content: {-
  (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
  
  \section[RnBinds]{Renaming and dependency analysis of bindings}
  
  This module does renaming and dependency analysis on value bindings in
  the abstract syntax.  It does {\em not} do cycle-checks on class or
  type-synonym declarations; those cannot be done at this stage because
  they may be affected by renaming (which isn't fully worked out yet).
  -}
  
  module Eta.Rename.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 #-} Eta.Rename.RnExpr( rnLExpr, rnStmts )
  
  import Eta.HsSyn.HsSyn
  import Eta.TypeCheck.TcRnMonad
  import Eta.TypeCheck.TcEvidence     ( emptyTcEvBinds )
  import Eta.Rename.RnTypes
  import Eta.Rename.RnPat
  import Eta.Rename.RnNames
  import Eta.Rename.RnEnv
  import Eta.Main.DynFlags
  import Eta.BasicTypes.Module
  import Eta.BasicTypes.Name
  import Eta.BasicTypes.NameEnv
  import Eta.BasicTypes.NameSet
  import Eta.BasicTypes.RdrName          ( RdrName, rdrNameOcc )
  import Eta.BasicTypes.SrcLoc
  import Eta.Utils.ListSetOps       ( findDupsEq )
  import Eta.BasicTypes.BasicTypes       ( RecFlag(..) )
  import Eta.Utils.Digraph          ( SCC(..) )
  import Eta.Utils.Bag
  import Eta.Utils.Outputable
  import Eta.Utils.FastString
  import Data.List        ( partition, sort )
  import Eta.Utils.Maybes           ( orElse )
  import Control.Monad
  import qualified Eta.LanguageExtensions as LangExt
  -- TODO:#if __GLASGOW_HASKELL__ < 709
  -- import Data.Traversable ( traverse )
  -- #endif
  
  {-
  -- ToDo: Put the annotations into the monad, so that they arrive in the proper
  -- place and can be used when complaining.
  
  The code tree received by the function @rnBinds@ contains definitions
  in where-clauses which are all apparently mutually recursive, but which may
  not really depend upon each other. For example, in the top level program
  \begin{verbatim}
  f x = y where a = x
                y = x
  \end{verbatim}
  the definitions of @a@ and @y@ do not depend on each other at all.
  Unfortunately, the typechecker cannot always check such definitions.
  \footnote{Mycroft, A. 1984. Polymorphic type schemes and recursive
  definitions. In Proceedings of the International Symposium on Programming,
  Toulouse, pp. 217-39. LNCS 167. Springer Verlag.}
  However, the typechecker usually can check definitions in which only the
  strongly connected components have been collected into recursive bindings.
  This is precisely what the function @rnBinds@ does.
  
  ToDo: deal with case where a single monobinds binds the same variable
  twice.
  
  The vertag tag is a unique @Int@; the tags only need to be unique
  within one @MonoBinds@, so that unique-Int plumbing is done explicitly
  (heavy monad machinery not needed).
  
  
  ************************************************************************
  *                                                                      *
  * naming conventions                                                   *
  *                                                                      *
  ************************************************************************
  
  \subsection[name-conventions]{Name conventions}
  
  The basic algorithm involves walking over the tree and returning a tuple
  containing the new tree plus its free variables. Some functions, such
  as those walking polymorphic bindings (HsBinds) and qualifier lists in
  list comprehensions (@Quals@), return the variables bound in local
  environments. These are then used to calculate the free variables of the
  expression evaluated in these environments.
  
  Conventions for variable names are as follows:
  \begin{itemize}
  \item
  new code is given a prime to distinguish it from the old.
  
