Fix Trac #3012: allow more free-wheeling in standalone deriving

[ghc-hetmet.git] / compiler / typecheck / TcEnv.lhs

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index 8c37e08..055fc2c 100644 (file)
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -70,11 +70,9 @@ import TypeRep
 import Class
 import Name
 import NameEnv
-import OccName
 import HscTypes
 import SrcLoc
 import Outputable
-import Maybes
 import Unique
 import FastString
 \end{code}
@@ -126,11 +124,8 @@ tcLookupGlobal name
        }}}}}
 
 tcLookupField :: Name -> TcM Id                -- Returns the selector Id
-tcLookupField name = do
-    thing <- tcLookup name     -- Note [Record field lookup]
-    case thing of
-       AGlobal (AnId id) -> return id
-       thing -> wrongThingErr "field name" thing name
+tcLookupField name 
+  = tcLookupId name    -- Note [Record field lookup]
 
 {- Note [Record field lookup]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -176,9 +171,13 @@ tcLookupLocatedTyCon = addLocM tcLookupTyCon
 
 -- Look up the instance tycon of a family instance.
 --
--- The match must be unique - ie, match exactly one instance - but the 
--- type arguments used for matching may be more specific than those of 
--- the family instance declaration.
+-- The match may be ambiguous (as we know that overlapping instances have
+-- identical right-hand sides under overlapping substitutions - see
+-- 'FamInstEnv.lookupFamInstEnvConflicts').  However, the type arguments used
+-- for matching must be equal to or be more specific than those of the family
+-- instance declaration.  We pick one of the matches in case of ambiguity; as
+-- the right-hand sides are identical under the match substitution, the choice
+-- does not matter.
 --
 -- Return the instance tycon and its type instance.  For example, if we have
 --
@@ -199,9 +198,9 @@ tcLookupFamInst tycon tys
        ; eps <- getEps
        ; let instEnv = (eps_fam_inst_env eps, tcg_fam_inst_env env)
        ; case lookupFamInstEnv instEnv tycon tys of
-          [(fam_inst, rep_tys)] -> return $ Just (famInstTyCon fam_inst, 
-                                                   rep_tys)
-          _                     -> return Nothing
+          []                      -> return Nothing
+          ((fam_inst, rep_tys):_) 
+             -> return $ Just (famInstTyCon fam_inst, rep_tys)
        }
 \end{code}
 
@@ -641,6 +640,7 @@ data InstBindings a
        (LHsBinds a)            -- Bindings for the instance methods
        [LSig a]                -- User pragmas recorded for generating 
                                -- specialised instances
+       Bool                    -- True <=> This code came from a standalone deriving clause
 
   | NewTypeDerived              -- Used for deriving instances of newtypes, where the
        CoercionI               -- witness dictionary is identical to the argument 
@@ -656,8 +656,8 @@ pprInstInfo info = vcat [ptext (sLit "InstInfo:") <+> ppr (idType (iDFunId info)
 pprInstInfoDetails :: OutputableBndr a => InstInfo a -> SDoc
 pprInstInfoDetails info = pprInstInfo info $$ nest 2 (details (iBinds info))
   where
-    details (VanillaInst b _)  = pprLHsBinds b
-    details (NewTypeDerived _) = text "Derived from the representation type"
+    details (VanillaInst b _ _) = pprLHsBinds b
+    details (NewTypeDerived _)  = text "Derived from the representation type"
 
 simpleInstInfoClsTy :: InstInfo a -> (Class, Type)
 simpleInstInfoClsTy info = case instanceHead (iSpec info) of
@@ -678,17 +678,13 @@ name, like otber top-level names, and hence must be made with newGlobalBinder.
 
 \begin{code}
 newDFunName :: Class -> [Type] -> SrcSpan -> TcM Name
-newDFunName clas (ty:_) loc
-  = do { index   <- nextDFunIndex
-       ; is_boot <- tcIsHsBoot
+newDFunName clas tys loc
+  = do { is_boot <- tcIsHsBoot
        ; mod     <- getModule
        ; let info_string = occNameString (getOccName clas) ++ 
-                           occNameString (getDFunTyKey ty)
-             dfun_occ = mkDFunOcc info_string is_boot index
-
+                           concatMap (occNameString.getDFunTyKey) tys
+        ; dfun_occ <- chooseUniqueOccTc (mkDFunOcc info_string is_boot)
        ; newGlobalBinder mod dfun_occ loc }
-
-newDFunName clas [] loc = pprPanic "newDFunName" (ppr clas <+> ppr loc)
 \end{code}
 
 Make a name for the representation tycon of a family instance.  It's an
@@ -696,12 +692,13 @@ Make a name for the representation tycon of a family instance.  It's an
 newGlobalBinder.
 
 \begin{code}
-newFamInstTyConName :: Name -> SrcSpan -> TcM Name
-newFamInstTyConName tc_name loc
-  = do { index <- nextDFunIndex
-       ; mod   <- getModule
-       ; let occ = nameOccName tc_name
-       ; newGlobalBinder mod (mkInstTyTcOcc index occ) loc }
+newFamInstTyConName :: Name -> [Type] -> SrcSpan -> TcM Name
+newFamInstTyConName tc_name tys loc
+  = do { mod   <- getModule
+       ; let info_string = occNameString (getOccName tc_name) ++ 
+                           concatMap (occNameString.getDFunTyKey) tys
+        ; occ   <- chooseUniqueOccTc (mkInstTyTcOcc info_string)
+       ; newGlobalBinder mod occ loc }
 \end{code}
 
 Stable names used for foreign exports and annotations.