ -1,8 +1,7 @@
 
-T9999.hs:13:38:
-    No instance for (Typeable F1)
-      (maybe you haven't applied a function to enough arguments?)
-      arising from a use of ‘typeRep’
+T9999.hs:13:38: error:
+    No instance for (Typeable F1) arising from a use of ‘typeRep’
+      GHC can't yet do polykinded Typeable (F1 :: k0 -> *)
     In the second argument of ‘(==)’, namely
       ‘typeRep (Proxy :: Proxy F1)’
     In the expression:
diff --git a/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.stderr b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.stderr
index 84e0862056..f63fb47789 100644
--- a/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.stderr
+++ b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.stderr
@@ -7,7 +7,7 @@ TcStaticPointersFail02.hs:9:6: error:
 
 TcStaticPointersFail02.hs:12:6: error:
     No instance for (Typeable (Monad m => a -> m a))
-      (maybe you haven't applied a function to enough arguments?)
       arising from a static form
+      (maybe you haven't applied a function to enough arguments?)
     In the expression: static return
     In an equation for ‘f2’: f2 = static return
diff --git a/testsuite/tests/typecheck/should_fail/tcfail046.stderr b/testsuite/tests/typecheck/should_fail/tcfail046.stderr
index 1dbfdad8f3..c144130fe4 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail046.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail046.stderr
@@ -1,15 +1,17 @@
 
-tcfail046.hs:10:50:
+tcfail046.hs:10:50: error:
     No instance for (Eq (Process a))
       arising from the first field of ‘Do’ (type ‘Process a’)
+      (maybe you haven't applied a function to enough arguments?)
     Possible fix:
       use a standalone 'deriving instance' declaration,
         so you can specify the instance context yourself
     When deriving the instance for (Eq (Continuation a))
 
-tcfail046.hs:22:25:
+tcfail046.hs:22:25: error:
     No instance for (Eq (Process a))
       arising from the first field of ‘Create’ (type ‘Process a’)
+      (maybe you haven't applied a function to enough arguments?)
     Possible fix:
       use a standalone 'deriving instance' declaration,
         so you can specify the instance context yourself