  \item
  a set of variables defined in @Exp@ is written @dvExp@
  
  \item
  a set of variables free in @Exp@ is written @fvExp@
  \end{itemize}
  
  ************************************************************************
  *                                                                      *
  * analysing polymorphic bindings (HsBindGroup, HsBind)
  *                                                                      *
  ************************************************************************
  
  \subsubsection[dep-HsBinds]{Polymorphic bindings}
  
  Non-recursive expressions are reconstructed without any changes at top
  level, although their component expressions may have to be altered.
  However, non-recursive expressions are currently not expected as
  \Haskell{} programs, and this code should not be executed.
  
  Monomorphic bindings contain information that is returned in a tuple
  (a @FlatMonoBinds@) containing:
  
  \begin{enumerate}
  \item
  a unique @Int@ that serves as the ``vertex tag'' for this binding.
  
  \item
  the name of a function or the names in a pattern. These are a set
  referred to as @dvLhs@, the defined variables of the left hand side.
  
  \item
  the free variables of the body. These are referred to as @fvBody@.
  
  \item
  the definition's actual code. This is referred to as just @code@.
  \end{enumerate}
  
  The function @nonRecDvFv@ returns two sets of variables. The first is
  the set of variables defined in the set of monomorphic bindings, while the
  second is the set of free variables in those bindings.
  
  The set of variables defined in a non-recursive binding is just the
  union of all of them, as @union@ removes duplicates. However, the
  free variables in each successive set of cumulative bindings is the
  union of those in the previous set plus those of the newest binding after
  the defined variables of the previous set have been removed.
  
  @rnMethodBinds@ deals only with the declarations in class and
  instance declarations.  It expects only to see @FunMonoBind@s, and
  it expects the global environment to contain bindings for the binders
  (which are all class operations).
  
  ************************************************************************
  *                                                                      *
  \subsubsection{ Top-level bindings}
  *                                                                      *
  ************************************************************************
  -}
  
  -- 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 <- tcIsHsBootOrSig
         ; if is_boot
           then rnTopBindsBoot bound_names binds
           else rnValBindsRHS (TopSigCtxt bound_names) binds }
  
  rnTopBindsBoot :: NameSet -> 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 bound_names (ValBindsIn mbinds sigs)
    = do  { checkErr (isEmptyLHsBinds mbinds) (bindsInHsBootFile mbinds)
          ; (sigs', fvs) <- renameSigs (HsBootCtxt bound_names) sigs
          ; return (ValBindsOut [] sigs', usesOnly fvs) }
  rnTopBindsBoot _ b = pprPanic "rnTopBindsBoot" (ppr b)
  
  {-
  *********************************************************
  *                                                      *
                  HsLocalBinds
  *                                                      *
  *********************************************************
  -}
  
  rnLocalBindsAndThen :: HsLocalBinds RdrName
                      -> (HsLocalBinds Name -> FreeVars -> 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 emptyNameSet
  
  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') fv_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)
  
  {-
  ************************************************************************
  *                                                                      *
                  ValBinds
  *                                                                      *
  ************************************************************************
  -}
  
  -- Renaming local binding groups
  -- 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'
               -- There should be only Ids, but if there are any bogus
               -- pattern synonyms, we'll collect them anyway, so that
               -- we don't generate subsequent out-of-scope messages
         ; 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 (wrapLocM (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 (rnLBind (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 -> FreeVars -> 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' (allUses dus)
  
                  -- 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 `unionNameSet` 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_sig emptyFsEnv decls
   where
     add_one_sig env (L loc (FixitySig names fixity)) =
       foldlM add_one env [ (loc,name_loc,name,fixity)
                          | L name_loc name <- names ]
  
     add_one env (loc, 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
            -> HsBind RdrName
            -- returns the renamed left-hand side,
            -- and the FreeVars *of the LHS*
            -- (i.e., any free variables of the pattern)
            -> RnM (HsBindLR Name RdrName)
  
