Refactor treatment of wildcards

This patch began as a modest refactoring of HsType and friends, to
clarify and tidy up exactly where quantification takes place in types.
Although initially driven by making the implementation of wildcards more
tidy (and fixing a number of bugs), I gradually got drawn into a pretty
big process, which I've been doing on and off for quite a long time.

There is one compiler performance regression as a result of all
this, in perf/compiler/T3064.  I still need to look into that.

* The principal driving change is described in Note [HsType binders]
  in HsType.  Well worth reading!

* Those data type changes drive almost everything else.  In particular
  we now statically know where

       (a) implicit quantification only (LHsSigType),
           e.g. in instance declaratios and SPECIALISE signatures

       (b) implicit quantification and wildcards (LHsSigWcType)
           can appear, e.g. in function type signatures

* As part of this change, HsForAllTy is (a) simplified (no wildcards)
  and (b) split into HsForAllTy and HsQualTy.  The two contructors
  appear when and only when the correponding user-level construct
  appears.  Again see Note [HsType binders].

  HsExplicitFlag disappears altogether.

* Other simplifications

     - ExprWithTySig no longer needs an ExprWithTySigOut variant

     - TypeSig no longer needs a PostRn name [name] field
       for wildcards

     - PatSynSig records a LHsSigType rather than the decomposed
       pieces

     - The mysterious 'GenericSig' is now 'ClassOpSig'

* Renamed LHsTyVarBndrs to LHsQTyVars

* There are some uninteresting knock-on changes in Haddock,
  because of the HsSyn changes

I also did a bunch of loosely-related changes:

* We already had type synonyms CoercionN/CoercionR for nominal and
  representational coercions.  I've added similar treatment for

      TcCoercionN/TcCoercionR

      mkWpCastN/mkWpCastN

  All just type synonyms but jolly useful.

* I record-ised ForeignImport and ForeignExport

* I improved the (poor) fix to Trac #10896, by making
  TcTyClsDecls.checkValidTyCl recover from errors, but adding a
  harmless, abstract TyCon to the envt if so.

* I did some significant refactoring in RnEnv.lookupSubBndrOcc,
  for reasons that I have (embarrassingly) now totally forgotten.
  It had to do with something to do with import and export

Updates haddock submodule.

1 files changed, 84 insertions, 56 deletions

diff --git a/compiler/hsSyn/HsDecls.hs b/compiler/hsSyn/HsDecls.hs
index f75fff10af..b8612ed2be 100644
--- a/compiler/hsSyn/HsDecls.hs
+++ b/compiler/hsSyn/HsDecls.hs
@@ -19,7 +19,8 @@
 -- @InstDecl@, @DefaultDecl@ and @ForeignDecl@.
 module HsDecls (
   -- * Toplevel declarations
-  HsDecl(..), LHsDecl, HsDataDefn(..),
+  HsDecl(..), LHsDecl, HsDataDefn(..), HsDeriving,
+
   -- ** Class or type declarations
   TyClDecl(..), LTyClDecl,
   TyClGroup(..), tyClGroupConcat, mkTyClGroup,
@@ -481,10 +482,10 @@ data TyClDecl name
     --             'ApiAnnotation.AnnEqual',
 
     -- For details on above see note [Api annotations] in ApiAnnotation
-    SynDecl { tcdLName  :: Located name            -- ^ Type constructor
-            , tcdTyVars :: LHsTyVarBndrs name      -- ^ Type variables; for an associated type
+    SynDecl { tcdLName  :: Located name           -- ^ Type constructor
+            , tcdTyVars :: LHsQTyVars name        -- ^ Type variables; for an associated type
                                                   --   these include outer binders
-            , tcdRhs    :: LHsType name            -- ^ RHS of type declaration
+            , tcdRhs    :: LHsType name           -- ^ RHS of type declaration
             , tcdFVs    :: PostRn name NameSet }
 
   | -- | @data@ declaration
@@ -497,7 +498,7 @@ data TyClDecl name
 
     -- For details on above see note [Api annotations] in ApiAnnotation
     DataDecl { tcdLName    :: Located name        -- ^ Type constructor
-             , tcdTyVars   :: LHsTyVarBndrs name  -- ^ Type variables; for an associated type
+             , tcdTyVars   :: LHsQTyVars name  -- ^ Type variables; for an associated type
                                                   --   these include outer binders
                                                   -- Eg  class T a where
                                                   --       type F a :: *
@@ -509,7 +510,7 @@ data TyClDecl name
 
