From 1eed645c8b03b19a14cf58d9be5317cb81cbd30a Mon Sep 17 00:00:00 2001
From: sheaf <sam.derbyshire@gmail.com>
Date: Tue, 19 Sep 2023 13:10:21 +0200
Subject: [PATCH] Validity: refactor treatment of data families
This commit refactors the reporting of unused type variables in type
and data family instances to be more principled. This avoids ad-hoc
logic in the treatment of data family instances.
---
compiler/GHC/Rename/Module.hs | 9 +-
compiler/GHC/Tc/Errors/Ppr.hs | 59 +++++++-
compiler/GHC/Tc/Errors/Types.hs | 40 +++++-
compiler/GHC/Tc/Validity.hs | 134 +++++++-----------
compiler/GHC/Utils/Outputable.hs | 10 ++
.../should_fail/ExplicitForAllFams4a.stderr | 10 +-
.../should_fail/ExplicitForAllFams4b.stderr | 52 +++----
.../should_fail/SimpleFail13.stderr | 12 ++
.../indexed-types/should_fail/T17008a.stderr | 8 +-
.../indexed-types/should_fail/T7536.stderr | 8 +-
.../tests/typecheck/should_fail/T23734.stderr | 22 +--
.../tests/typecheck/should_fail/T23778.stderr | 4 +-
12 files changed, 221 insertions(+), 147 deletions(-)
diff --git a/compiler/GHC/Rename/Module.hs b/compiler/GHC/Rename/Module.hs
index a13e6a4e70c3..ecf1a3250a41 100644
--- a/compiler/GHC/Rename/Module.hs
+++ b/compiler/GHC/Rename/Module.hs
@@ -71,9 +71,9 @@ import GHC.Core.DataCon ( isSrcStrict )
import Control.Monad
import Control.Arrow ( first )
-import Data.Foldable ( toList )
+import Data.Foldable ( toList, for_ )
import Data.List ( mapAccumL )
-import Data.List.NonEmpty ( NonEmpty(..), head )
+import Data.List.NonEmpty ( NonEmpty(..), head, nonEmpty )
import Data.Maybe ( isNothing, fromMaybe, mapMaybe )
import qualified Data.Set as Set ( difference, fromList, toList, null )
import GHC.Types.GREInfo (ConInfo, mkConInfo, conInfoFields)
@@ -729,9 +729,10 @@ rnFamEqn doc atfi
&& not (cls_tkv `elemNameSet` pat_fvs)
-- ...but not bound on the LHS.
bad_tvs = filter improperly_scoped inst_head_tvs
- ; unless (null bad_tvs) $ addErr $
+ ; for_ (nonEmpty bad_tvs) $ \ ne_bad_tvs ->
+ addErr $
TcRnIllegalInstance $ IllegalFamilyInstance $
- FamInstRHSOutOfScopeTyVars Nothing bad_tvs
+ FamInstRHSOutOfScopeTyVars Nothing ne_bad_tvs
; let eqn_fvs = rhs_fvs `plusFV` pat_fvs
-- See Note [Type family equations and occurrences]
diff --git a/compiler/GHC/Tc/Errors/Ppr.hs b/compiler/GHC/Tc/Errors/Ppr.hs
index 223e2d5bafb5..e6f93b7f3a16 100644
--- a/compiler/GHC/Tc/Errors/Ppr.hs
+++ b/compiler/GHC/Tc/Errors/Ppr.hs
@@ -6181,7 +6181,7 @@ pprIllegalFamilyInstance = \case
hang (text "Mismatched type name in type family instance.")
2 (vcat [ text "Expected:" <+> ppr fam_tc_name
, text " Actual:" <+> ppr eqn_tc_name ])
- FamInstRHSOutOfScopeTyVars mb_dodgy tvs ->
+ FamInstRHSOutOfScopeTyVars mb_dodgy (NE.toList -> tvs) ->
hang (text "Out of scope type variable" <> plural tvs
<+> pprWithCommas (quotes . ppr) tvs
<+> text "in the RHS of a family instance.")