  rnBindLHS name_maker _ bind@(PatBind { pat_lhs = pat })
    = do
        -- we don't actually use the FV processing of rnPatsAndThen here
        (pat',pat'_fvs) <- rnBindPat name_maker pat
        return (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 _ bind@(FunBind { fun_id = rdr_name })
    = do { name <- applyNameMaker name_maker rdr_name
         ; return (bind { fun_id   = name
                        , bind_fvs = placeHolderNamesTc }) }
  
  rnBindLHS name_maker _ (PatSynBind psb@PSB{ psb_id = rdrname })
    | isTopRecNameMaker name_maker
    = do { addLocM checkConName rdrname
         ; name <- lookupLocatedTopBndrRn rdrname   -- Should be bound at top level already
         ; return (PatSynBind psb{ psb_id = name }) }
  
    | otherwise  -- Pattern synonym, not at top level
    = do { addErr localPatternSynonymErr  -- Complain, but make up a fake
                                          -- name so that we can carry on
         ; name <- applyNameMaker name_maker rdrname
         ; return (PatSynBind psb{ psb_id = name }) }
    where
      localPatternSynonymErr :: SDoc
      localPatternSynonymErr
        = hang (ptext (sLit "Illegal pattern synonym declaration for") <+> quotes (ppr rdrname))
             2 (ptext (sLit "Pattern synonym declarations are only valid at top level"))
  
  rnBindLHS _ _ b = pprPanic "rnBindHS" (ppr b)
  
  rnLBind :: (Name -> [Name])             -- Signature tyvar function
          -> LHsBindLR Name RdrName
          -> RnM (LHsBind Name, [Name], Uses)
  rnLBind sig_fn (L loc bind)
    = setSrcSpan loc $
      do { (bind', bndrs, dus) <- rnBind sig_fn bind
         ; return (L loc bind', bndrs, dus) }
  
  -- assumes the left-hands-side vars are in scope
  rnBind :: (Name -> [Name])              -- Signature tyvar function
         -> HsBindLR Name RdrName
         -> RnM (HsBind Name, [Name], Uses)
  rnBind _ bind@(PatBind { pat_lhs = pat
                         , pat_rhs = grhss
                                     -- pat fvs were stored in bind_fvs
                                     -- after processing the LHS
                         , bind_fvs = pat_fvs })
    = 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',
                               pat_rhs_ty = placeHolderType, bind_fvs = fvs' }
                is_wild_pat = case pat of
                                L _ (WildPat {})                 -> True
                                L _ (BangPat (L _ (WildPat {}))) -> True -- #9127
                                _                                -> 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 (Reason Opt_WarnUnusedBinds) $ unusedPatBindWarn bind'
  
          ; fvs' `seq` -- See Note [Free-variable space leak]
            return (bind', bndrs, all_fvs) }
  
  rnBind sig_fn bind@(FunBind { fun_id = name
                              , fun_infix = is_infix
                              , fun_matches = matches })
         -- invariant: no free vars here when it's a FunBind
    = 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 (bind { fun_matches = matches'
                         , bind_fvs   = fvs' },
                    [plain_name], rhs_fvs)
        }
  
  rnBind sig_fn (PatSynBind bind)
    = do  { (bind', name, fvs) <- rnPatSynBind sig_fn bind
          ; return (PatSynBind bind', name, 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.
  -}
  
  rnPatSynBind :: (Name -> [Name])                -- Signature tyvar function
               -> PatSynBind Name RdrName
               -> RnM (PatSynBind Name Name, [Name], Uses)
  rnPatSynBind _sig_fn bind@(PSB { psb_id = L _ name
                                 , psb_args = details
                                 , psb_def = pat
                                 , psb_dir = dir })
         -- invariant: no free vars here when it's a FunBind
    = do  { pattern_synonym_ok <- xoptM LangExt.PatternSynonyms
          ; unless pattern_synonym_ok (addErr patternSynonymErr)
  
