{-# OPTIONS -fno-warn-tabs #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and
-- detab the module (please do the detabbing in a separate patch). See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces
-- for details

module RnBinds (
   -- Renaming top-level bindings
   rnTopBindsLHS, rnTopBindsRHS, rnValBindsRHS,

   -- Renaming local bindings
   rnLocalBindsAndThen, rnLocalValBindsLHS, rnLocalValBindsRHS,

   -- Other bindings
   rnMethodBinds, renameSigs, mkSigTvFn,
   rnMatchGroup, rnGRHSs, rnGRHS,
   makeMiniFixityEnv, MiniFixityEnv,
   HsSigCtxt(..)
   ) where

import {-# SOURCE #-} RnExpr( rnLExpr, rnStmts )

import HsSyn
import TcRnMonad
import TcEvidence     ( emptyTcEvBinds )
import RnTypes        ( bindSigTyVarsFV, rnHsSigType, rnLHsType, checkPrecMatch )
import RnPat
import RnEnv
import DynFlags
import Module
import Name
import NameEnv
import NameSet
import RdrName          ( RdrName, rdrNameOcc )
import SrcLoc
import ListSetOps	( findDupsEq )
import BasicTypes	( RecFlag(..) )
import Digraph		( SCC(..) )
import Bag
import Outputable
import FastString
import Data.List	( partition, sort )
import Maybes		( orElse )
import Control.Monad

-- for top-level bindings, we need to make top-level names,
-- so we have a different entry point than for local bindings
rnTopBindsLHS :: MiniFixityEnv
              -> HsValBinds RdrName 
              -> RnM (HsValBindsLR Name RdrName)
rnTopBindsLHS fix_env binds
  = rnValBindsLHS (topRecNameMaker fix_env) binds

rnTopBindsRHS :: NameSet -> HsValBindsLR Name RdrName 
              -> RnM (HsValBinds Name, DefUses)
rnTopBindsRHS bound_names binds
  = do { is_boot <- tcIsHsBoot
       ; if is_boot 
         then rnTopBindsBoot binds
         else rnValBindsRHS (TopSigCtxt bound_names False) binds }

rnTopBindsBoot :: HsValBindsLR Name RdrName -> RnM (HsValBinds Name, DefUses)
-- A hs-boot file has no bindings. 
-- Return a single HsBindGroup with empty binds and renamed signatures
rnTopBindsBoot (ValBindsIn mbinds sigs)
  = do	{ checkErr (isEmptyLHsBinds mbinds) (bindsInHsBootFile mbinds)
	; (sigs', fvs) <- renameSigs HsBootCtxt sigs
	; return (ValBindsOut [] sigs', usesOnly fvs) }
rnTopBindsBoot b = pprPanic "rnTopBindsBoot" (ppr b)

rnLocalBindsAndThen :: HsLocalBinds RdrName
                    -> (HsLocalBinds Name -> RnM (result, FreeVars))
                    -> RnM (result, FreeVars)
-- This version (a) assumes that the binding vars are *not* already in scope
--		 (b) removes the binders from the free vars of the thing inside
-- The parser doesn't produce ThenBinds
rnLocalBindsAndThen EmptyLocalBinds thing_inside
  = thing_inside EmptyLocalBinds

rnLocalBindsAndThen (HsValBinds val_binds) thing_inside
  = rnLocalValBindsAndThen val_binds $ \ val_binds' -> 
      thing_inside (HsValBinds val_binds')

rnLocalBindsAndThen (HsIPBinds binds) thing_inside = do
    (binds',fv_binds) <- rnIPBinds binds
    (thing, fvs_thing) <- thing_inside (HsIPBinds binds')
    return (thing, fvs_thing `plusFV` fv_binds)

rnIPBinds :: HsIPBinds RdrName -> RnM (HsIPBinds Name, FreeVars)
rnIPBinds (IPBinds ip_binds _no_dict_binds) = do
    (ip_binds', fvs_s) <- mapAndUnzipM (wrapLocFstM rnIPBind) ip_binds
    return (IPBinds ip_binds' emptyTcEvBinds, plusFVs fvs_s)

rnIPBind :: IPBind RdrName -> RnM (IPBind Name, FreeVars)
rnIPBind (IPBind ~(Left n) expr) = do
    (expr',fvExpr) <- rnLExpr expr
    return (IPBind (Left n) expr', fvExpr)

