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.

1 files changed, 1 insertions, 1 deletions

diff --git a/utils/ghctags/Main.hs b/utils/ghctags/Main.hs
index 118bcac0be..a25537ee99 100644
--- a/utils/ghctags/Main.hs
+++ b/utils/ghctags/Main.hs
@@ -251,7 +251,7 @@ boundValues mod group =
                        , bind <- bagToList binds
                        , x <- boundThings mod bind ]
                _other -> error "boundValues"
-      tys = [ n | ns <- map hsTyClDeclBinders (hs_tyclds group)
+      tys = [ n | ns <- map hsTyClDeclBinders (concat (hs_tyclds group))
                 , n <- map found ns ]
       fors = concat $ map forBound (hs_fords group)
              where forBound lford = case unLoc lford of