   | ClassDecl { tcdCtxt    :: LHsContext name,          -- ^ Context...
                 tcdLName   :: Located name,             -- ^ Name of the class
-                tcdTyVars  :: LHsTyVarBndrs name,       -- ^ Class type variables
+                tcdTyVars  :: LHsQTyVars name,          -- ^ Class type variables
                 tcdFDs     :: [Located (FunDep (Located name))],
                                                         -- ^ Functional deps
                 tcdSigs    :: [LSig name],              -- ^ Methods' signatures
@@ -548,7 +549,6 @@ tyClGroupConcat = concatMap group_tyclds
 mkTyClGroup :: [LTyClDecl name] -> TyClGroup name
 mkTyClGroup decls = TyClGroup { group_tyclds = decls, group_roles = [] }
 
-
 -- Simple classifiers for TyClDecl
 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -613,7 +613,7 @@ tyClDeclLName decl = tcdLName decl
 tcdName :: TyClDecl name -> name
 tcdName = unLoc . tyClDeclLName
 
-tyClDeclTyVars :: TyClDecl name -> LHsTyVarBndrs name
+tyClDeclTyVars :: TyClDecl name -> LHsQTyVars name
 tyClDeclTyVars (FamDecl { tcdFam = FamilyDecl { fdTyVars = tvs } }) = tvs
 tyClDeclTyVars d = tcdTyVars d
 
@@ -685,7 +685,7 @@ instance OutputableBndr name => Outputable (TyClGroup name) where
 
 pp_vanilla_decl_head :: OutputableBndr name
    => Located name
-   -> LHsTyVarBndrs name
+   -> LHsQTyVars name
    -> HsContext name
    -> SDoc
 pp_vanilla_decl_head thing tyvars context
@@ -796,7 +796,7 @@ type LFamilyDecl name = Located (FamilyDecl name)
 data FamilyDecl name = FamilyDecl
   { fdInfo           :: FamilyInfo name              -- type/data, closed/open
   , fdLName          :: Located name                 -- type constructor
-  , fdTyVars         :: LHsTyVarBndrs name           -- type variables
+  , fdTyVars         :: LHsQTyVars name              -- type variables
   , fdResultSig      :: LFamilyResultSig name        -- result signature
   , fdInjectivityAnn :: Maybe (LInjectivityAnn name) -- optional injectivity ann
   }
@@ -960,26 +960,31 @@ data HsDataDefn name   -- The payload of a data type defn
                      -- For @data T a where { T1 :: T a }@
                      --   the 'LConDecls' all have 'ResTyGADT'.
 
-                 dd_derivs :: Maybe (Located [LHsType name])
-                     -- ^ Derivings; @Nothing@ => not specified,
-                     --              @Just []@ => derive exactly what is asked
-                     --
-                     -- These "types" must be of form
-                     -- @
-                     --      forall ab. C ty1 ty2
-                     -- @
-                     -- Typically the foralls and ty args are empty, but they
-                     -- are non-empty for the newtype-deriving case
-                     --
-                     --  - 'ApiAnnotation.AnnKeywordId' :
-                     --       'ApiAnnotation.AnnDeriving',
-                     --       'ApiAnnotation.AnnOpen','ApiAnnotation.AnnClose'
+                 dd_derivs :: HsDeriving name  -- ^ Optional 'deriving' claues
 
              -- For details on above see note [Api annotations] in ApiAnnotation
    }
     deriving( Typeable )
 deriving instance (DataId id) => Data (HsDataDefn id)
 
