diff options
| -rw-r--r-- | compiler/main/DynFlags.hs | 3 | ||||
| -rw-r--r-- | compiler/rename/RnTypes.hs | 15 | ||||
| -rw-r--r-- | docs/users_guide/8.6.1-notes.rst | 6 | ||||
| -rw-r--r-- | docs/users_guide/using-warnings.rst | 53 | ||||
| -rw-r--r-- | libraries/base/Data/Typeable/Internal.hs | 9 | ||||
| -rw-r--r-- | testsuite/tests/dependent/should_compile/T15264.hs | 15 | ||||
| -rw-r--r-- | testsuite/tests/dependent/should_compile/T15264.stderr | 10 | ||||
| -rw-r--r-- | testsuite/tests/dependent/should_compile/all.T | 1 |
8 files changed, 108 insertions, 4 deletions
diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs index 437afc33a7..485eb72942 100644 --- a/compiler/main/DynFlags.hs +++ b/compiler/main/DynFlags.hs @@ -807,6 +807,7 @@ data WarningFlag = | Opt_WarnMissingExportList | Opt_WarnInaccessibleCode | Opt_WarnStarIsType -- Since 8.6 + | Opt_WarnImplicitKindVars -- Since 8.6 deriving (Eq, Show, Enum) data Language = Haskell98 | Haskell2010 @@ -3784,6 +3785,7 @@ wWarningFlagsDeps = [ flagSpec "hi-shadowing" Opt_WarnHiShadows, flagSpec "inaccessible-code" Opt_WarnInaccessibleCode, flagSpec "implicit-prelude" Opt_WarnImplicitPrelude, + flagSpec "implicit-kind-vars" Opt_WarnImplicitKindVars, flagSpec "incomplete-patterns" Opt_WarnIncompletePatterns, flagSpec "incomplete-record-updates" Opt_WarnIncompletePatternsRecUpd, flagSpec "incomplete-uni-patterns" Opt_WarnIncompleteUniPatterns, @@ -4593,6 +4595,7 @@ minusWcompatOpts = [ Opt_WarnMissingMonadFailInstances , Opt_WarnSemigroup , Opt_WarnNonCanonicalMonoidInstances + , Opt_WarnImplicitKindVars ] enableUnusedBinds :: DynP () diff --git a/compiler/rename/RnTypes.hs b/compiler/rename/RnTypes.hs index 3d60a9f6c3..ca4986f050 100644 --- a/compiler/rename/RnTypes.hs +++ b/compiler/rename/RnTypes.hs @@ -334,6 +334,11 @@ rnImplicitBndrs bind_free_tvs ; traceRn "rnImplicitBndrs" (vcat [ ppr kvs, ppr tvs, ppr real_tvs ]) + ; whenWOptM Opt_WarnImplicitKindVars $ + unless (bind_free_tvs || null kvs) $ + addWarnAt (Reason Opt_WarnImplicitKindVars) (getLoc (head kvs)) $ + implicit_kind_vars_msg kvs + ; loc <- getSrcSpanM ; vars <- mapM (newLocalBndrRn . L loc . unLoc) (kvs ++ real_tvs) @@ -343,6 +348,16 @@ rnImplicitBndrs bind_free_tvs ; bindLocalNamesFV vars $ thing_inside vars } + where + implicit_kind_vars_msg kvs = + vcat [ text "An explicit" <+> quotes (text "forall") <+> + text "was used, but the following kind variables" <+> + text "are not quantified:" <+> + hsep (punctuate comma (map (quotes . ppr) kvs)) + , text "Despite this fact, GHC will introduce them into scope," <+> + text "but it will stop doing so in the future." + , text "Suggested fix: add" <+> + quotes (text "forall" <+> hsep (map ppr kvs) <> char '.') ] rnLHsInstType :: SDoc -> LHsSigType GhcPs -> RnM (LHsSigType GhcRn, FreeVars) -- Rename the type in an instance. diff --git a/docs/users_guide/8.6.1-notes.rst b/docs/users_guide/8.6.1-notes.rst index 4bc01c904e..5b13909401 100644 --- a/docs/users_guide/8.6.1-notes.rst +++ b/docs/users_guide/8.6.1-notes.rst @@ -152,6 +152,12 @@ Compiler :ghc-flag:`-fexternal-dynamic-refs`. If you don't know why you might need this, you don't need it. +- :ghc-flag:`-Wcompat` now includes :ghc-flag:`-Wimplicit-kind-vars` to + provide early detection of