          ; ((pat', details'), fvs1) <- rnPat PatSyn pat $ \pat' -> do
           -- We check the 'RdrName's instead of the 'Name's
           -- so that the binding locations are reported
           -- from the left-hand side
          { (details', fvs) <- case details of
                 PrefixPatSyn vars ->
                     do { checkDupRdrNames vars
                        ; names <- mapM lookupVar vars
                        ; return (PrefixPatSyn names, mkFVs (map unLoc names)) }
                 InfixPatSyn var1 var2 ->
                     do { checkDupRdrNames [var1, var2]
                        ; name1 <- lookupVar var1
                        ; name2 <- lookupVar var2
                        -- ; checkPrecMatch -- TODO
                        ; return (InfixPatSyn name1 name2, mkFVs (map unLoc [name1, name2])) }
          ; return ((pat', details'), fvs) }
          ; (dir', fvs2) <- case dir of
              Unidirectional -> return (Unidirectional, emptyFVs)
              ImplicitBidirectional -> return (ImplicitBidirectional, emptyFVs)
              ExplicitBidirectional mg ->
                  do { (mg', fvs) <- rnMatchGroup PatSyn rnLExpr mg
                     ; return (ExplicitBidirectional mg', fvs) }
  
          ; mod <- getModule
          ; let fvs = fvs1 `plusFV` fvs2
                fvs' = filterNameSet (nameIsLocalOrFrom mod) fvs
                  -- Keep locally-defined Names
                  -- As well as dependency analysis, we need these for the
                  -- MonoLocalBinds test in TcBinds.decideGeneralisationPlan
  
          ; let bind' = bind{ psb_args = details'
                            , psb_def = pat'
                            , psb_dir = dir'
                            , psb_fvs = fvs' }
  
          ; fvs' `seq` -- See Note [Free-variable space leak]
            return (bind', [name], fvs1)
            -- See Note [Pattern synonym wrappers don't yield dependencies]
        }
    where
      lookupVar = wrapLocM lookupOccRn
  
      patternSynonymErr :: SDoc
      patternSynonymErr
        = hang (ptext (sLit "Illegal pattern synonym declaration"))
             2 (ptext (sLit "Use -XPatternSynonyms to enable this extension"))
  
  {-
  Note [Pattern synonym wrappers don't yield dependencies]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  When renaming a pattern synonym that has an explicit wrapper,
  references in the wrapper definition should not be used when
  calculating dependencies. For example, consider the following pattern
  synonym definition:
  
  pattern P x <- C1 x where
    P x = f (C1 x)
  
  f (P x) = C2 x
  
  In this case, 'P' needs to be typechecked in two passes:
  
  1. Typecheck the pattern definition of 'P', which fully determines the
  type of 'P'. This step doesn't require knowing anything about 'f',
  since the wrapper definition is not looked at.
  
  2. Typecheck the wrapper definition, which needs the typechecked
  definition of 'f' to be in scope.
  
  This behaviour is implemented in 'tcValBinds', but it crucially
  depends on 'P' not being put in a recursive group with 'f' (which
  would make it look like a recursive pattern synonym a la 'pattern P =
  P' which is unsound and rejected).
  
  -}
  
  ---------------------
  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) -> nameSetElems 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 = unionNameSets [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
      extractScopedTyVars :: LHsType Name -> [Name]
      extractScopedTyVars (L _ (HsForAllTy Explicit _ ltvs _ _)) = hsLKiTyVarNames ltvs
      extractScopedTyVars _ = []
  
      env :: NameEnv [Name]
      env = mkNameEnv [ (name, nwcs ++ extractScopedTyVars ty)  -- Kind variables and type variables
                      | L _ (TypeSig names ty nwcs _) <- 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@ is used for the method bindings of a class and an instance
  declaration.   Like @rnBinds@ but without dependency analysis.
  
