Allow kind-variable binders in type signatures

This is the last major addition to the kind-polymorphism story,
by allowing (Trac #5938)

 type family F a   -- F :: forall k. k -> *
 data T a          -- T :: forall k. k -> *
 type instance F (T (a :: Maybe k)) = Char

The new thing is the explicit 'k' in the type signature on 'a',
which itself is inside a type pattern for F.

Main changes are:

* HsTypes.HsBSig now has a *pair* (kvs, tvs) of binders,
  the kind variables and the type variables

* extractHsTyRdrTyVars returns a pair (kvs, tvs)
  and the function itself has moved from RdrHsSyn to RnTypes

* Quite a bit of fiddling with
     TcHsType.tcHsPatSigType and tcPatSig
  which have become a bit simpler.  I'm still not satisfied
  though.  There's some consequential fiddling in TcRules too.

* Removed the unused HsUtils.collectSigTysFromPats

There's a consequential wibble to Haddock too

3 files changed, 4 insertions, 68 deletions

diff --git a/compiler/parser/Parser.y.pp b/compiler/parser/Parser.y.pp
index 9774c245e7..5fd0e9de76 100644
--- a/compiler/parser/Parser.y.pp
+++ b/compiler/parser/Parser.y.pp
@@ -729,7 +729,7 @@ data_or_newtype :: { Located NewOrData }
 
 opt_kind_sig :: { Located (Maybe (HsBndrSig (LHsKind RdrName))) }
         :                               { noLoc Nothing }
-        | '::' kind                     { LL (Just (HsBSig $2 placeHolderBndrs)) }
+        | '::' kind                     { LL (Just (mkHsBSig $2)) }
 
 -- tycl_hdr parses the header of a class or data type decl,
 -- which takes the form
@@ -876,7 +876,7 @@ rule_var_list :: { [RuleBndr RdrName] }
 
 rule_var :: { RuleBndr RdrName }
         : varid                                 { RuleBndr $1 }
-        | '(' varid '::' ctype ')'              { RuleBndrSig $2 (HsBSig $4 placeHolderBndrs) }
+        | '(' varid '::' ctype ')'              { RuleBndrSig $2 (mkHsBSig $4) }
 
 -----------------------------------------------------------------------------
 -- Warnings and deprecations (c.f. rules)
@@ -1109,7 +1109,7 @@ tv_bndrs :: { [LHsTyVarBndr RdrName] }
 
 tv_bndr :: { LHsTyVarBndr RdrName }
         : tyvar                         { L1 (UserTyVar (unLoc $1)) }
-        | '(' tyvar '::' kind ')'       { LL (KindedTyVar (unLoc $2) (HsBSig $4 placeHolderBndrs)) }
+        | '(' tyvar '::' kind ')'       { LL (KindedTyVar (unLoc $2) (mkHsBSig $4)) }
 
 fds :: { Located [Located (FunDep RdrName)] }
         : {- empty -}                   { noLoc [] }
diff --git a/compiler/parser/ParserCore.y b/compiler/parser/ParserCore.y
index 70a0e886f1..eee8831065 100644
--- a/compiler/parser/ParserCore.y
+++ b/compiler/parser/ParserCore.y
@@ -377,7 +377,7 @@ ifaceArrow ifT1 ifT2 = IfaceFunTy ifT1 ifT2
 toHsTvBndr :: IfaceTvBndr -> LHsTyVarBndr RdrName
 toHsTvBndr (tv,k) = noLoc $ KindedTyVar (mkRdrUnqual (mkTyVarOccFS tv)) bsig
                   where
-                    bsig = HsBSig (toHsKind k) placeHolderBndrs
+                    bsig = mkHsBSig (toHsKind k)
 
 ifaceExtRdrName :: Name -> RdrName
 ifaceExtRdrName name = mkOrig (nameModule name) (nameOccName name)
diff --git a/compiler/parser/RdrHsSyn.lhs b/compiler/parser/RdrHsSyn.lhs
index 91bab6c3fb..099acd7388 100644
--- a/compiler/parser/RdrHsSyn.lhs
+++ b/compiler/parser/RdrHsSyn.lhs
@@ -5,8 +5,6 @@ Functions over HsSyn specialised to RdrName.
 