-- Renaming local binding gropus 
-- Does duplicate/shadow check
rnLocalValBindsLHS :: MiniFixityEnv
                   -> HsValBinds RdrName
                   -> RnM ([Name], HsValBindsLR Name RdrName)
rnLocalValBindsLHS fix_env binds 
  = do { binds' <- rnValBindsLHS (localRecNameMaker fix_env) binds 

         -- Check for duplicates and shadowing
	 -- Must do this *after* renaming the patterns
	 -- See Note [Collect binders only after renaming] in HsUtils

         -- We need to check for dups here because we
     	 -- don't don't bind all of the variables from the ValBinds at once
     	 -- with bindLocatedLocals any more.
         -- 
     	 -- Note that we don't want to do this at the top level, since
     	 -- sorting out duplicates and shadowing there happens elsewhere.
     	 -- The behavior is even different. For example,
     	 --   import A(f)
     	 --   f = ...
     	 -- should not produce a shadowing warning (but it will produce
     	 -- an ambiguity warning if you use f), but
     	 --   import A(f)
     	 --   g = let f = ... in f
     	 -- should.
       ; let bound_names = collectHsValBinders binds'
       ; envs <- getRdrEnvs
       ; checkDupAndShadowedNames envs bound_names

       ; return (bound_names, binds') }

-- renames the left-hand sides
-- generic version used both at the top level and for local binds
-- does some error checking, but not what gets done elsewhere at the top level
rnValBindsLHS :: NameMaker 
              -> HsValBinds RdrName
              -> RnM (HsValBindsLR Name RdrName)
rnValBindsLHS topP (ValBindsIn mbinds sigs)
  = do { mbinds' <- mapBagM (rnBindLHS topP doc) mbinds
       ; return $ ValBindsIn mbinds' sigs }
  where
    bndrs = collectHsBindsBinders mbinds
    doc   = text "In the binding group for:" <+> pprWithCommas ppr bndrs

rnValBindsLHS _ b = pprPanic "rnValBindsLHSFromDoc" (ppr b)

-- General version used both from the top-level and for local things
-- Assumes the LHS vars are in scope
--
-- Does not bind the local fixity declarations
rnValBindsRHS :: HsSigCtxt 
              -> HsValBindsLR Name RdrName
              -> RnM (HsValBinds Name, DefUses)

rnValBindsRHS ctxt (ValBindsIn mbinds sigs)
  = do { (sigs', sig_fvs) <- renameSigs ctxt sigs
       ; binds_w_dus <- mapBagM (rnBind (mkSigTvFn sigs')) mbinds
       ; case depAnalBinds binds_w_dus of
           (anal_binds, anal_dus) -> return (valbind', valbind'_dus)
              where
                valbind' = ValBindsOut anal_binds sigs'
                valbind'_dus = anal_dus `plusDU` usesOnly sig_fvs
			       -- Put the sig uses *after* the bindings
			       -- so that the binders are removed from 
			       -- the uses in the sigs
       }

rnValBindsRHS _ b = pprPanic "rnValBindsRHS" (ppr b)

-- Wrapper for local binds
--
-- The *client* of this function is responsible for checking for unused binders;
-- it doesn't (and can't: we don't have the thing inside the binds) happen here
--
-- The client is also responsible for bringing the fixities into scope
rnLocalValBindsRHS :: NameSet  -- names bound by the LHSes
                   -> HsValBindsLR Name RdrName
                   -> RnM (HsValBinds Name, DefUses)
rnLocalValBindsRHS bound_names binds
  = rnValBindsRHS (LocalBindCtxt bound_names) binds

-- for local binds
-- wrapper that does both the left- and right-hand sides 
--
-- here there are no local fixity decls passed in;
-- the local fixity decls come from the ValBinds sigs
rnLocalValBindsAndThen :: HsValBinds RdrName
                       -> (HsValBinds Name -> RnM (result, FreeVars))
                       -> RnM (result, FreeVars)
rnLocalValBindsAndThen binds@(ValBindsIn _ sigs) thing_inside
 = do	{     -- (A) Create the local fixity environment 
	  new_fixities <- makeMiniFixityEnv [L loc sig | L loc (FixSig sig) <- sigs]

