Merge branch 'master' of darcs.haskell.org:/srv/darcs//ghc

6 files changed, 47 insertions, 13 deletions

diff --git a/compiler/prelude/PrelRules.lhs b/compiler/prelude/PrelRules.lhs
index dab34fc69d..7aeb920e0c 100644
--- a/compiler/prelude/PrelRules.lhs
+++ b/compiler/prelude/PrelRules.lhs
@@ -779,7 +779,11 @@ match_inline _ (Type _ : e : _)
 
 match_inline _ _ = Nothing
 
+-------------------------------------------------
 -- Integer rules
+--   smallInteger  (79::Int#)  = 79::Integer   
+--   wordToInteger (79::Word#) = 79::Integer   
+-- Similarly Int64, Word64
 
 match_IntToInteger :: Id
                    -> IdUnfoldingFun
@@ -833,6 +837,7 @@ match_Word64ToInteger id id_unf [xl]
         panic "match_Word64ToInteger: Id has the wrong type"
 match_Word64ToInteger _ _ _ = Nothing
 
+-------------------------------------------------
 match_Integer_convert :: Num a
                       => (a -> Expr CoreBndr)
                       -> Id
diff --git a/compiler/typecheck/TcHsType.lhs b/compiler/typecheck/TcHsType.lhs
index 1e30d7c328..8b4004490b 100644
--- a/compiler/typecheck/TcHsType.lhs
+++ b/compiler/typecheck/TcHsType.lhs
@@ -850,6 +850,7 @@ tcHsTyVarBndr :: LHsTyVarBndr Name -> TcM TyVar
 --   instance C (a,b) where
 --     type F (a,b) c = ...
 -- Here a,b will be in scope when processing the associated type instance for F.
+-- See Note [Associated type tyvar names] in TyCon
 tcHsTyVarBndr (L _ hs_tv)
   = do { let name = hsTyVarName hs_tv
        ; mb_tv <- tcLookupLcl_maybe name
diff --git a/compiler/typecheck/TcRnMonad.lhs b/compiler/typecheck/TcRnMonad.lhs
index f68599898e..1b60061675 100644
--- a/compiler/typecheck/TcRnMonad.lhs
+++ b/compiler/typecheck/TcRnMonad.lhs
@@ -1031,11 +1031,6 @@ emitImplication ct
   = do { lie_var <- getConstraintVar ;
          updTcRef lie_var (`addImplics` unitBag ct) }
 
-emitWC :: WantedConstraints -> TcM ()
-emitWC wc
-  = do { emitFlats (keepWanted (wc_flat wc))
-       ; emitImplications (wc_impl wc) }
-
 emitImplications :: Bag Implication -> TcM ()
 emitImplications ct
   = do { lie_var <- getConstraintVar ;
diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 2c4d318335..4417408100 100644
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -416,9 +416,10 @@ simplifyInfer _top_lvl apply_mr name_taus (untch,wanteds)
              
 
        ; if isEmptyVarSet qtvs && isEmptyBag bound
-         then ASSERT( isEmptyBag (wc_insol wanted_transformed) )
-              do { traceTc "} simplifyInfer/no quantification" empty                   
-                 ; emitWC wanted_transformed
+         then do { traceTc "} simplifyInfer/no quantification" empty                   
+                 ; emitConstraints wanted_transformed
+                    -- Includes insolubles (if -fdefer-type-errors)
+                    -- as well as flats and implications
                  ; return ([], [], mr_bites, TcEvBinds ev_binds_var) }
          else do
 
diff --git a/compiler/typecheck/TcTyClsDecls.lhs b/compiler/typecheck/TcTyClsDecls.lhs
index ab2880488d..2872f46a3e 100644
--- a/compiler/typecheck/TcTyClsDecls.lhs
+++ b/compiler/typecheck/TcTyClsDecls.lhs
@@ -1484,14 +1484,29 @@ checkValidClass cls
            ; tcAddDefaultAssocDeclCtxt (tyConName fam_tc) $ 
              mapM_ (check_loc_at_def fam_tc) defs }
 
+    -- Check that the index of the type instance is the same as on
+    -- its parent class.  Eg
+    --    class C a b where
+    --       type F b x a ::*
+    --    instnace C Int Bool where
+    --       type F Bool Char Int = Int
+    --       type F Bool Bool Int = Bool
+    --  Here the first and third args should match
+    --  the (C Int Bool)  header
+    -- This is not to do with soundness; it's just checking that the
+    -- type instance arg is the sam
     check_loc_at_def fam_tc (ATD _tvs pats _rhs loc)
       -- Set the location for each of the default declarations
       = setSrcSpan loc $ zipWithM_ check_arg (tyConTyVars fam_tc) pats
 
     -- We only want to check this on the *class* TyVars,
     -- not the *family* TyVars (there may be more of these)
+    -- Nor do we want to check kind vars, for which we don't enforce
+    -- the "same name as parent" rule as we do for type variables
+    -- c.f. Trac #7073
     check_arg fam_tc_tv at_ty
-      = checkTc (   not (fam_tc_tv `elem` tyvars)
+      = checkTc (   isKindVar fam_tc_tv
+                 || not (fam_tc_tv `elem` tyvars)
                  || mkTyVarTy fam_tc_tv `eqType` at_ty) 
           (wrongATArgErr at_ty (mkTyVarTy fam_tc_tv))
 
diff --git a/compiler/types/Class.lhs b/compiler/types/Class.lhs
index 136ecec81a..c70f16dbc6 100644
--- a/compiler/types/Class.lhs
+++ b/compiler/types/Class.lhs
@@ -96,10 +96,8 @@ data DefMeth = NoDefMeth 		-- No default method
 	     | GenDefMeth Name 		-- A generic default method
              deriving Eq
 
-type ClassATItem = (TyCon, [ATDefault])
-  -- Default associated types from these templates. If the template list is empty,
-  -- we assume that there is no default -- not that the default is to generate no
-  -- instances (this only makes a difference for warnings).
+type ClassATItem = (TyCon,           -- See Note [Associated type tyvar names]
+                    [ATDefault])     -- Default associated types from these templates 
   -- We can have more than one default per type; see
   -- Note [Associated type defaults] in TcTyClsDecls
 
@@ -149,6 +147,25 @@ mkClass tyvars fds super_classes superdict_sels at_stuff
 		classTyCon   = tycon }
 \end{code}
 
+Note [Associated type tyvar names]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The TyCon of an associated type should use the same variable names as its
+parent class. Thus
+    class C a b where
+      type F b x a :: *
+We make F use the same Name for 'a' as C does, and similary 'b'.
+
+The only reason for this is when checking instances it's easier to match 
+them up, to ensure they match.  Eg
+    instance C Int [d] where
+      type F [d] x Int = ....
+we should make sure that the first and third args match the instance
+header.
+
+This is the reason we use the Name and TyVar from the parent declaration,
+in both class and instance decls: just to make this check easier.
+
+
 %************************************************************************
 %*									*
 \subsection[Class-selectors]{@Class@: simple selectors}