+type HsDeriving name = Maybe (Located [LHsSigType name])
+  -- ^ The optional 'deriving' clause of a data declaration
+  --
+  --   @Nothing@ => not specified,
+  --   @Just []@ => derive exactly what is asked
+  --
+  -- It's a 'LHsSigType' because, with Generalised Newtype
+  -- Deriving, we can mention type variables that aren't
+  -- bound by the date type.   e.g.
+  --     data T b = ... deriving( C [a] )
+  -- should producd a derived instance for (C [a] (T b))
+  --
+  -- The payload of the Maybe is Located so that we have a
+  -- place to hang the API annotations:
+  --  - 'ApiAnnotation.AnnKeywordId' :
+  --       'ApiAnnotation.AnnDeriving',
+  --       'ApiAnnotation.AnnOpen','ApiAnnotation.AnnClose'
+
 data NewOrData
   = NewType                     -- ^ @newtype Blah ...@
   | DataType                    -- ^ @data Blah ...@
@@ -1021,17 +1026,28 @@ data ConDecl name
         -- the user-callable wrapper Id.
         -- It is a list to deal with GADT constructors of the form
         --   T1, T2, T3 :: <payload>
-    , con_explicit  :: HsExplicitFlag
-        -- ^ Is there an user-written forall? (cf. 'HsTypes.HsForAllTy')
 
-    , con_qvars     :: LHsTyVarBndrs name
+    , con_explicit  :: Bool
+        -- ^ Is there an user-written forall?
+        -- For ResTyH98, "explicit" means something like:
+        --     data T = forall a. MkT { x :: a -> a }
+        -- For ResTyGADT, "explicit" means something like
+        --     data T where { MkT :: forall a. <blah> }
+
+    , con_qvars     :: LHsQTyVars name
         -- ^ Type variables.  Depending on 'con_res' this describes the
         -- following entities
         --
         --  - ResTyH98:  the constructor's *existential* type variables
+        --               e.g. data T a = forall b. MkT b (b->a)
+        --               con_qvars = {b}
+        --
         --  - ResTyGADT: *all* the constructor's quantified type variables
+        --               e.g.  data T a where
+        --                       MkT :: forall a b. b -> (b->a) -> T a
+        --               con_qvars = {a,b}
         --
-        -- If con_explicit is Implicit, then con_qvars is irrelevant
+        -- If con_explicit is False, then con_qvars is irrelevant
         -- until after renaming.
 
     , con_cxt       :: LHsContext name
@@ -1087,9 +1103,9 @@ pp_data_defn pp_hdr (HsDataDefn { dd_ND = new_or_data, dd_ctxt = L _ context
                Nothing   -> empty
                Just kind -> dcolon <+> ppr kind
     pp_derivings = case derivings of
-                     Nothing       -> empty
-                     Just (L _ ds) -> hsep [ptext (sLit "deriving"),
-                                            parens (interpp'SP ds)]
+                     Nothing -> empty
+                     Just (L _ ds) -> hsep [ ptext (sLit "deriving")
+                                           , parens (interpp'SP ds)]
 
 instance OutputableBndr name => Outputable (HsDataDefn name) where
    ppr d = pp_data_defn (\_ -> ptext (sLit "Naked HsDataDefn")) d
@@ -1112,7 +1128,7 @@ pprConDecl (ConDecl { con_names = [L _ con]  -- NB: non-GADT means 1 con
                     , con_explicit = expl, con_qvars = tvs
                     , con_cxt = cxt, con_details = details
                     , con_res = ResTyH98, con_doc = doc })
-  = sep [ppr_mbDoc doc, pprHsForAll expl tvs cxt, ppr_details details]
+  = sep [ppr_mbDoc doc, ppr_con_forall expl tvs cxt, ppr_details details]
   where
     ppr_details (InfixCon t1 t2) = hsep [ppr t1, pprInfixOcc con, ppr t2]
     ppr_details (PrefixCon tys)  = hsep (pprPrefixOcc con
@@ -1124,7 +1140,7 @@ pprConDecl (ConDecl { con_names = cons, con_explicit = expl, con_qvars = tvs
                     , con_cxt = cxt, con_details = PrefixCon arg_tys
                     , con_res = ResTyGADT _ res_ty, con_doc = doc })
   = ppr_mbDoc doc <+> ppr_con_names cons <+> dcolon <+>
-    sep [pprHsForAll expl tvs cxt, ppr (foldr mk_fun_ty res_ty arg_tys)]
+    sep [ppr_con_forall expl tvs cxt, ppr (foldr mk_fun_ty res_ty arg_tys)]
   where
     mk_fun_ty a b = noLoc (HsFunTy a b)
 