	      -- (B) Rename the LHSes 
	; (bound_names, new_lhs) <- rnLocalValBindsLHS new_fixities binds

	      --     ...and bring them (and their fixities) into scope
	; bindLocalNamesFV bound_names              $
          addLocalFixities new_fixities bound_names $ do

	{      -- (C) Do the RHS and thing inside
	  (binds', dus) <- rnLocalValBindsRHS (mkNameSet bound_names) new_lhs 
        ; (result, result_fvs) <- thing_inside binds'

		-- Report unused bindings based on the (accurate) 
		-- findUses.  E.g.
		-- 	let x = x in 3
		-- should report 'x' unused
	; let real_uses = findUses dus result_fvs
	      -- Insert fake uses for variables introduced implicitly by wildcards (#4404)
	      implicit_uses = hsValBindsImplicits binds'
	; warnUnusedLocalBinds bound_names (real_uses `unionNameSets` implicit_uses)

	; let
            -- The variables "used" in the val binds are: 
            --   (1) the uses of the binds (allUses)
            --   (2) the FVs of the thing-inside
            all_uses = allUses dus `plusFV` result_fvs
		-- Note [Unused binding hack]
		-- ~~~~~~~~~~~~~~~~~~~~~~~~~~
		-- Note that *in contrast* to the above reporting of
		-- unused bindings, (1) above uses duUses to return *all* 
		-- the uses, even if the binding is unused.  Otherwise consider:
                --	x = 3
                --	y = let p = x in 'x'	-- NB: p not used
                -- If we don't "see" the dependency of 'y' on 'x', we may put the
                -- bindings in the wrong order, and the type checker will complain
                -- that x isn't in scope
		--
		-- But note that this means we won't report 'x' as unused, 
		-- whereas we would if we had { x = 3; p = x; y = 'x' }

	; return (result, all_uses) }}
         	-- The bound names are pruned out of all_uses
	        -- by the bindLocalNamesFV call above

rnLocalValBindsAndThen bs _ = pprPanic "rnLocalValBindsAndThen" (ppr bs)


-- Process the fixity declarations, making a FastString -> (Located Fixity) map
-- (We keep the location around for reporting duplicate fixity declarations.)
-- 
-- Checks for duplicates, but not that only locally defined things are fixed.
-- Note: for local fixity declarations, duplicates would also be checked in
--       check_sigs below.  But we also use this function at the top level.

makeMiniFixityEnv :: [LFixitySig RdrName] -> RnM MiniFixityEnv

makeMiniFixityEnv decls = foldlM add_one emptyFsEnv decls
 where
   add_one env (L loc (FixitySig (L name_loc name) fixity)) = do
     { -- this fixity decl is a duplicate iff
       -- the ReaderName's OccName's FastString is already in the env
       -- (we only need to check the local fix_env because
       --  definitions of non-local will be caught elsewhere)
       let { fs = occNameFS (rdrNameOcc name)
           ; fix_item = L loc fixity };

       case lookupFsEnv env fs of
         Nothing -> return $ extendFsEnv env fs fix_item
         Just (L loc' _) -> do
           { setSrcSpan loc $ 
             addErrAt name_loc (dupFixityDecl loc' name)
           ; return env}
     }

dupFixityDecl :: SrcSpan -> RdrName -> SDoc
dupFixityDecl loc rdr_name
  = vcat [ptext (sLit "Multiple fixity declarations for") <+> quotes (ppr rdr_name),
	  ptext (sLit "also at ") <+> ppr loc]

---------------------

-- renaming a single bind

rnBindLHS :: NameMaker
          -> SDoc 
          -> LHsBind RdrName
          -- returns the renamed left-hand side,
          -- and the FreeVars *of the LHS*
          -- (i.e., any free variables of the pattern)
          -> RnM (LHsBindLR Name RdrName)

rnBindLHS name_maker _ (L loc bind@(PatBind { pat_lhs = pat }))
  = setSrcSpan loc $ do
      -- we don't actually use the FV processing of rnPatsAndThen here
      (pat',pat'_fvs) <- rnBindPat name_maker pat
      return (L loc (bind { pat_lhs = pat', bind_fvs = pat'_fvs }))
                -- We temporarily store the pat's FVs in bind_fvs;
                -- gets updated to the FVs of the whole bind
                -- when doing the RHS below
                            
rnBindLHS name_maker _ (L loc bind@(FunBind { fun_id = name@(L nameLoc _) }))
  = setSrcSpan loc $ 
    do { newname <- applyNameMaker name_maker name
       ; return (L loc (bind { fun_id = L nameLoc newname })) } 

rnBindLHS _ _ b = pprPanic "rnBindLHS" (ppr b)

