Refactor ConDeclwip/T11028

The ConDecl type in HsDecls is an uneasy compromise. For the most part,
HsSyn directly reflects the syntax written by the programmer; and that
gives just the right "pegs" on which to hang Alan's API annotations. But
ConDecl doesn't properly reflect the syntax of Haskell-98 and GADT-style
data type declarations.

To be concrete, here's a draft new data type

data ConDecl name
  | ConDeclGADT
      { con_names   :: [Located name]
      , con_type    :: LHsSigType name  -- The type after the ‘::’
      , con_doc     :: Maybe LHsDocString }

  | ConDeclH98
      { con_name    :: Located name

      , con_qvars     :: Maybe (LHsQTyVars name)
        -- User-written forall (if any), and its implicit
        -- kind variables
        -- Non-Nothing needs -XExistentialQuantification

      , con_cxt       :: Maybe (LHsContext name)
        -- ^ User-written context (if any)

      , con_details   :: HsConDeclDetails name
          -- ^ Arguments

      , con_doc       :: Maybe LHsDocString
          -- ^ A possible Haddock comment.
      } deriving (Typeable)

Note that

    For GADTs, just keep a type. That's what the user writes.
    NB:HsType can represent records on the LHS of an arrow:

      { x:Int,y:Bool} -> T

    con_qvars and con_cxt are both Maybe because they are both
    optional (the forall and the context of an existential data type

    For ConDeclGADT the type variables of the data type do not scope
    over the con_type; whereas for ConDeclH98 they do scope over con_cxt
    and con_details.

Trac issue: #11028

1 files changed, 10 insertions, 1 deletions

diff --git a/compiler/rename/RnNames.hs b/compiler/rename/RnNames.hs
index b0b79f55e6..3cbb887693 100644
--- a/compiler/rename/RnNames.hs
+++ b/compiler/rename/RnNames.hs
@@ -610,11 +610,20 @@ getLocalNonValBinders fixity_env
     mk_fld_env :: HsDataDefn RdrName -> [Name] -> [FieldLabel] -> [(Name, [FieldLabel])]
     mk_fld_env d names flds = concatMap find_con_flds (dd_cons d)
       where
-        find_con_flds (L _ (ConDecl { con_names   = rdrs
+        find_con_flds (L _ (ConDeclH98 { con_name   = rdrs
                                     , con_details = RecCon cdflds }))
             = map (\ (L _ rdr) -> ( find_con_name rdr
                                   , concatMap find_con_decl_flds (unLoc cdflds)))
+                  [rdrs] -- AZ:TODO remove map
+        find_con_flds (L _ (ConDeclGADT { con_names = rdrs, con_type = (HsIB { hsib_body = res_ty})}))
+            = map (\ (L _ rdr) -> ( find_con_name rdr
+                                  , concatMap find_con_decl_flds cdflds))
                   rdrs
+            where
+              (_tvs, _cxt, tau) = splitLHsSigmaTy res_ty
+              cdflds = case tau of
+                 L _ (HsFunTy (L _ (HsRecTy flds)) _) -> flds
+                 _                                    -> []
         find_con_flds _ = []
 
         find_con_name rdr