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-rw-r--r--compiler/simplCore/OccurAnal.hs23
-rw-r--r--testsuite/tests/patsyn/should_fail/T15695.hs48
-rw-r--r--testsuite/tests/patsyn/should_fail/T15695.stderr45
-rw-r--r--testsuite/tests/patsyn/should_fail/all.T1
4 files changed, 117 insertions, 0 deletions
diff --git a/compiler/simplCore/OccurAnal.hs b/compiler/simplCore/OccurAnal.hs
index 236bb81066..2cc38a27e0 100644
--- a/compiler/simplCore/OccurAnal.hs
+++ b/compiler/simplCore/OccurAnal.hs
@@ -2501,6 +2501,10 @@ zapDetails = markAllMany . markAllNonTailCalled -- effectively sets to noOccInfo
lookupDetails :: UsageDetails -> Id -> OccInfo
lookupDetails ud id
+ | isCoVar id -- We do not currenly gather occurrence info (from types)
+ = noOccInfo -- for CoVars, so we must conservatively mark them as used
+ -- See Note [DoO not mark CoVars as dead]
+ | otherwise
= case lookupVarEnv (ud_env ud) id of
Just occ -> doZapping ud id occ
Nothing -> IAmDead
@@ -2512,6 +2516,25 @@ udFreeVars :: VarSet -> UsageDetails -> VarSet
-- Find the subset of bndrs that are mentioned in uds
udFreeVars bndrs ud = restrictUniqSetToUFM bndrs (ud_env ud)
+{- Note [Do not mark CoVars as dead]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It's obviously wrong to mark CoVars as dead if they are used.
+Currently we don't traverse types to gather usase info for CoVars,
+so we had better treat them as having noOccInfo.
+
+This showed up in Trac #15696 we had something like
+ case eq_sel d of co -> ...(typeError @(...co...) "urk")...
+
+Then 'd' was substitued by a dictionary, so the expression
+simpified to
+ case (Coercion <blah>) of co -> ...(typeError @(...co...) "urk")...
+
+But then the "drop the case altogether" equation of rebuildCase
+thought that 'co' was dead, and discarded the entire case. Urk!
+
+I have no idea how we managed to avoid this pitfall for so long!
+-}
+
-------------------
-- Auxiliary functions for UsageDetails implementation
diff --git a/testsuite/tests/patsyn/should_fail/T15695.hs b/testsuite/tests/patsyn/should_fail/T15695.hs
new file mode 100644
index 0000000000..de8035c728
--- /dev/null
+++ b/testsuite/tests/patsyn/should_fail/T15695.hs
@@ -0,0 +1,48 @@
+{-# Language RankNTypes, PatternSynonyms, DataKinds, PolyKinds, GADTs,
+ TypeOperators, MultiParamTypeClasses, TypeFamilies,
+ TypeSynonymInstances, FlexibleInstances, InstanceSigs, FlexibleContexts #-}
+
+{-# Options_GHC -fdefer-type-errors #-}
+
+module T15695 where
+
+import Data.Kind
+import Data.Type.Equality
+
+data TyVar :: Type -> Type -> Type where
+ VO :: TyVar (a -> as) a
+ VS :: TyVar as a -> TyVar (b -> as) a
+
+data NP :: (k -> Type) -> ([k] -> Type) where
+ Nil :: NP f '[]
+ (:*) :: f a -> NP f as -> NP f (a:as)
+
+data NS :: (k -> Type) -> ([k] -> Type) where
+ Here :: f a -> NS f (a:as)
+ There :: NS f as -> NS f (a:as)
+
+infixr 6 :&:
+data Ctx :: Type -> Type where
+ E :: Ctx(Type)
+ (:&:) :: a -> Ctx(as) -> Ctx(a -> as)
+
+data NA a
+
+type SOP(kind::Type) code = NS (NP NA) code
+
+data ApplyT(kind::Type) :: kind -> Ctx(kind) -> Type where
+ AO :: a -> ApplyT(Type) a E
+ AS :: ApplyT(ks) (f a) ctx
+ -> ApplyT(k -> ks) f (a:&:ctx)
+
+from' :: ApplyT(Type -> Type -> Type) Either ctx -> NS (NP NA) '[ '[VO] ]
+from' (ASSO (Left a)) = Here (a :* Nil)
+from' (ASSO (Right b)) = There (Here undefined)
+
+pattern ASSO
+ :: () =>
+ forall (ks :: Type) k (f :: k -> ks) (a1 :: k) (ks1 :: Type) k1 (f1 :: k1 -> ks1) (a2 :: k1) a3.