-- assumes the left-hands-side vars are in scope
rnBind :: (Name -> [Name])		-- Signature tyvar function
       -> LHsBindLR Name RdrName
       -> RnM (LHsBind Name, [Name], Uses)
rnBind _ (L loc bind@(PatBind { pat_lhs = pat
                              , pat_rhs = grhss 
                                      -- pat fvs were stored in bind_fvs
                                      -- after processing the LHS
                              , bind_fvs = pat_fvs }))
  = setSrcSpan loc $ 
    do	{ mod <- getModule
        ; (grhss', rhs_fvs) <- rnGRHSs PatBindRhs rnLExpr grhss

		-- No scoped type variables for pattern bindings
	; let all_fvs = pat_fvs `plusFV` rhs_fvs
              fvs'    = filterNameSet (nameIsLocalOrFrom mod) all_fvs
	        -- Keep locally-defined Names
		-- As well as dependency analysis, we need these for the
		-- MonoLocalBinds test in TcBinds.decideGeneralisationPlan
              bndrs = collectPatBinders pat
              bind' = bind { pat_rhs  = grhss', bind_fvs = fvs' }
              is_wild_pat = case pat of
                              L _ (WildPat {}) -> True
                              _                -> False

        -- Warn if the pattern binds no variables, except for the
        -- entirely-explicit idiom    _ = rhs
        -- which (a) is not that different from  _v = rhs
        --       (b) is sometimes used to give a type sig for,
        --           or an occurrence of, a variable on the RHS
        ; whenWOptM Opt_WarnUnusedBinds $
          when (null bndrs && not is_wild_pat) $
          addWarn $ unusedPatBindWarn bind'

	; fvs' `seq` -- See Note [Free-variable space leak]
          return (L loc bind', bndrs, all_fvs) }

rnBind sig_fn (L loc bind@(FunBind { fun_id = name 
                            	   , fun_infix = is_infix 
                            	   , fun_matches = matches })) 
       -- invariant: no free vars here when it's a FunBind
  = setSrcSpan loc $
    do	{ let plain_name = unLoc name

	; (matches', rhs_fvs) <- bindSigTyVarsFV (sig_fn plain_name) $
				-- bindSigTyVars tests for Opt_ScopedTyVars
			         rnMatchGroup (FunRhs plain_name is_infix) rnLExpr matches
	; when is_infix $ checkPrecMatch plain_name matches'

        ; mod <- getModule
        ; let fvs' = filterNameSet (nameIsLocalOrFrom mod) rhs_fvs
	        -- Keep locally-defined Names
		-- As well as dependency analysis, we need these for the
		-- MonoLocalBinds test in TcBinds.decideGeneralisationPlan

	; fvs' `seq` -- See Note [Free-variable space leak]
          return (L loc (bind { fun_matches = matches'
			      , bind_fvs   = fvs' }), 
		  [plain_name], rhs_fvs)
      }

rnBind _ b = pprPanic "rnBind" (ppr b)

{-
Note [Free-variable space leak]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We have
    fvs' = trim fvs
and we seq fvs' before turning it as part of a record.

The reason is that trim is sometimes something like
    \xs -> intersectNameSet (mkNameSet bound_names) xs
and we don't want to retain the list bound_names. This showed up in
trac ticket #1136.
-}