@@ -1132,7 +1148,7 @@ pprConDecl (ConDecl { con_names = cons, con_explicit = expl, con_qvars = tvs
                     , con_cxt = cxt, con_details = RecCon fields
                     , con_res = ResTyGADT _ res_ty, con_doc = doc })
   = sep [ppr_mbDoc doc <+> ppr_con_names cons <+> dcolon
-         <+> pprHsForAll expl tvs cxt,
+         <+> ppr_con_forall expl tvs cxt,
          pprConDeclFields (unLoc fields) <+> arrow <+> ppr res_ty]
 
 pprConDecl decl@(ConDecl { con_details = InfixCon ty1 ty2, con_res = ResTyGADT {} })
@@ -1145,6 +1161,14 @@ pprConDecl decl@(ConDecl { con_details = InfixCon ty1 ty2, con_res = ResTyGADT {
 -- than one constructor, which should indeed be impossible
 pprConDecl (ConDecl { con_names = cons }) = pprPanic "pprConDecl" (ppr cons)
 
+ppr_con_forall :: OutputableBndr name => Bool -> LHsQTyVars name
+                                      -> LHsContext name -> SDoc
+ppr_con_forall explicit_forall qtvs (L _ ctxt)
+  | explicit_forall
+  = pprHsForAllTvs (hsQTvBndrs qtvs) <+> pprHsContext ctxt
+  | otherwise
+  = pprHsContext ctxt
+
 ppr_con_names :: (OutputableBndr name) => [Located name] -> SDoc
 ppr_con_names = pprWithCommas (pprPrefixOcc . unLoc)
 
@@ -1183,12 +1207,12 @@ type LTyFamInstEqn  name = Located (TyFamInstEqn  name)
 
 type LTyFamDefltEqn name = Located (TyFamDefltEqn name)
 
-type HsTyPats name = HsWithBndrs name [LHsType name]
+type HsTyPats name = HsImplicitBndrs name [LHsType name]
             -- ^ Type patterns (with kind and type bndrs)
             -- See Note [Family instance declaration binders]
 
 type TyFamInstEqn  name = TyFamEqn name (HsTyPats name)
-type TyFamDefltEqn name = TyFamEqn name (LHsTyVarBndrs name)
+type TyFamDefltEqn name = TyFamEqn name (LHsQTyVars name)
   -- See Note [Type family instance declarations in HsSyn]
 
 -- | One equation in a type family instance declaration
@@ -1244,9 +1268,9 @@ deriving instance (DataId name) => Data (DataFamInstDecl name)
 type LClsInstDecl name = Located (ClsInstDecl name)
 data ClsInstDecl name
   = ClsInstDecl
-      { cid_poly_ty :: LHsType name    -- Context => Class Instance-type
-                                       -- Using a polytype means that the renamer conveniently
-                                       -- figures out the quantified type variables for us.
+      { cid_poly_ty :: LHsSigType name    -- Context => Class Instance-type
+                                          -- Using a polytype means that the renamer conveniently
+                                          -- figures out the quantified type variables for us.
       , cid_binds         :: LHsBinds name           -- Class methods
       , cid_sigs          :: [LSig name]             -- User-supplied pragmatic info
       , cid_tyfam_insts   :: [LTyFamInstDecl name]   -- Type family instances
@@ -1344,7 +1368,7 @@ pp_fam_inst_lhs :: OutputableBndr name
    -> HsTyPats name
    -> HsContext name
    -> SDoc
-pp_fam_inst_lhs thing (HsWB { hswb_cts = typats }) context -- explicit type patterns
+pp_fam_inst_lhs thing (HsIB { hsib_body = typats }) context -- explicit type patterns
    = hsep [ pprHsContext context, pprPrefixOcc (unLoc thing)
           , hsep (map (pprParendHsType.unLoc) typats)]
 