@@ -6194,13 +6194,60 @@ pprIllegalFamilyInstance = \case
mk_extra = case mb_dodgy of
Nothing -> empty
Just (fam_tc, pats, dodgy_tvs) ->
- ppWhen (any (`elemVarSetByKey` dodgy_tvs) (map nameUnique tvs)) $
+ ppWhen (any (`elemVarSetByKey` dodgy_tvs) (fmap nameUnique tvs)) $
hang (text "The real LHS (expanding synonyms) is:")
2 (pprTypeApp fam_tc (map expandTypeSynonyms pats))
- FamInstLHSUnusedBoundTyVars tvs ->
- hang (text "Type variable" <> plural tvs <+> pprQuotedList tvs
- <+> isOrAre tvs <+> text "bound by a forall,")
- 2 (text "but not used in the family instance.")
+ FamInstLHSUnusedBoundTyVars (NE.toList -> bad_qtvs) ->
+ vcat [ not_bound_msg, not_used_msg, dodgy_msg ]
+ where
+
+ -- Filter to only keep user-written variables,
+ -- unless none were user-written in which case we report all of them
+ -- (as we need to report an error).
+ filter_user tvs
+ = map ifiqtv
+ $ case filter ifiqtv_user_written tvs of { [] -> tvs ; qvs -> qvs }
+
+ (not_bound, not_used, dodgy)
+ = case foldr acc_tv ([], [], []) bad_qtvs of
+ (nb, nu, d) -> (filter_user nb, filter_user nu, filter_user d)
+
+ acc_tv tv (nb, nu, d) = case ifiqtv_reason tv of
+ InvalidFamInstQTvNotUsedInRHS -> (nb, tv : nu, d)
+ InvalidFamInstQTvNotBoundInPats -> (tv : nb, nu, d)
+ InvalidFamInstQTvDodgy -> (nb, nu, tv : d)
+
+ -- Error message for type variables not bound in LHS patterns.
+ not_bound_msg
+ | null not_bound
+ = empty
+ | otherwise
+ = vcat [ text "The type variable" <> plural not_bound <+> pprQuotedList not_bound
+ <+> isOrAre not_bound <+> text "bound by a forall,"
+ , text "but" <+> doOrDoes not_bound <+> text "not appear in any of the LHS patterns of the family instance." ]
+
+ -- Error message for type variables bound by a forall but not used
+ -- in the RHS.
+ not_used_msg =
+ if null not_used
+ then empty
+ else text "The type variable" <> plural not_used <+> pprQuotedList not_used
+ <+> isOrAre not_used <+> text "bound by a forall," $$
+ text "but" <+> itOrThey not_used <+>
+ isOrAre not_used <> text "n't used in the family instance."
+
+ -- Error message for dodgy type variables.
+ -- See Note [Dodgy binding sites in type family instances] in GHC.Tc.Validity.
+ dodgy_msg
+ | null dodgy
+ = empty
+ | otherwise
+ = hang (text "Dodgy type variable" <> plural dodgy <+> pprQuotedList dodgy
+ <+> text "in the LHS of a family instance:")
+ 2 (text "the type variable" <> plural dodgy <+> pprQuotedList dodgy
+ <+> text "syntactically appear" <> singular dodgy <+> text "in LHS patterns,"
+ $$ text "but" <+> itOrThey dodgy <+> doOrDoes dodgy <> text "n't appear in an injective position.")
+
illegalFamilyInstanceHints :: IllegalFamilyInstanceReason -> [GhcHint]
illegalFamilyInstanceHints = \case
diff --git a/compiler/GHC/Tc/Errors/Types.hs b/compiler/GHC/Tc/Errors/Types.hs
index 5c77de7b7c1e..9c1f8a2fb879 100644
--- a/compiler/GHC/Tc/Errors/Types.hs
+++ b/compiler/GHC/Tc/Errors/Types.hs
@@ -138,6 +138,7 @@ module GHC.Tc.Errors.Types (
, IllegalHasFieldInstance(..)
, CoverageProblem(..), FailedCoverageCondition(..)
, IllegalFamilyInstanceReason(..)
+ , InvalidFamInstQTv(..), InvalidFamInstQTvReason(..)