---------------------
depAnalBinds :: Bag (LHsBind Name, [Name], Uses)
	     -> ([(RecFlag, LHsBinds Name)], DefUses)
-- Dependency analysis; this is important so that 
-- unused-binding reporting is accurate
depAnalBinds binds_w_dus
  = (map get_binds sccs, map get_du sccs)
  where
    sccs = depAnal (\(_, defs, _) -> defs)
                   (\(_, _, uses) -> nameSetToList uses)
                   (bagToList binds_w_dus)

    get_binds (AcyclicSCC (bind, _, _)) = (NonRecursive, unitBag bind)
    get_binds (CyclicSCC  binds_w_dus)  = (Recursive, listToBag [b | (b,_,_) <- binds_w_dus])

    get_du (AcyclicSCC (_, bndrs, uses)) = (Just (mkNameSet bndrs), uses)
    get_du (CyclicSCC  binds_w_dus)      = (Just defs, uses)
	where
	  defs = mkNameSet [b | (_,bs,_) <- binds_w_dus, b <- bs]
	  uses = unionManyNameSets [u | (_,_,u) <- binds_w_dus]

---------------------
-- Bind the top-level forall'd type variables in the sigs.
-- E.g 	f :: a -> a
--	f = rhs
--	The 'a' scopes over the rhs
--
-- NB: there'll usually be just one (for a function binding)
--     but if there are many, one may shadow the rest; too bad!
--	e.g  x :: [a] -> [a]
--	     y :: [(a,a)] -> a
--	     (x,y) = e
--      In e, 'a' will be in scope, and it'll be the one from 'y'!

mkSigTvFn :: [LSig Name] -> (Name -> [Name])
-- Return a lookup function that maps an Id Name to the names
-- of the type variables that should scope over its body..
mkSigTvFn sigs
  = \n -> lookupNameEnv env n `orElse` []
  where
    env :: NameEnv [Name]
    env = mkNameEnv [ (name, hsLKiTyVarNames ltvs)  -- Kind variables and type variables
		    | L _ (TypeSig names
			           (L _ (HsForAllTy Explicit ltvs _ _))) <- sigs
                    , (L _ name) <- names]
	-- Note the pattern-match on "Explicit"; we only bind
	-- type variables from signatures with an explicit top-level for-all

rnMethodBinds :: Name			-- Class name
	      -> (Name -> [Name])	-- Signature tyvar function
	      -> LHsBinds RdrName
	      -> RnM (LHsBinds Name, FreeVars)

rnMethodBinds cls sig_fn binds
  = do { checkDupRdrNames meth_names
	     -- Check that the same method is not given twice in the
	     -- same instance decl	instance C T where
	     --			      f x = ...
	     --			      g y = ...
	     --			      f x = ...
	     -- We must use checkDupRdrNames because the Name of the
	     -- method is the Name of the class selector, whose SrcSpan
	     -- points to the class declaration; and we use rnMethodBinds
	     -- for instance decls too

       ; foldlM do_one (emptyBag, emptyFVs) (bagToList binds) }
  where 
    meth_names  = collectMethodBinders binds
    do_one (binds,fvs) bind 
       = do { (bind', fvs_bind) <- rnMethodBind cls sig_fn bind
	    ; return (binds `unionBags` bind', fvs_bind `plusFV` fvs) }

rnMethodBind :: Name
	      -> (Name -> [Name])
	      -> LHsBindLR RdrName RdrName
	      -> RnM (Bag (LHsBindLR Name Name), FreeVars)
rnMethodBind cls sig_fn 
             (L loc bind@(FunBind { fun_id = name, fun_infix = is_infix 
				  , fun_matches = MG { mg_alts = matches } }))
  = setSrcSpan loc $ do
    sel_name <- wrapLocM (lookupInstDeclBndr cls (ptext (sLit "method"))) name
    let plain_name = unLoc sel_name
        -- We use the selector name as the binder

    (new_matches, fvs) <- bindSigTyVarsFV (sig_fn plain_name) $
                          mapFvRn (rnMatch (FunRhs plain_name is_infix) rnLExpr) matches
    let new_group = mkMatchGroup new_matches

    when is_infix $ checkPrecMatch plain_name new_group
    return (unitBag (L loc (bind { fun_id      = sel_name 
                                 , fun_matches = new_group
                                 , bind_fvs    = fvs })),
             fvs `addOneFV` plain_name)
        -- The 'fvs' field isn't used for method binds