  NOTA BENE: we record each {\em binder} of a method-bind group as a free variable.
  That's crucial when dealing with an instance decl:
  \begin{verbatim}
          instance Foo (T a) where
             op x = ...
  \end{verbatim}
  This might be the {\em sole} occurrence of @op@ for an imported class @Foo@,
  and unless @op@ occurs we won't treat the type signature of @op@ in the class
  decl for @Foo@ as a source of instance-decl gates.  But we should!  Indeed,
  in many ways the @op@ in an instance decl is just like an occurrence, not
  a binder.
  -}
  
  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
                                                       , mg_origin = origin } }))
    = 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 = mkMatchGroupName origin 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)
  
  -- Associated pattern synonyms are not implemented yet
  rnMethodBind _ _ (L loc bind@(PatSynBind {})) = do
      addErrAt loc $ methodPatSynErr bind
      return (emptyBag, emptyFVs)
  
  rnMethodBind _ _ b = pprPanic "rnMethodBind" (ppr b)
  
  {-
  ************************************************************************
  *                                                                      *
  \subsubsection[dep-Sigs]{Signatures (and user-pragmas for values)}
  *                                                                      *
  ************************************************************************
  
  @renameSigs@ checks for:
  \begin{enumerate}
  \item more than one sig for one thing;
  \item signatures given for things not bound here;
  \end{enumerate}
  
  At the moment we don't gather free-var info from the types in
  signatures.  We'd only need this if we wanted to report unused tyvars.
  -}
  
  renameSigs :: HsSigCtxt
             -> [LSig RdrName]
             -> RnM ([LSig Name], FreeVars)
  -- Renames the signatures and performs error checks
  renameSigs ctxt sigs
    = do  { mapM_ dupSigDeclErr (findDupSigs sigs)
  
          ; checkDupMinimalSigs 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
          -- (named and anonymous) wildcards are bound here.
          ; (wcs, ty') <- extractWildcards ty
          ; bindLocatedLocalsFV wcs $ \wcs_new -> do {
            (new_ty, fvs) <- rnHsSigType (ppr_sig_bndrs vs) ty'
          ; return (TypeSig new_vs new_ty wcs_new [], fvs) } }
  
  renameSig ctxt sig@(GenericSig vs ty)
    = do  { defaultSigs_on <- xoptM LangExt.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 src ty)
    = do  { (new_ty, fvs) <- rnLHsType SpecInstSigCtx ty
          ; return (SpecInstSig src 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 tys inl)
    = do  { new_v <- case ctxt of
                       TopSigCtxt {} -> lookupLocatedOccRn v
                       _             -> lookupSigOccRn ctxt sig v
          -- ; (new_ty, fvs) <- rnHsSigType (quotes (ppr v)) ty
          ; (new_ty, fvs) <- foldM do_one ([],emptyFVs) tys
          ; return (SpecSig new_v new_ty inl, fvs) }
    where
      do_one (tys,fvs) ty
        = do { (new_ty, fvs_ty) <- rnHsSigType (quotes (ppr v)) ty
             ; return ( new_ty:tys, fvs_ty `plusFV` 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 vs f))
    = do  { new_vs <- mapM (lookupSigOccRn ctxt sig) vs
          ; return (FixSig (FixitySig new_vs f), emptyFVs) }
  
  renameSig ctxt sig@(MinimalSig s bf)
    = do new_bf <- traverse (lookupSigOccRn ctxt sig) bf
         return (MinimalSig s new_bf, emptyFVs)
  
  renameSig ctxt sig@(PatSynSig v (flag, qtvs) prov req ty)
    = do  { v' <- lookupSigOccRn ctxt sig v
          ; let doc = TypeSigCtx $ quotes (ppr v)
          ; loc <- getSrcSpanM
  
          ; let (tv_kvs, mentioned) = extractHsTysRdrTyVars (ty:unLoc prov ++ unLoc req)
          ; tv_bndrs <- case flag of
              Implicit ->
                  return $ mkHsQTvs . userHsTyVarBndrs loc $ mentioned
              Explicit ->
                  do { let heading = ptext (sLit "In the pattern synonym type signature")
                                     <+> quotes (ppr sig)
                     ; warnUnusedForAlls (heading $$ docOfHsDocContext doc) qtvs mentioned
                     ; return qtvs }
              Qualified -> panic "renameSig: Qualified"
  