, InvalidAssoc(..), InvalidAssocInstance(..)
, InvalidAssocDefault(..), AssocDefaultBadArgs(..)
@@ -181,7 +182,7 @@ import GHC.Types.Avail
import GHC.Types.Hint (UntickedPromotedThing(..))
import GHC.Types.ForeignCall (CLabelString)
import GHC.Types.Id.Info ( RecSelParent(..) )
-import GHC.Types.Name (Name, OccName, getSrcLoc, getSrcSpan)
+import GHC.Types.Name (NamedThing(..), Name, OccName, getSrcLoc, getSrcSpan)
import qualified GHC.Types.Name.Occurrence as OccName
import GHC.Types.Name.Reader
import GHC.Types.SourceFile (HsBootOrSig(..))
@@ -4653,14 +4654,47 @@ data IllegalFamilyInstanceReason
-- ^ family 'TyCon', arguments, and set of "dodgy" type variables
-- See Note [Dodgy binding sites in type family instances]
-- in GHC.Tc.Validity
- ![Name] -- ^ the out-of-scope type variables
+ !(NE.NonEmpty Name) -- ^ the out-of-scope type variables
| FamInstLHSUnusedBoundTyVars
- ![Name] -- ^ the unused bound type variables
+ !(NE.NonEmpty InvalidFamInstQTv) -- ^ the unused bound type variables
| InvalidAssoc !InvalidAssoc
deriving Generic
+-- | A quantified type variable in a type or data family equation that
+-- is either not bound in any LHS patterns or not used in the RHS (or both).
+data InvalidFamInstQTv
+ = InvalidFamInstQTv
+ { ifiqtv :: TcTyVar
+ , ifiqtv_user_written :: Bool
+ -- ^ Did the user write this type variable, or was introduced by GHC?
+ -- For example: with @-XPolyKinds@, in @type instance forall a. F = ()@,
+ -- we have a user-written @a@ but GHC introduces a kind variable @k@
+ -- as well. See #23734.
+ , ifiqtv_reason :: InvalidFamInstQTvReason
+ -- ^ For what reason was the quantified type variable invalid?
+ }
+
+data InvalidFamInstQTvReason
+ -- | A dodgy binder, i.e. a variable that syntactically appears in
+ -- LHS patterns but only in non-injective positions.
+ --
+ -- See Note [Dodgy binding sites in type family instances]
+ -- in GHC.Tc.Validity.
+ = InvalidFamInstQTvDodgy
+ -- | A quantified type variable in a type or data family equation
+ -- that is not bound in any LHS patterns.
+ | InvalidFamInstQTvNotBoundInPats
+ -- | A quantified type variable in a type or data family equation
+ -- that is not used on the RHS.
+ | InvalidFamInstQTvNotUsedInRHS
+
+-- The 'check_tvs' function in 'GHC.Tc.Validity.checkFamPatBinders'
+-- uses 'getSrcSpan', so this 'NamedThing' instance is convenient.
+instance NamedThing InvalidFamInstQTv where
+ getName = getName . ifiqtv
+
data InvalidAssoc
-- | An invalid associated family instance.
--
diff --git a/compiler/GHC/Tc/Validity.hs b/compiler/GHC/Tc/Validity.hs
index b2f7830a52ff..797ee56e6146 100644
--- a/compiler/GHC/Tc/Validity.hs
+++ b/compiler/GHC/Tc/Validity.hs
@@ -47,7 +47,6 @@ import GHC.Core.Unify ( typesAreApart, tcMatchTyX_BM, BindFlag(..) )
import GHC.Core.Coercion
import GHC.Core.Coercion.Axiom
import GHC.Core.Class
-import GHC.Core.DataCon
import GHC.Core.TyCon
import GHC.Core.Predicate
import GHC.Core.TyCo.FVs
@@ -85,6 +84,8 @@ import Control.Monad
import Data.Foldable
import Data.Function
import Data.List ( (\\) )
+import qualified Data.List.NonEmpty as NE
+import Data.List.NonEmpty ( NonEmpty(..) )
{-
************************************************************************
@@ -2164,6 +2165,10 @@ checkValidCoAxiom ax@(CoAxiom { co_ax_tc = fam_tc, co_ax_branches = branches })
-- Check that a "type instance" is well-formed (which includes decidability
-- unless -XUndecidableInstances is given).