-- Can't handle method pattern-bindings which bind multiple methods.
rnMethodBind _ _ (L loc bind@(PatBind {})) = do
    addErrAt loc (methodBindErr bind)
    return (emptyBag, emptyFVs)

rnMethodBind _ _ b = pprPanic "rnMethodBind" (ppr b)

renameSigs :: HsSigCtxt 
	   -> [LSig RdrName]
	   -> RnM ([LSig Name], FreeVars)
-- Renames the signatures and performs error checks
renameSigs ctxt sigs 
  = do	{ mapM_ dupSigDeclErr (findDupSigs sigs)
		
	; (sigs', sig_fvs) <- mapFvRn (wrapLocFstM (renameSig ctxt)) sigs

	; let (good_sigs, bad_sigs) = partition (okHsSig ctxt) sigs'
	; mapM_ misplacedSigErr bad_sigs		 -- Misplaced

	; return (good_sigs, sig_fvs) } 

----------------------
-- We use lookupSigOccRn in the signatures, which is a little bit unsatisfactory
-- because this won't work for:
--	instance Foo T where
--	  {-# INLINE op #-}
--	  Baz.op = ...
-- We'll just rename the INLINE prag to refer to whatever other 'op'
-- is in scope.  (I'm assuming that Baz.op isn't in scope unqualified.)
-- Doesn't seem worth much trouble to sort this.

renameSig :: HsSigCtxt -> Sig RdrName -> RnM (Sig Name, FreeVars)
-- FixitySig is renamed elsewhere.
renameSig _ (IdSig x)
  = return (IdSig x, emptyFVs)	  -- Actually this never occurs

renameSig ctxt sig@(TypeSig vs ty)
  = do	{ new_vs <- mapM (lookupSigOccRn ctxt sig) vs
	; (new_ty, fvs) <- rnHsSigType (ppr_sig_bndrs vs) ty
	; return (TypeSig new_vs new_ty, fvs) }

renameSig ctxt sig@(GenericSig vs ty)
  = do	{ defaultSigs_on <- xoptM Opt_DefaultSignatures
        ; unless defaultSigs_on (addErr (defaultSigErr sig))
        ; new_v <- mapM (lookupSigOccRn ctxt sig) vs
	; (new_ty, fvs) <- rnHsSigType (ppr_sig_bndrs vs) ty
	; return (GenericSig new_v new_ty, fvs) }

renameSig _ (SpecInstSig ty)
  = do	{ (new_ty, fvs) <- rnLHsType SpecInstSigCtx ty
	; return (SpecInstSig new_ty,fvs) }

-- {-# SPECIALISE #-} pragmas can refer to imported Ids
-- so, in the top-level case (when mb_names is Nothing)
-- we use lookupOccRn.  If there's both an imported and a local 'f'
-- then the SPECIALISE pragma is ambiguous, unlike all other signatures
renameSig ctxt sig@(SpecSig v ty inl)
  = do	{ new_v <- case ctxt of 
                     TopSigCtxt {} -> lookupLocatedOccRn v
                     _             -> lookupSigOccRn ctxt sig v
	; (new_ty, fvs) <- rnHsSigType (quotes (ppr v)) ty
	; return (SpecSig new_v new_ty inl, fvs) }

renameSig ctxt sig@(InlineSig v s)
  = do	{ new_v <- lookupSigOccRn ctxt sig v
	; return (InlineSig new_v s, emptyFVs) }

renameSig ctxt sig@(FixSig (FixitySig v f))
  = do	{ new_v <- lookupSigOccRn ctxt sig v
	; return (FixSig (FixitySig new_v f), emptyFVs) }

ppr_sig_bndrs :: [Located RdrName] -> SDoc
ppr_sig_bndrs bs = quotes (pprWithCommas ppr bs)

okHsSig :: HsSigCtxt -> LSig a -> Bool
okHsSig ctxt (L _ sig) 
  = case (sig, ctxt) of
     (GenericSig {}, ClsDeclCtxt {}) -> True
     (GenericSig {}, _)              -> False

     (TypeSig {}, _)              -> True

     (FixSig {}, InstDeclCtxt {}) -> False
     (FixSig {}, _)               -> True

     (IdSig {}, TopSigCtxt {})   -> True
     (IdSig {}, InstDeclCtxt {}) -> True
     (IdSig {}, _)               -> False

     (InlineSig {}, HsBootCtxt) -> False
     (InlineSig {}, _)          -> True

     (SpecSig {}, TopSigCtxt {})    -> True
     (SpecSig {}, LocalBindCtxt {}) -> True
     (SpecSig {}, InstDeclCtxt {})  -> True
     (SpecSig {}, _)                -> False