+ (kind ~ (k -> k1 -> Type), a ~~ f, b ~~ (a1 :&: a2 :&: E),
+ f a1 ~~ f1, f1 a2 ~~ a3) =>
+ a3 -> ApplyT kind a b
+pattern ASSO a = AS (AS (AO a))
diff --git a/testsuite/tests/patsyn/should_fail/T15695.stderr b/testsuite/tests/patsyn/should_fail/T15695.stderr
new file mode 100644
index 0000000000..6ef415ad9b
--- /dev/null
+++ b/testsuite/tests/patsyn/should_fail/T15695.stderr
@@ -0,0 +1,45 @@
+
+T15695.hs:39:14: warning: [-Wdeferred-type-errors (in -Wdefault)]
+ • Could not deduce: a2 ~ NA 'VO
+ from the context: ((* -> * -> *) ~ (k1 -> k2 -> *), Either ~~ f,
+ ctx ~~ (a2 ':&: (a3 ':&: 'E)), f a2 ~~ f1, f1 a3 ~~ a4)
+ bound by a pattern with pattern synonym:
+ ASSO :: forall kind (a :: kind) (b :: Ctx kind).
+ () =>
+ forall ks k (f :: k -> ks) (a1 :: k) ks1 k1 (f1 :: k1 -> ks1)
+ (a2 :: k1) a3.
+ (kind ~ (k -> k1 -> *), a ~~ f, b ~~ (a1 ':&: (a2 ':&: 'E)),
+ f a1 ~~ f1, f1 a2 ~~ a3) =>
+ a3 -> ApplyT kind a b,
+ in an equation for ‘from'’
+ at T15695.hs:39:8-21
+ ‘a2’ is a rigid type variable bound by
+ a pattern with pattern synonym:
+ ASSO :: forall kind (a :: kind) (b :: Ctx kind).
+ () =>
+ forall ks k (f :: k -> ks) (a1 :: k) ks1 k1 (f1 :: k1 -> ks1)
+ (a2 :: k1) a3.
+ (kind ~ (k -> k1 -> *), a ~~ f, b ~~ (a1 ':&: (a2 ':&: 'E)),
+ f a1 ~~ f1, f1 a2 ~~ a3) =>
+ a3 -> ApplyT kind a b,
+ in an equation for ‘from'’
+ at T15695.hs:39:8-21
+ Expected type: a4
+ Actual type: Either (NA 'VO) a3
+ • In the pattern: Left a
+ In the pattern: ASSO (Left a)
+ In an equation for ‘from'’: from' (ASSO (Left a)) = Here (a :* Nil)
+ • Relevant bindings include
+ from' :: ApplyT (* -> * -> *) Either ctx -> NS (NP NA) '[ '[ 'VO]]
+ (bound at T15695.hs:39:1)
+
+T15695.hs:40:26: warning: [-Wdeferred-type-errors (in -Wdefault)]
+ • Couldn't match type ‘a0 : as0’ with ‘'[]’
+ Expected type: NS (NP NA) '[ '[ 'VO]]
+ Actual type: NS (NP NA) ('[ 'VO] : a0 : as0)
+ • In the expression: There (Here undefined)
+ In an equation for ‘from'’:
+ from' (ASSO (Right b)) = There (Here undefined)
+ • Relevant bindings include
+ from' :: ApplyT (* -> * -> *) Either ctx -> NS (NP NA) '[ '[ 'VO]]
+ (bound at T15695.hs:39:1)
diff --git a/testsuite/tests/patsyn/should_fail/all.T b/testsuite/tests/patsyn/should_fail/all.T
index c029f20eb9..81e664445a 100644
--- a/testsuite/tests/patsyn/should_fail/all.T
+++ b/testsuite/tests/patsyn/should_fail/all.T
@@ -34,6 +34,7 @@ test('T11667', normal, compile_fail, [''])
test('T12165', normal, compile_fail, [''])
test('T12819', normal, compile_fail, [''])
test('UnliftedPSBind', normal, compile_fail, [''])
+test('T15695', normal, compile, ['']) # It has -fdefer-type-errors inside
test('T13349', normal, compile_fail, [''])
test('T13470', normal, compile_fail, [''])
test('T14112', normal, compile_fail, [''])
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