          ; bindHsTyVars doc Nothing tv_kvs tv_bndrs $ \ tyvars -> do
          { (prov', fvs1) <- rnContext doc prov
          ; (req', fvs2) <- rnContext doc req
          ; (ty', fvs3) <- rnLHsType doc ty
  
          ; let fvs = plusFVs [fvs1, fvs2, fvs3]
          ; return (PatSynSig v' (flag, tyvars) prov' req' ty', fvs) }}
  
  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
  
       (PatSynSig {}, TopSigCtxt{}) -> True
       (PatSynSig {}, _)            -> False
  
       (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
  
       (MinimalSig {}, ClsDeclCtxt {}) -> True
       (MinimalSig {}, _)              -> 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 ns _)) = zip ns (repeat 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
  
  -- Warn about multiple MINIMAL signatures
  checkDupMinimalSigs :: [LSig RdrName] -> RnM ()
  checkDupMinimalSigs sigs
    = case filter isMinimalLSig sigs of
        minSigs@(_:_:_) -> dupMinimalSigErr minSigs
        _ -> return ()
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection{Match}
  *                                                                      *
  ************************************************************************
  -}
  
  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, mg_origin = origin })
    = do { empty_case_ok <- xoptM LangExt.EmptyCase
         ; when (null ms && not empty_case_ok) (addErr (emptyCaseErr ctxt))
         ; (new_ms, ms_fvs) <- mapFvRn (rnMatch ctxt rnBody) ms
         ; return (mkMatchGroupName origin 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 { m_fun_id_infix = mf, m_pats = pats
                                    , m_type = maybe_rhs_sig, m_grhss = 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
          ; let mf' = case (ctxt,mf) of
                        (FunRhs funid isinfix,Just (L lf _,_))
                                                      -> Just (L lf funid,isinfix)
                        _                             -> Nothing
          ; return (Match { m_fun_id_infix = mf', m_pats = pats'
                          , m_type = Nothing, m_grhss = grhss'}, grhss_fvs ) }}
  
  emptyCaseErr :: HsMatchContext Name -> SDoc
  emptyCaseErr ctxt = hang (ptext (sLit "Empty list of alternatives in") <+> pp_ctxt)
                         2 (ptext (sLit "Use EmptyCase 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 ]
  
  {-
  ************************************************************************
  *                                                                      *
  \subsubsection{Guarded right-hand sides (GRHSs)}
  *                                                                      *
  ************************************************************************
  -}
  
  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 LangExt.PatternGuards
          ; ((guards', rhs'), fvs) <- rnStmts (PatGuard ctxt) rnLExpr guards $ \ _ ->
                                      rnBody rhs
  
          ; unless (pattern_guards_allowed || is_standard_guard guards')
                   (addWarn NoReason (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
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection{Error messages}
  *                                                                      *
  ************************************************************************
  -}
  
  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 DefaultSignatures 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)
  
  methodPatSynErr :: HsBindLR RdrName RdrName -> SDoc
  methodPatSynErr mbind
   =  hang (ptext (sLit "Pattern synonyms not allowed in class/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 PatternGuards 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)
  
  dupMinimalSigErr :: [LSig RdrName] -> RnM ()
  dupMinimalSigErr sigs@(L loc _ : _)
    = addErrAt loc $
      vcat [ ptext (sLit "Multiple minimal complete definitions")
           , ptext (sLit "at") <+> vcat (map ppr $ sort $ map getLoc sigs)
           , ptext (sLit "Combine alternative minimal complete definitions with `|'") ]
  dupMinimalSigErr [] = panic "dupMinimalSigErr"
  