 \begin{code}
 module RdrHsSyn (
-        extractHsTyRdrTyVars, extractHsTysRdrTyVars,
-
         mkHsOpApp,
         mkHsIntegral, mkHsFractional, mkHsIsString,
         mkHsDo, mkHsSplice, mkTopSpliceDecl,
@@ -78,11 +76,9 @@ import Bag              ( Bag, emptyBag, consBag )
 import Outputable
 import FastString
 import Maybes
-import Util             ( filterOut )
 import Control.Applicative ((<$>))
 import Control.Monad
 import Text.ParserCombinators.ReadP as ReadP
-import Data.List        ( nub )
 import Data.Char
 
 #include "HsVersions.h"
@@ -91,66 +87,6 @@ import Data.Char
 
 %************************************************************************
 %*                                                                      *
-\subsection{A few functions over HsSyn at RdrName}
-%*                                                                    *
-%************************************************************************
-
-extractHsTyRdrNames finds the free variables of a HsType
-It's used when making the for-alls explicit.
-
-\begin{code}
-extractHsTyRdrTyVars :: LHsType RdrName -> [RdrName]
-extractHsTyRdrTyVars ty = nub (extract_lty ty [])
-
-extractHsTysRdrTyVars :: [LHsType RdrName] -> [RdrName]
-extractHsTysRdrTyVars ty = nub (extract_ltys ty [])
-
-extract_lctxt :: LHsContext RdrName -> [RdrName] -> [RdrName]
-extract_lctxt ctxt acc = foldr extract_lty acc (unLoc ctxt)
-
-extract_ltys :: [LHsType RdrName] -> [RdrName] -> [RdrName]
-extract_ltys tys acc = foldr extract_lty acc tys
-
--- IA0_NOTE: Should this function also return kind variables?
--- (explicit kind poly)
-extract_lty :: LHsType RdrName -> [RdrName] -> [RdrName]
-extract_lty (L _ ty) acc
-  = case ty of
-      HsTyVar tv                -> extract_tv tv acc
-      HsBangTy _ ty             -> extract_lty ty acc
-      HsRecTy flds              -> foldr (extract_lty . cd_fld_type) acc flds
-      HsAppTy ty1 ty2           -> extract_lty ty1 (extract_lty ty2 acc)
-      HsListTy ty               -> extract_lty ty acc
-      HsPArrTy ty               -> extract_lty ty acc
-      HsTupleTy _ tys           -> extract_ltys tys acc
-      HsFunTy ty1 ty2           -> extract_lty ty1 (extract_lty ty2 acc)
-      HsIParamTy _ ty           -> extract_lty ty acc
-      HsEqTy ty1 ty2            -> extract_lty ty1 (extract_lty ty2 acc)
-      HsOpTy ty1 (_, (L _ tv)) ty2 -> extract_tv tv (extract_lty ty1 (extract_lty ty2 acc))
-      HsParTy ty                -> extract_lty ty acc
-      HsCoreTy {}               -> acc  -- The type is closed
-      HsQuasiQuoteTy {}         -> acc  -- Quasi quotes mention no type variables
-      HsSpliceTy {}             -> acc  -- Type splices mention no type variables
-      HsKindSig ty _            -> extract_lty ty acc
-      HsForAllTy _ [] cx ty     -> extract_lctxt cx (extract_lty ty acc)
-      HsForAllTy _ tvs cx ty    -> acc ++ (filterOut (`elem` locals) $
-                                           extract_lctxt cx (extract_lty ty []))
-                                where
-                                   locals = hsLTyVarNames tvs
-      HsDocTy ty _              -> extract_lty ty acc
-      HsExplicitListTy _ tys    -> extract_ltys tys acc
-      HsExplicitTupleTy _ tys   -> extract_ltys tys acc
-      HsTyLit _                 -> acc
-      HsWrapTy _ _              -> panic "extract_lty"
-
-extract_tv :: RdrName -> [RdrName] -> [RdrName]
-extract_tv tv acc | isRdrTyVar tv = tv : acc
-                  | otherwise     = acc
-\end{code}
-
-
-%************************************************************************
-%*                                                                      *
 \subsection{Construction functions for Rdr stuff}
 %*                                                                    *
 %************************************************************************