     (SpecInstSig {}, InstDeclCtxt {}) -> True
     (SpecInstSig {}, _)               -> False

-------------------
findDupSigs :: [LSig RdrName] -> [[(Located RdrName, Sig RdrName)]]
-- Check for duplicates on RdrName version, 
-- because renamed version has unboundName for
-- not-in-scope binders, which gives bogus dup-sig errors
-- NB: in a class decl, a 'generic' sig is not considered 
--     equal to an ordinary sig, so we allow, say
--     	     class C a where
--	       op :: a -> a
--             default op :: Eq a => a -> a
findDupSigs sigs
  = findDupsEq matching_sig (concatMap (expand_sig . unLoc) sigs)
  where
    expand_sig sig@(FixSig (FixitySig n _)) = [(n,sig)]
    expand_sig sig@(InlineSig n _)          = [(n,sig)]
    expand_sig sig@(TypeSig  ns _)   = [(n,sig) | n <- ns]
    expand_sig sig@(GenericSig ns _) = [(n,sig) | n <- ns]
    expand_sig _ = []

    matching_sig (L _ n1,sig1) (L _ n2,sig2) = n1 == n2 && mtch sig1 sig2
    mtch (FixSig {})     (FixSig {})     = True
    mtch (InlineSig {})  (InlineSig {})  = True
    mtch (TypeSig {})    (TypeSig {})    = True
    mtch (GenericSig {}) (GenericSig {}) = True
    mtch _ _ = False

rnMatchGroup :: Outputable (body RdrName) => HsMatchContext Name
             -> (Located (body RdrName) -> RnM (Located (body Name), FreeVars))
             -> MatchGroup RdrName (Located (body RdrName))
             -> RnM (MatchGroup Name (Located (body Name)), FreeVars)
rnMatchGroup ctxt rnBody (MG { mg_alts = ms }) 
  = do { empty_case_ok <- xoptM Opt_EmptyCase
       ; when (null ms && not empty_case_ok) (addErr (emptyCaseErr ctxt))
       ; (new_ms, ms_fvs) <- mapFvRn (rnMatch ctxt rnBody) ms
       ; return (mkMatchGroup new_ms, ms_fvs) }

rnMatch :: Outputable (body RdrName) => HsMatchContext Name
        -> (Located (body RdrName) -> RnM (Located (body Name), FreeVars))
        -> LMatch RdrName (Located (body RdrName))
        -> RnM (LMatch Name (Located (body Name)), FreeVars)
rnMatch ctxt rnBody = wrapLocFstM (rnMatch' ctxt rnBody)

rnMatch' :: Outputable (body RdrName) => HsMatchContext Name 
         -> (Located (body RdrName) -> RnM (Located (body Name), FreeVars))
         -> Match RdrName (Located (body RdrName))
         -> RnM (Match Name (Located (body Name)), FreeVars)
rnMatch' ctxt rnBody match@(Match pats maybe_rhs_sig grhss)
  = do 	{ 	-- Result type signatures are no longer supported
	  case maybe_rhs_sig of	
	        Nothing -> return ()
	        Just (L loc ty) -> addErrAt loc (resSigErr ctxt match ty)

	       -- Now the main event
	       -- note that there are no local ficity decls for matches
	; rnPats ctxt pats	$ \ pats' -> do
	{ (grhss', grhss_fvs) <- rnGRHSs ctxt rnBody grhss

	; return (Match pats' Nothing grhss', grhss_fvs) }}

emptyCaseErr :: HsMatchContext Name -> SDoc
emptyCaseErr ctxt = hang (ptext (sLit "Empty list of alterantives in") <+> pp_ctxt)
                       2 (ptext (sLit "Use -XEmptyCase to allow this"))
  where
    pp_ctxt = case ctxt of
                CaseAlt    -> ptext (sLit "case expression")
                LambdaExpr -> ptext (sLit "\\case expression")
                _ -> ptext (sLit "(unexpected)") <+> pprMatchContextNoun ctxt
 

