Do dependency analysis when kind-checking type declarations

This patch fixes Trac #4875.  The main point is to do dependency
analysis on type and class declarations, and kind-check them in
dependency order, so as to improve error messages.

This patch means that a few programs that would typecheck before won't
typecheck any more; but before we were (naughtily) going beyond
Haskell 98 without any language-extension flags, and Trac #4875
convinces me that doing so is a Bad Idea.

Here's an example that won't typecheck any more
       data T a b = MkT (a b)
       type F k = T k Maybe

If you look at T on its own you'd default 'a' to kind *->*;
and then kind-checking would fail on F.

But GHC currently accepts this program beause it looks at
the *occurrences* of T.

2 files changed, 12 insertions, 5 deletions

diff --git a/compiler/hsSyn/HsDecls.lhs b/compiler/hsSyn/HsDecls.lhs
index fd6d3bbf45..8827f3ab64 100644
--- a/compiler/hsSyn/HsDecls.lhs
+++ b/compiler/hsSyn/HsDecls.lhs
@@ -126,7 +126,12 @@ data HsDecl id
 data HsGroup id
   = HsGroup {
 	hs_valds  :: HsValBinds id,
-	hs_tyclds :: [LTyClDecl id],
+
+	hs_tyclds :: [[LTyClDecl id]],	
+		-- A list of mutually-recursive groups
+		-- Parser generates a singleton list;
+		-- renamer does dependency analysis
+
 	hs_instds :: [LInstDecl id],
         hs_derivds :: [LDerivDecl id],
 
@@ -228,7 +233,8 @@ instance OutputableBndr name => Outputable (HsGroup name) where
 	     if isEmptyValBinds val_decls 
                 then Nothing 
                 else Just (ppr val_decls),
-	     ppr_ds tycl_decls, ppr_ds inst_decls,
+	     ppr_ds (concat tycl_decls), 
+             ppr_ds inst_decls,
              ppr_ds deriv_decls,
 	     ppr_ds foreign_decls]
 	where
diff --git a/compiler/hsSyn/HsUtils.lhs b/compiler/hsSyn/HsUtils.lhs
index d17f85099f..3ef4bff177 100644
--- a/compiler/hsSyn/HsUtils.lhs
+++ b/compiler/hsSyn/HsUtils.lhs
@@ -60,7 +60,7 @@ module HsUtils(
   collectLStmtBinders, collectStmtBinders,
   collectSigTysFromPats, collectSigTysFromPat,
 
-  hsTyClDeclBinders, hsTyClDeclsBinders, hsConDeclsBinders, 
+  hsTyClDeclBinders, hsTyClDeclsBinders, 
   hsForeignDeclsBinders, hsGroupBinders
   ) where
 
@@ -572,9 +572,10 @@ hsForeignDeclsBinders :: [LForeignDecl Name] -> [Name]
 hsForeignDeclsBinders foreign_decls
   = [n | L _ (ForeignImport (L _ n) _ _) <- foreign_decls]
 
-hsTyClDeclsBinders :: [Located (TyClDecl Name)] -> [Located (InstDecl Name)] -> [Name]
+hsTyClDeclsBinders :: [[LTyClDecl Name]] -> [Located (InstDecl Name)] -> [Name]
 hsTyClDeclsBinders tycl_decls inst_decls
-  = [n | d <- instDeclATs inst_decls ++ tycl_decls, L _ n <- hsTyClDeclBinders d]
+  = [n | d <- instDeclATs inst_decls ++ concat tycl_decls
+       , L _ n <- hsTyClDeclBinders d]
 
 hsTyClDeclBinders :: Eq name => Located (TyClDecl name) -> [Located name]
 -- ^ Returns all the /binding/ names of the decl, along with their SrcLocs.