--
+-- See also the separate 'checkFamPatBinders' which performs scoping checks
+-- on a type family equation.
+-- (It's separate because it expects 'TyFamEqnValidityInfo', which comes from a
+-- separate place e.g. for associated type defaults.)
checkValidCoAxBranch :: TyCon -> CoAxBranch -> TcM ()
checkValidCoAxBranch fam_tc
(CoAxBranch { cab_lhs = typats
@@ -2174,6 +2179,11 @@ checkValidCoAxBranch fam_tc
-- | Do validity checks on a type family equation, including consistency
-- with any enclosing class instance head, termination, and lack of
-- polytypes.
+--
+-- See also the separate 'checkFamPatBinders' which performs scoping checks
+-- on a type family equation.
+-- (It's separate because it expects 'TyFamEqnValidityInfo', which comes from a
+-- separate place e.g. for associated type defaults.)
checkValidTyFamEqn :: TyCon -- ^ of the type family
-> [Type] -- ^ Type patterns
-> Type -- ^ Rhs
@@ -2297,6 +2307,15 @@ checkTyFamEqnValidityInfo fam_tc = \ case
setSrcSpan loc $
checkFamPatBinders fam_tc qtvs non_user_tvs pats rhs
+-- | Check binders for a type or data family declaration.
+--
+-- Specifically, this function checks for:
+--
+-- - type variables used on the RHS but not bound (explicitly or implicitly)
+-- in the LHS,
+-- - variables bound by a forall in the LHS but not used in the RHS.
+--
+-- See Note [Check type family instance binders].
checkFamPatBinders :: TyCon
-> [TcTyVar] -- ^ Bound on LHS of family instance
-> TyVarSet -- ^ non-user-written tyvars
@@ -2313,7 +2332,7 @@ checkFamPatBinders fam_tc qtvs non_user_tvs pats rhs
, text "cpt_tvs:" <+> ppr cpt_tvs
, text "inj_cpt_tvs:" <+> ppr inj_cpt_tvs
, text "bad_rhs_tvs:" <+> ppr bad_rhs_tvs
- , text "bad_qtvs:" <+> ppr bad_qtvs ]
+ , text "bad_qtvs:" <+> ppr (map ifiqtv bad_qtvs) ]
-- Check for implicitly-bound tyvars, mentioned on the
-- RHS but not bound on the LHS
@@ -2321,36 +2340,18 @@ checkFamPatBinders fam_tc qtvs non_user_tvs pats rhs
-- data family D Int = MkD (forall (a::k). blah)
-- In both cases, 'k' is not bound on the LHS, but is used on the RHS
-- We catch the former in kcDeclHeader, and the latter right here
- -- See Note [Check type-family instance binders]
+ -- See Note [Check type family instance binders]
; check_tvs (FamInstRHSOutOfScopeTyVars (Just (fam_tc, pats, dodgy_tvs)))
- bad_rhs_tvs
+ (map tyVarName bad_rhs_tvs)
-- Check for explicitly forall'd variable that is not bound on LHS
-- data instance forall a. T Int = MkT Int
-- See Note [Unused explicitly bound variables in a family pattern]
- -- See Note [Check type-family instance binders]
+ -- See Note [Check type family instance binders]
; check_tvs FamInstLHSUnusedBoundTyVars bad_qtvs
}
where
- rhs_fvs
- -- Special treatment for data family instances.
- --
- -- See Note [Out of scope tvs in data family instances].
