when the dict is constructed in TcInstDcls.tcInstDecl2
-
+Note [Unused constructors and deriving clauses]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+See Trac #3221. Consider
+ data T = T1 | T2 deriving( Show )
+Are T1 and T2 unused? Well, no: the deriving clause expands to mention
+both of them. So we gather defs/uses from deriving just like anything else.
%************************************************************************
%* *
-> [LInstDecl Name] -- All instance declarations
-> [LDerivDecl Name] -- All stand-alone deriving declarations
-> TcM ([InstInfo Name], -- The generated "instance decls"
- HsValBinds Name) -- Extra generated top-level bindings
+ HsValBinds Name, -- Extra generated top-level bindings
+ DefUses)
tcDeriving tycl_decls inst_decls deriv_decls
- = recoverM (return ([], emptyValBindsOut)) $
+ = recoverM (return ([], emptyValBindsOut, emptyDUs)) $
do { -- Fish the "deriving"-related information out of the TcEnv
-- And make the necessary "equations".
is_boot <- tcIsHsBoot
-- Generate the generic to/from functions from each type declaration
; gen_binds <- mkGenericBinds is_boot
- ; (inst_info, rn_binds) <- renameDeriv is_boot gen_binds (insts1 ++ insts2)
+ ; (inst_info, rn_binds, rn_dus) <- renameDeriv is_boot gen_binds (insts1 ++ insts2)
; dflags <- getDOpts
; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
(ddump_deriving inst_info rn_binds))
- ; return (inst_info, rn_binds) }
+ ; return (inst_info, rn_binds, rn_dus) }
where
ddump_deriving :: [InstInfo Name] -> HsValBinds Name -> SDoc
ddump_deriving inst_infos extra_binds
renameDeriv :: Bool -> LHsBinds RdrName
-> [(InstInfo RdrName, DerivAuxBinds)]
- -> TcM ([InstInfo Name], HsValBinds Name)
+ -> TcM ([InstInfo Name], HsValBinds Name, DefUses)
renameDeriv is_boot gen_binds insts
| is_boot -- If we are compiling a hs-boot file, don't generate any derived bindings
-- The inst-info bindings will all be empty, but it's easier to
-- just use rn_inst_info to change the type appropriately
- = do { rn_inst_infos <- mapM rn_inst_info inst_infos
- ; return (rn_inst_infos, emptyValBindsOut) }
+ = do { (rn_inst_infos, fvs) <- mapAndUnzipM rn_inst_info inst_infos
+ ; return (rn_inst_infos, emptyValBindsOut, usesOnly (plusFVs fvs)) }
| otherwise
= discardWarnings $ -- Discard warnings about unused bindings etc
; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs)
; bindLocalNames aux_names $
- do { (rn_aux, _dus) <- rnTopBindsRHS (mkNameSet aux_names) rn_aux_lhs
- ; rn_inst_infos <- mapM rn_inst_info inst_infos
- ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen) } }
+ do { (rn_aux, dus_aux) <- rnTopBindsRHS (mkNameSet aux_names) rn_aux_lhs
+ ; (rn_inst_infos, fvs_insts) <- mapAndUnzipM rn_inst_info inst_infos
+ ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen,
+ dus_gen `plusDU` dus_aux `plusDU` usesOnly (plusFVs fvs_insts)) } }
where
(inst_infos, deriv_aux_binds) = unzip insts
rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived co })
- = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived co })
+ = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived co }, emptyFVs)
rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs })
= -- Bring the right type variables into
-- scope (yuk), and rename the method binds
ASSERT( null sigs )
bindLocalNames (map Var.varName tyvars) $
- do { (rn_binds, _fvs) <- rnMethodBinds clas_nm (\_ -> []) [] binds
- ; return (InstInfo { iSpec = inst, iBinds = VanillaInst rn_binds [] }) }
+ do { (rn_binds, fvs) <- rnMethodBinds clas_nm (\_ -> []) [] binds
+ ; return (InstInfo { iSpec = inst, iBinds = VanillaInst rn_binds [] }, fvs) }
where
(tyvars,_,clas,_) = instanceHead inst
clas_nm = className clas
| cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration)
| cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct)
| cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct)
- | cls_key == dataClassKey = Just (cond_mayDeriveDataTypeable `andCond` cond_std `andCond` cond_noUnliftedArgs)
- | cls_key == functorClassKey = Just (cond_std `andCond` cond_functorOK True)
- | cls_key == foldableClassKey = Just (cond_std `andCond` cond_functorOK False)
- | cls_key == traversableClassKey = Just (cond_std `andCond` cond_functorOK False)
- | getName cls `elem` typeableClassNames = Just (cond_mayDeriveDataTypeable `andCond` cond_typeableOK)
+ | cls_key == dataClassKey = Just (checkFlag Opt_DeriveDataTypeable `andCond`
+ cond_std `andCond` cond_noUnliftedArgs)
+ | cls_key == functorClassKey = Just (checkFlag Opt_DeriveFunctor `andCond`
+ cond_functorOK True) -- NB: no cond_std!