breakage that will be caused by implementation of + `GHC proposal #24 + <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0024-no-kind-vars.rst>`__ + in a future release. + Plugins ~~~~~~~ diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst index 87ddcdabf7..7dc4a3b048 100644 --- a/docs/users_guide/using-warnings.rst +++ b/docs/users_guide/using-warnings.rst @@ -109,6 +109,7 @@ The following flags are simple ways to select standard "packages" of warnings: * :ghc-flag:`-Wmissing-monadfail-instances` * :ghc-flag:`-Wsemigroup` * :ghc-flag:`-Wnoncanonical-monoid-instances` + * :ghc-flag:`-Wimplicit-kind-vars` .. ghc-flag:: -Wno-compat :shortdesc: Disables all warnings enabled by :ghc-flag:`-Wcompat`. @@ -768,6 +769,58 @@ of ``-W(no-)*``. This warning is off by default. +.. ghc-flag:: -Wimplicit-kind-vars + :shortdesc: warn when kind variables are brought into scope implicitly despite + the "forall-or-nothing" rule + :type: dynamic + :reverse: -Wno-implicit-kind-vars + :category: + + :since: 8.6 + + `GHC proposal #24 + <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0024-no-kind-vars.rst>`__ + prescribes to treat kind variables and type variables identically in + ``forall``, removing the legacy distinction between them. + + Consider the following examples: :: + + f :: Proxy a -> Proxy b -> () + g :: forall a b. Proxy a -> Proxy b -> () + + ``f`` does not use an explicit ``forall``, so type variables ``a`` and ``b`` + are brought into scope implicitly. ``g`` quantifies both ``a`` and ``b`` + explicitly. Both ``f`` and ``g`` work today and will continue to work in the + future because they adhere to the "forall-or-nothing" rule: either all type + variables in a function definition are introduced explicitly or implicitly, + there is no middle ground. + + A violation of the "forall-or-nothing" rule looks like this: :: + + m :: forall a. Proxy a -> Proxy b -> () + + ``m`` does not introduce one of the variables, ``b``, and thus is rejected. + + However, consider the following example: :: + + n :: forall a. Proxy (a :: k) -> () + + While ``n`` uses ``k`` without introducing it and thus violates the rule, it + is currently accepted. This is because ``k`` in ``n`` is considered a kind + variable, as it occurs in a kind signature. In reality, the line between + type variables and kind variables is blurry, as the following example + demonstrates: :: + + kindOf :: forall a. Proxy (a :: k) -> Proxy k + + In ``kindOf``, the ``k`` variable is used both in a kind position and a type + position. Currently, ``kindOf`` happens to be accepted as well. + + In a future release of GHC, both ``n`` and ``kindOf`` will be rejected per + the "forall-or-nothing" rule. This warning, being part of the + :ghc-flag:`-Wcompat` option group, allows to detect this before the actual + breaking change takes place. + .. ghc-flag:: -Wincomplete-patterns :shortdesc: warn when a pattern match could fail :type: dynamic diff --git a/libraries/base/Data/Typeable/Internal.hs b/libraries/base/Data/Typeable/Internal.hs index 09290485e4..0d4fc825cf 100644 --- a/libraries/base/Data/Typeable/Internal.hs +++ b/libraries/base/Data/Typeable/Internal.hs @@ -476,7 +476,7 @@ splitApp (TrTyCon{trTyCon = con, trKindVars = kinds}) Refl -> IsCon con kinds -- | Use a 'TypeRep' as 'Typeable' evidence. -withTypeable :: forall (a :: k) (r :: TYPE rep). () +withTypeable :: forall k (a :: k) rep (r :: TYPE rep). () => TypeRep a -> (Typeable a => r) -> r withTypeable rep k = unsafeCoerce k' rep where k' :: Gift a r @@ -631,7 +631,7 @@ unkindedTypeRep :: SomeKindedTypeRep k -> SomeTypeRep unkindedTypeRep (SomeKindedTypeRep x) = SomeTypeRep x data SomeKindedTypeRep k where - SomeKindedTypeRep :: forall (a :: k). TypeRep a + SomeKindedTypeRep :: forall k (a :: k). TypeRep a -> SomeKindedTypeRep k kApp :: SomeKindedTypeRep (k -> k') @@ -640,7 +640,7 @@ kApp :: SomeKindedTypeRep (k -> k') kApp (SomeKindedTypeRep f) (SomeKindedTypeRep a) = SomeKindedTypeRep (mkTrApp f a) -kindedTypeRep :: forall (a :: k). Typeable a => SomeKindedTypeRep k +kindedTypeRep :: forall k (a :: k). Typeable a => SomeKindedTypeRep k kindedTypeRep = SomeKindedTypeRep (typeRep @a) buildList :: forall k. Typeable k @@ -980,7 +980,8 @@ tcNat :: TyCon tcNat = typeRepTyCon (typeRep @Nat) -- | An internal function, to make representations for type literals. -typeLitTypeRep :: forall (a :: k). (Typeable k) => String -> TyCon -> TypeRep a +typeLitTypeRep :: forall k (a :: k). (Typeable k) => + String -> TyCon -> TypeRep a typeLitTypeRep nm kind_tycon = mkTrCon (mkTypeLitTyCon nm kind_tycon) [] -- | For compiler use. diff --git a/testsuite/tests/dependent/should_compile/T15264.hs b/testsuite/tests/dependent/should_compile/T15264.hs new file mode 100644 index 0000000000..a03cf4346e --- /dev/null +++ b/testsuite/tests/dependent/should_compile/T15264.hs @@ -0,0 +1,15 @@ +{-# LANGUAGE ExplicitForAll, PolyKinds #-} +{-# OPTIONS -Wcompat #-} + +module T15264 where + +import Data.Proxy + +bad1 :: forall (a :: k). Proxy a -> () +bad1 _ = () + +bad2 :: forall (a :: k1) (b :: k2). Proxy a -> () +bad2 _ = () + +good :: forall k (a :: k). Proxy a -> () +good _ = () diff --git a/testsuite/tests/dependent/should_compile/T15264.stderr b/testsuite/tests/dependent/should_compile/T15264.stderr new file mode 100644 index 0000000000..222d686513 --- /dev/null +++ b/testsuite/tests/dependent/should_compile/T15264.stderr @@ -0,0 +1,10 @@ + +T15264.hs:8:22: warning: [-Wimplicit-kind-vars (in -Wcompat)] + An explicit ‘forall’ was used, but the following kind variables are not quantified: ‘k’ + Despite this fact, GHC will introduce them into scope, but it will stop doing so in the future. + Suggested fix: add ‘forall k.’ + +T15264.hs:11:22: warning: [-Wimplicit-kind-vars (in -Wcompat)] + An explicit ‘forall’ was used, but the following kind variables are not quantified: ‘k1’, ‘k2’ + Despite this fact, GHC will introduce them into scope, but it will stop doing so in the future. + Suggested fix: add ‘forall k1 k2.’ diff --git a/testsuite/tests/dependent/should_compile/all.T b/testsuite/tests/dependent/should_compile/all.T index 40ba2110f9..2865351ff5 100644 --- a/testsuite/tests/dependent/should_compile/all.T +++ b/testsuite/tests/dependent/should_compile/all.T @@ -48,4 +48,5 @@ test('T14720', normal, compile, ['']) test('T14066a', normal, compile, ['']) test('T14749', normal, compile, ['']) test('T14991', normal, compile, ['']) +test('T15264', normal, compile, ['']) test('DkNameRes', normal, compile, [''])
\ No newline at end of file |