- | Just (tc_rep, _rep_args) <- splitTyConApp_maybe rhs
- , Just (fam_tc', _fam_args, _) <- tyConFamInstSig_maybe tc_rep
- , fam_tc' == fam_tc
- = if isGadtSyntaxTyCon tc_rep
- then emptyFV
- else
- let datacons_fvs =
- unionsFV
- [ delFVs user_tvbs (tyCoFVsOfTypes arg_tys)
- | dc <- tyConDataCons tc_rep
- , let arg_tys = map scaledThing $ dataConOrigArgTys dc
- user_tvbs = mkVarSet $ dataConUserTyVars dc ]
- in datacons_fvs
- | otherwise
- = tyCoFVsOfType rhs
+ rhs_fvs = tyCoFVsOfType rhs
cpt_tvs = tyCoVarsOfTypes pats
inj_cpt_tvs = fvVarSet $ injectiveVarsOfTypes False pats
@@ -2363,71 +2364,40 @@ checkFamPatBinders fam_tc qtvs non_user_tvs pats rhs
-- since the order of `inj_cpt_tvs` is never revealed in an error
-- message.
- used_tvs = cpt_tvs `unionVarSet` fvVarSet rhs_fvs
-
-- Bound but not used at all
- bad_qtvs = filterOut ((`elemVarSet` used_tvs) <||> (`elemVarSet` non_user_tvs))
- qtvs
- -- Filter out non-user-tvs in order to only report user-written type variables,
- -- e.g. type instance forall a. F = ()
- -- -XPolyKinds introduces the binder 'k' for the kind of 'a', but
- -- we don't want the error message to complain about 'k' being unused,
- -- as the user has not written it.
+ bad_qtvs = mapMaybe bad_qtv_maybe qtvs
+
+ bad_qtv_maybe qtv
+ | not_bound_in_pats
+ = let reason
+ | dodgy
+ = InvalidFamInstQTvDodgy
+ | used_in_rhs
+ = InvalidFamInstQTvNotBoundInPats
+ | otherwise
+ = InvalidFamInstQTvNotUsedInRHS
+ in Just $ InvalidFamInstQTv
+ { ifiqtv = qtv
+ , ifiqtv_user_written = not $ qtv `elemVarSet` non_user_tvs
+ , ifiqtv_reason = reason
+ }
+ | otherwise
+ = Nothing
+ where
+ not_bound_in_pats = not $ qtv `elemVarSet` inj_cpt_tvs
+ dodgy = not_bound_in_pats && qtv `elemVarSet` cpt_tvs
+ used_in_rhs = qtv `elemVarSet` fvVarSet rhs_fvs
-- Used on RHS but not bound on LHS
- bad_rhs_tvs = filterOut (`elemVarSet` inj_cpt_tvs) (fvVarList rhs_fvs)
+ bad_rhs_tvs = filterOut ((`elemVarSet` inj_cpt_tvs) <||> (`elem` qtvs)) (fvVarList rhs_fvs)
dodgy_tvs = cpt_tvs `minusVarSet` inj_cpt_tvs
check_tvs mk_err tvs
- = unless (null tvs) $ addErrAt (getSrcSpan (head tvs)) $
+ = for_ (NE.nonEmpty tvs) $ \ ne_tvs@(tv0 :| _) ->
+ addErrAt (getSrcSpan tv0) $
TcRnIllegalInstance $ IllegalFamilyInstance $
- mk_err (map tyVarName tvs)
-
-{- Note [Out of scope tvs in data family instances]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Consider the following data family instance declaration, which we want to reject:
-
- type D :: Type
- data family D
- data instance forall (a :: Type). D = MkD
-
-The problem is that the user quantified the type variable `a` in the instance,
-but didn't use it anywhere.
-
-However, from the perspective of GHC, the RHS of the instance declaration
-is "R:D a", where "R:D" is the representation TyCon that
-GHC.Tc.TyCl.Instance.tcDataFamInstDecl builds; it always includes ALL the
-quantified variables. This means that naively computing the free tyvars of the
-RHS would cause us to report `a` as used on the RHS, which is rather confusing
-for the user (as reported in #23778):
-
- * Type variable `a' is mentioned in the RHS,
- but not bound on the LHS of the family instance
-
-To avoid this, we manually compute which type variables are used on the RHS
-of the data family instance in terms of the types of the data family instance
-constructors:
-
- Vanilla data instance declarations
-
- For a vanilla data declaration, we collect the free type variables of
- the data constructors. For example
-
- data instance D1 x a = K1 a | forall b. K2 a b c
-
- will give rise to RHS FVs {a,c}.