+ | cls_key == foldableClassKey = Just (checkFlag Opt_DeriveFoldable `andCond`
+ cond_functorOK False) -- Functor/Fold/Trav works ok for rank-n types
+ | cls_key == traversableClassKey = Just (checkFlag Opt_DeriveTraversable `andCond`
+ cond_functorOK False)
+ | getName cls `elem` typeableClassNames = Just (checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK)
| otherwise = Nothing
where
cls_key = getUnique cls
cond_std :: Condition
cond_std (_, rep_tc)
- | any (not . isVanillaDataCon) data_cons = Just existential_why
- | null data_cons = Just no_cons_why
- | otherwise = Nothing
+ | null data_cons = Just no_cons_why
+ | not (null con_whys) = Just (vcat con_whys)
+ | otherwise = Nothing
where
data_cons = tyConDataCons rep_tc
no_cons_why = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "has no data constructors")
- existential_why = quotes (pprSourceTyCon rep_tc) <+>
- ptext (sLit "has non-Haskell-98 constructor(s)")
+
+ con_whys = mapCatMaybes check_con data_cons
+
+ check_con :: DataCon -> Maybe SDoc
+ check_con con
+ | isVanillaDataCon con
+ , all isTauTy (dataConOrigArgTys con) = Nothing
+ | otherwise = Just (badCon con (ptext (sLit "does not have a Haskell-98 type")))
cond_enumOrProduct :: Condition
cond_enumOrProduct = cond_isEnumeration `orCond`
where
bad_cons = [ con | con <- tyConDataCons tc
, any isUnLiftedType (dataConOrigArgTys con) ]
- why = ptext (sLit "Constructor") <+> quotes (ppr (head bad_cons))
- <+> ptext (sLit "has arguments of unlifted type")
+ why = badCon (head bad_cons) (ptext (sLit "has arguments of unlifted type"))
cond_isEnumeration :: Condition
cond_isEnumeration (_, rep_tc)
= msum (map check_con data_cons) -- msum picks the first 'Just', if any
where
data_cons = tyConDataCons rep_tc
- check_con con = msum (foldDataConArgs ft_check con)
-
- ft_check :: FFoldType (Maybe SDoc)
- ft_check = FT { ft_triv = Nothing, ft_var = Nothing, ft_co_var = Just covariant
- , ft_fun = \x y -> if allowFunctions then x `mplus` y else Just functions
- , ft_tup = \_ xs -> msum xs
- , ft_ty_app = \_ x -> x
- , ft_bad_app = Just wrong_arg
- , ft_forall = \_ x -> x }
+ check_con con = msum (check_vanilla con : foldDataConArgs (ft_check con) con)
+
+ check_vanilla :: DataCon -> Maybe SDoc
+ check_vanilla con | isVanillaDataCon con = Nothing
+ | otherwise = Just (badCon con existential)
+
+ ft_check :: DataCon -> FFoldType (Maybe SDoc)
+ ft_check con = FT { ft_triv = Nothing, ft_var = Nothing
+ , ft_co_var = Just (badCon con covariant)
+ , ft_fun = \x y -> if allowFunctions then x `mplus` y
+ else Just (badCon con functions)
+ , ft_tup = \_ xs -> msum xs
+ , ft_ty_app = \_ x -> x
+ , ft_bad_app = Just (badCon con wrong_arg)
+ , ft_forall = \_ x -> x }
- covariant = quotes (pprSourceTyCon rep_tc) <+>
- ptext (sLit "uses the type variable in a function argument")
- functions = quotes (pprSourceTyCon rep_tc) <+>
- ptext (sLit "contains function types")
- wrong_arg = quotes (pprSourceTyCon rep_tc) <+>
- ptext (sLit "uses the type variable in an argument other than the last")
-
-cond_mayDeriveDataTypeable :: Condition
-cond_mayDeriveDataTypeable (dflags, _)
- | dopt Opt_DeriveDataTypeable dflags = Nothing
- | otherwise = Just why
+ existential = ptext (sLit "has existential arguments")
+ covariant = ptext (sLit "uses the type variable in a function argument")
+ functions = ptext (sLit "contains function types")
+ wrong_arg = ptext (sLit "uses the type variable in an argument other than the last")
+
+checkFlag :: DynFlag -> Condition
+checkFlag flag (dflags, _)
+ | dopt flag dflags = Nothing
+ | otherwise = Just why
where
- why = ptext (sLit "You need -XDeriveDataTypeable to derive an instance for this class")
+ why = ptext (sLit "You need -X") <> text flag_str
+ <+> ptext (sLit "to derive an instance for this class")
+ flag_str = case [ s | (s, f, _) <- xFlags, f==flag ] of
+ [s] -> s
+ other -> pprPanic "checkFlag" (ppr other)
std_class_via_iso :: Class -> Bool
std_class_via_iso clas -- These standard classes can be derived for a newtype
; newDFunName clas [mkTyConApp tycon []] loc }
-- The type passed to newDFunName is only used to generate
-- a suitable string; hence the empty type arg list
+
+badCon :: DataCon -> SDoc -> SDoc
+badCon con msg = ptext (sLit "Constructor") <+> quotes (ppr con) <+> msg
\end{code}
Note [Superclasses of derived instance]