@@ -1404,7 +1428,7 @@ instDeclDataFamInsts inst_decls
 type LDerivDecl name = Located (DerivDecl name)
 
 data DerivDecl name = DerivDecl
-        { deriv_type :: LHsType name
+        { deriv_type         :: LHsSigType name
         , deriv_overlap_mode :: Maybe (Located OverlapMode)
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen',
          --                                    'ApiAnnotation.AnnClose',
@@ -1466,14 +1490,17 @@ instance (OutputableBndr name)
 type LForeignDecl name = Located (ForeignDecl name)
 
 data ForeignDecl name
-  = ForeignImport (Located name) -- defines this name
-                  (LHsType name) -- sig_ty
-                  (PostTc name Coercion) -- rep_ty ~ sig_ty
-                  ForeignImport
-  | ForeignExport (Located name) -- uses this name
-                  (LHsType name) -- sig_ty
-                  (PostTc name Coercion)  -- sig_ty ~ rep_ty
-                  ForeignExport
+  = ForeignImport
+      { fd_name   :: Located name          -- defines this name
+      , fd_sig_ty :: LHsSigType name       -- sig_ty
+      , fd_co     :: PostTc name Coercion  -- rep_ty ~ sig_ty
+      , fd_fi     :: ForeignImport }
+
+  | ForeignExport
+      { fd_name   :: Located name          -- uses this name
+      , fd_sig_ty :: LHsSigType name       -- sig_ty
+      , fd_co     :: PostTc name Coercion  -- rep_ty ~ sig_ty
+      , fd_fe     :: ForeignExport }
         -- ^
         --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnForeign',
         --           'ApiAnnotation.AnnImport','ApiAnnotation.AnnExport',
@@ -1481,6 +1508,7 @@ data ForeignDecl name
 
         -- For details on above see note [Api annotations] in ApiAnnotation
   deriving (Typeable)
+
 deriving instance (DataId name) => Data (ForeignDecl name)
 {-
     In both ForeignImport and ForeignExport:
@@ -1543,10 +1571,10 @@ data ForeignExport = CExport  (Located CExportSpec) -- contains the calling
 --
 
 instance OutputableBndr name => Outputable (ForeignDecl name) where
-  ppr (ForeignImport n ty _ fimport) =
-    hang (ptext (sLit "foreign import") <+> ppr fimport <+> ppr n)
-       2 (dcolon <+> ppr ty)
-  ppr (ForeignExport n ty _ fexport) =
+  ppr (ForeignImport { fd_name = n, fd_sig_ty = ty, fd_fi = fimport })
+    = hang (ptext (sLit "foreign import") <+> ppr fimport <+> ppr n)
+         2 (dcolon <+> ppr ty)
+  ppr (ForeignExport { fd_name = n, fd_sig_ty = ty, fd_fe = fexport }) =
     hang (ptext (sLit "foreign export") <+> ppr fexport <+> ppr n)
        2 (dcolon <+> ppr ty)
 
@@ -1621,7 +1649,7 @@ flattenRuleDecls decls = concatMap (rds_rules . unLoc) decls
 type LRuleBndr name = Located (RuleBndr name)
 data RuleBndr name
   = RuleBndr (Located name)
-  | RuleBndrSig (Located name) (HsWithBndrs name (LHsType name))
+  | RuleBndrSig (Located name) (LHsSigWcType name)
         -- ^
         --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen',
         --     'ApiAnnotation.AnnDcolon','ApiAnnotation.AnnClose'
@@ -1630,7 +1658,7 @@ data RuleBndr name
   deriving (Typeable)
 deriving instance (DataId name) => Data (RuleBndr name)
 
-collectRuleBndrSigTys :: [RuleBndr name] -> [HsWithBndrs name (LHsType name)]
+collectRuleBndrSigTys :: [RuleBndr name] -> [LHsSigWcType name]
 collectRuleBndrSigTys bndrs = [ty | RuleBndrSig _ ty <- bndrs]
 
 instance OutputableBndr name => Outputable (RuleDecls name) where
@@ -1709,7 +1737,7 @@ data VectDecl name
   | HsVectClassOut              -- post type-checking
       Class
   | HsVectInstIn                -- pre type-checking (always SCALAR)  !!!FIXME: should be superfluous now
-      (LHsType name)
+      (LHsSigType name)
   | HsVectInstOut               -- post type-checking (always SCALAR) !!!FIXME: should be superfluous now
       ClsInst
   deriving (Typeable)