-
- GADT data instance declarations
-
- A GADT data declarations brings its own type variables into scope, e.g.
-
- data instance D3 y b where
- C1 :: ...
- C2 :: ...
-
- So in this case we use emptyFVs for the RHS tyvars.
--}
+ mk_err ne_tvs
-- | Checks that a list of type patterns is valid in a matching (LHS)
-- position of a class instances or type/data family instance.
@@ -2533,7 +2503,7 @@ checkConsistentFamInst (InClsInst { ai_class = clas
| otherwise = BindMe
-{- Note [Check type-family instance binders]
+{- Note [Check type family instance binders]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In a type family instance, we require (of course), type variables
used on the RHS are matched on the LHS. This is checked by
diff --git a/compiler/GHC/Utils/Outputable.hs b/compiler/GHC/Utils/Outputable.hs
index e08b61915c7f..a107d5e1000d 100644
--- a/compiler/GHC/Utils/Outputable.hs
+++ b/compiler/GHC/Utils/Outputable.hs
@@ -52,6 +52,7 @@ module GHC.Utils.Outputable (
ppWhen, ppUnless, ppWhenOption, ppUnlessOption,
speakNth, speakN, speakNOf, plural, singular,
isOrAre, doOrDoes, itsOrTheir, thisOrThese, hasOrHave,
+ itOrThey,
unicodeSyntax,
coloured, keyword,
@@ -1546,6 +1547,15 @@ itsOrTheir :: [a] -> SDoc
itsOrTheir [_] = text "its"
itsOrTheir _ = text "their"
+-- | 'it' or 'they', depeneding on the length of the list.
+--
+-- > itOrThey [x] = text "it"
+-- > itOrThey [x,y] = text "they"
+-- > itOrThey [] = text "they" -- probably avoid this
+itOrThey :: [a] -> SDoc
+itOrThey [_] = text "it"
+itOrThey _ = text "they"
+
-- | Determines the form of subject appropriate for the length of a list:
--
diff --git a/testsuite/tests/indexed-types/should_fail/ExplicitForAllFams4a.stderr b/testsuite/tests/indexed-types/should_fail/ExplicitForAllFams4a.stderr
index 07ed771a220a..8514caa2b2f2 100644
--- a/testsuite/tests/indexed-types/should_fail/ExplicitForAllFams4a.stderr
+++ b/testsuite/tests/indexed-types/should_fail/ExplicitForAllFams4a.stderr
@@ -1,12 +1,12 @@
ExplicitForAllFams4a.hs:8:12: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but it isn't used in the family instance.
• In the equations for closed type family ‘H’
In the type family declaration for ‘H’
-ExplicitForAllFams4a.hs:9:10: error: [GHC-53634]
- • Out of scope type variable ‘b’ in the RHS of a family instance.
- All such variables must be bound on the LHS.
+ExplicitForAllFams4a.hs:9:10: error: [GHC-30337]
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the equations for closed type family ‘H’
In the type family declaration for ‘H’
diff --git a/testsuite/tests/indexed-types/should_fail/ExplicitForAllFams4b.stderr b/testsuite/tests/indexed-types/should_fail/ExplicitForAllFams4b.stderr
index 80bc9138403a..03c9d499ed78 100644
--- a/testsuite/tests/indexed-types/should_fail/ExplicitForAllFams4b.stderr
+++ b/testsuite/tests/indexed-types/should_fail/ExplicitForAllFams4b.stderr
@@ -1,7 +1,7 @@
ExplicitForAllFams4b.hs:8:24: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but it isn't used in the family instance.
• In the type instance declaration for ‘J’
ExplicitForAllFams4b.hs:8:27: error: [GHC-34447]
@@ -9,14 +9,14 @@ ExplicitForAllFams4b.hs:8:27: error: [GHC-34447]
J [a] = Float -- Defined at ExplicitForAllFams4b.hs:8:27
J _ = Maybe b -- Defined at ExplicitForAllFams4b.hs:9:27
-ExplicitForAllFams4b.hs:9:22: error: [GHC-53634]
- • Out of scope type variable ‘b’ in the RHS of a family instance.