resSigErr :: Outputable body => HsMatchContext Name -> Match RdrName body -> HsType RdrName -> SDoc 
resSigErr ctxt match ty
   = vcat [ ptext (sLit "Illegal result type signature") <+> quotes (ppr ty)
	  , nest 2 $ ptext (sLit "Result signatures are no longer supported in pattern matches")
 	  , pprMatchInCtxt ctxt match ]

rnGRHSs :: HsMatchContext Name 
        -> (Located (body RdrName) -> RnM (Located (body Name), FreeVars))
        -> GRHSs RdrName (Located (body RdrName))
        -> RnM (GRHSs Name (Located (body Name)), FreeVars)
rnGRHSs ctxt rnBody (GRHSs grhss binds)
  = rnLocalBindsAndThen binds	$ \ binds' -> do
    (grhss', fvGRHSs) <- mapFvRn (rnGRHS ctxt rnBody) grhss
    return (GRHSs grhss' binds', fvGRHSs)

rnGRHS :: HsMatchContext Name 
       -> (Located (body RdrName) -> RnM (Located (body Name), FreeVars))
       -> LGRHS RdrName (Located (body RdrName))
       -> RnM (LGRHS Name (Located (body Name)), FreeVars)
rnGRHS ctxt rnBody = wrapLocFstM (rnGRHS' ctxt rnBody)

rnGRHS' :: HsMatchContext Name 
        -> (Located (body RdrName) -> RnM (Located (body Name), FreeVars))
        -> GRHS RdrName (Located (body RdrName))
        -> RnM (GRHS Name (Located (body Name)), FreeVars)
rnGRHS' ctxt rnBody (GRHS guards rhs)
  = do	{ pattern_guards_allowed <- xoptM Opt_PatternGuards
        ; ((guards', rhs'), fvs) <- rnStmts (PatGuard ctxt) rnLExpr guards $ \ _ ->
				    rnBody rhs

	; unless (pattern_guards_allowed || is_standard_guard guards')
	  	 (addWarn (nonStdGuardErr guards'))

	; return (GRHS guards' rhs', fvs) }
  where
	-- Standard Haskell 1.4 guards are just a single boolean
	-- expression, rather than a list of qualifiers as in the
	-- Glasgow extension
    is_standard_guard []                       = True
    is_standard_guard [L _ (BodyStmt _ _ _ _)] = True
    is_standard_guard _                        = False

dupSigDeclErr :: [(Located RdrName, Sig RdrName)] -> RnM ()
dupSigDeclErr pairs@((L loc name, sig) : _)
  = addErrAt loc $
    vcat [ ptext (sLit "Duplicate") <+> what_it_is 
           <> ptext (sLit "s for") <+> quotes (ppr name)
         , ptext (sLit "at") <+> vcat (map ppr $ sort $ map (getLoc . fst) pairs) ]
  where
    what_it_is = hsSigDoc sig

dupSigDeclErr [] = panic "dupSigDeclErr"

misplacedSigErr :: LSig Name -> RnM ()
misplacedSigErr (L loc sig)
  = addErrAt loc $
    sep [ptext (sLit "Misplaced") <+> hsSigDoc sig <> colon, ppr sig]

defaultSigErr :: Sig RdrName -> SDoc
defaultSigErr sig = vcat [ hang (ptext (sLit "Unexpected default signature:"))
                              2 (ppr sig)
                         , ptext (sLit "Use -XDefaultSignatures to enable default signatures") ] 

methodBindErr :: HsBindLR RdrName RdrName -> SDoc
methodBindErr mbind
 =  hang (ptext (sLit "Pattern bindings (except simple variables) not allowed in instance declarations"))
       2 (ppr mbind)

bindsInHsBootFile :: LHsBindsLR Name RdrName -> SDoc
bindsInHsBootFile mbinds
  = hang (ptext (sLit "Bindings in hs-boot files are not allowed"))
       2 (ppr mbinds)

nonStdGuardErr :: Outputable body => [LStmtLR Name Name body] -> SDoc
nonStdGuardErr guards
  = hang (ptext (sLit "accepting non-standard pattern guards (use -XPatternGuards to suppress this message)"))
       4 (interpp'SP guards)

unusedPatBindWarn :: HsBind Name -> SDoc
unusedPatBindWarn bind
  = hang (ptext (sLit "This pattern-binding binds no variables:"))
       2 (ppr bind)