- All such variables must be bound on the LHS.
+ExplicitForAllFams4b.hs:9:22: error: [GHC-30337]
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the type instance declaration for ‘J’
ExplicitForAllFams4b.hs:12:24: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the data instance declaration for ‘K’
ExplicitForAllFams4b.hs:12:27: error: [GHC-34447]
@@ -25,13 +25,13 @@ ExplicitForAllFams4b.hs:12:27: error: [GHC-34447]
K _ -- Defined at ExplicitForAllFams4b.hs:13:27
ExplicitForAllFams4b.hs:13:22: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the data instance declaration for ‘K’
ExplicitForAllFams4b.hs:16:27: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the newtype instance declaration for ‘L’
ExplicitForAllFams4b.hs:16:30: error: [GHC-34447]
@@ -40,8 +40,8 @@ ExplicitForAllFams4b.hs:16:30: error: [GHC-34447]
L _ -- Defined at ExplicitForAllFams4b.hs:17:30
ExplicitForAllFams4b.hs:17:25: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the newtype instance declaration for ‘L’
ExplicitForAllFams4b.hs:24:3: error: [GHC-95424]
@@ -52,8 +52,8 @@ ExplicitForAllFams4b.hs:24:3: error: [GHC-95424]
In the instance declaration for ‘C Int’
ExplicitForAllFams4b.hs:24:17: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but it isn't used in the family instance.
• In the type instance declaration for ‘CT’
In the instance declaration for ‘C Int’
@@ -65,31 +65,31 @@ ExplicitForAllFams4b.hs:25:3: error: [GHC-95424]
In the instance declaration for ‘C Int’
ExplicitForAllFams4b.hs:25:17: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the data instance declaration for ‘CD’
In the instance declaration for ‘C Int’
-ExplicitForAllFams4b.hs:28:15: error: [GHC-53634]
- • Out of scope type variable ‘b’ in the RHS of a family instance.
- All such variables must be bound on the LHS.
+ExplicitForAllFams4b.hs:28:15: error: [GHC-30337]
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the type instance declaration for ‘CT’
In the instance declaration for ‘C Bool’
ExplicitForAllFams4b.hs:29:15: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the data instance declaration for ‘CD’
In the instance declaration for ‘C Bool’
ExplicitForAllFams4b.hs:32:15: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but it isn't used in the family instance.
• In the type instance declaration for ‘CT’
In the instance declaration for ‘C Double’
ExplicitForAllFams4b.hs:33:15: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘b’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the data instance declaration for ‘CD’
In the instance declaration for ‘C Double’
diff --git a/testsuite/tests/indexed-types/should_fail/SimpleFail13.stderr b/testsuite/tests/indexed-types/should_fail/SimpleFail13.stderr
index f110a9dbe1c5..933fdc41f672 100644
--- a/testsuite/tests/indexed-types/should_fail/SimpleFail13.stderr
+++ b/testsuite/tests/indexed-types/should_fail/SimpleFail13.stderr
@@ -4,7 +4,19 @@ SimpleFail13.hs:9:15: error: [GHC-73138]
D [C a]
• In the data instance declaration for ‘D’
+SimpleFail13.hs:9:17: error: [GHC-30337]
+ • Dodgy type variable ‘a’ in the LHS of a family instance:
+ the type variable ‘a’ syntactically appears in LHS patterns,
+ but it doesn't appear in an injective position.
+ • In the data instance declaration for ‘D’
+
SimpleFail13.hs:13:15: error: [GHC-73138]
• Illegal type synonym family application ‘C a’ in instance:
E [C a]
• In the type instance declaration for ‘E’
+
+SimpleFail13.hs:13:17: error: [GHC-30337]
+ • Dodgy type variable ‘a’ in the LHS of a family instance:
+ the type variable ‘a’ syntactically appears in LHS patterns,
+ but it doesn't appear in an injective position.
+ • In the type instance declaration for ‘E’
diff --git a/testsuite/tests/indexed-types/should_fail/T17008a.stderr b/testsuite/tests/indexed-types/should_fail/T17008a.stderr
index 600857e641f2..59b9a6dd8468 100644
--- a/testsuite/tests/indexed-types/should_fail/T17008a.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T17008a.stderr
@@ -1,7 +1,7 @@
-T17008a.hs:12:5: error: [GHC-53634]
- • Out of scope type variable ‘a’ in the RHS of a family instance.
- All such variables must be bound on the LHS.
- The real LHS (expanding synonyms) is: F @a x
+T17008a.hs:12:5: error: [GHC-30337]
+ • Dodgy type variable ‘a’ in the LHS of a family instance:
+ the type variable ‘a’ syntactically appears in LHS patterns,
+ but it doesn't appear in an injective position.
• In the equations for closed type family ‘F’
In the type family declaration for ‘F’
diff --git a/testsuite/tests/indexed-types/should_fail/T7536.stderr b/testsuite/tests/indexed-types/should_fail/T7536.stderr
index 557160f8a99a..73ebebc93e10 100644
--- a/testsuite/tests/indexed-types/should_fail/T7536.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T7536.stderr
@@ -1,6 +1,6 @@
-T7536.hs:8:18: error: [GHC-53634]
- • Out of scope type variable ‘a’ in the RHS of a family instance.
- All such variables must be bound on the LHS.
- The real LHS (expanding synonyms) is: TF Int
+T7536.hs:8:18: error: [GHC-30337]
+ • Dodgy type variable ‘a’ in the LHS of a family instance:
+ the type variable ‘a’ syntactically appears in LHS patterns,
+ but it doesn't appear in an injective position.
• In the type instance declaration for ‘TF’
diff --git a/testsuite/tests/typecheck/should_fail/T23734.stderr b/testsuite/tests/typecheck/should_fail/T23734.stderr
index b5ffbca9fd02..1826957bf2f4 100644
--- a/testsuite/tests/typecheck/should_fail/T23734.stderr
+++ b/testsuite/tests/typecheck/should_fail/T23734.stderr
@@ -1,22 +1,22 @@
-T23734.hs:7:22: error: [GHC-30337]
- • Type variable ‘a’ is bound by a forall,
- but not used in the family instance.
+T23734.hs:7:25: error: [GHC-30337]
+ • The type variable ‘a’ is bound by a forall,
+ but it isn't used in the family instance.
• In the type instance declaration for ‘F’
-T23734.hs:10:10: error: [GHC-30337]
- • Type variable ‘b’ is bound by a forall,
- but not used in the family instance.
+T23734.hs:10:3: error: [GHC-30337]
+ • The type variable ‘b’ is bound by a forall,
+ but it isn't used in the family instance.
• In the equations for closed type family ‘G’
In the type family declaration for ‘G’
-T23734.hs:14:15: error: [GHC-30337]
- • Type variable ‘c’ is bound by a forall,
- but not used in the family instance.
+T23734.hs:14:3: error: [GHC-30337]
+ • The type variable ‘c’ is bound by a forall,
+ but it isn't used in the family instance.
• In the default type instance declaration for ‘H’
In the class declaration for ‘C’
T23734.hs:17:23: error: [GHC-30337]
- • Type variable ‘d’ is bound by a forall,
- but not used in the family instance.
+ • The type variable ‘d’ is bound by a forall,
+ but does not appear in any of the LHS patterns of the family instance.
• In the data instance declaration for ‘D’
diff --git a/testsuite/tests/typecheck/should_fail/T23778.stderr b/testsuite/tests/typecheck/should_fail/T23778.stderr
index 1faf580c1896..429f6c299f48 100644
--- a/testsuite/tests/typecheck/should_fail/T23778.stderr
+++ b/testsuite/tests/typecheck/should_fail/T23778.stderr
@@ -1,5 +1,5 @@
T23778.hs:7:22: error: [GHC-30337]
- • Type variables ‘d’, ‘v’ are bound by a forall,
- but not used in the family instance.
+ • The type variables ‘d’, ‘v’ are bound by a forall,
+ but do not appear in any of the LHS patterns of the family instance.
• In the data instance declaration for ‘D’
--
GitLab