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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2022-11-02 18:06:35 +0000 |
|---|---|---|
| committer | Simon Peyton Jones <simon.peytonjones@gmail.com> | 2022-11-25 22:31:27 +0000 |
| commit | d10dc6bdade0fdae879e5869038ce8378c2ce84f (patch) | |
| tree | e386af2c82a9e64b7c72275c2b7e9af36bea7f11 /compiler/GHC/Core | |
| parent | 13d627bbd0bc3dd30d672de341aa7f471be0aa2c (diff) | |
| download | haskell-wip/T22331.tar.gz | |
Fix decomposition of TyConAppswip/T22331
Ticket #22331 showed that we were being too eager to decompose
a Wanted TyConApp, leading to incompleteness in the solver.
To understand all this I ended up doing a substantial rewrite
of the old Note [Decomposing equalities], now reborn as
Note [Decomposing TyConApp equalities]. Plus rewrites of other
related Notes.
The actual fix is very minor and actually simplifies the code: in
`can_decompose` in `GHC.Tc.Solver.Canonical.canTyConApp`, we now call
`noMatchableIrreds`. A closely related refactor: we stop trying to
use the same "no matchable givens" function here as in
`matchClassInst`. Instead split into two much simpler functions.
Diffstat (limited to 'compiler/GHC/Core')
| -rw-r--r-- | compiler/GHC/Core/TyCon.hs | 17 |
1 files changed, 9 insertions, 8 deletions
diff --git a/compiler/GHC/Core/TyCon.hs b/compiler/GHC/Core/TyCon.hs index 2a26363c7b..0cbb9ece43 100644 --- a/compiler/GHC/Core/TyCon.hs +++ b/compiler/GHC/Core/TyCon.hs @@ -2118,12 +2118,13 @@ isTypeDataTyCon (AlgTyCon {algTcRhs = DataTyCon {is_type_data = type_data }}) isTypeDataTyCon _ = False -- | 'isInjectiveTyCon' is true of 'TyCon's for which this property holds --- (where X is the role passed in): --- If (T a1 b1 c1) ~X (T a2 b2 c2), then (a1 ~X1 a2), (b1 ~X2 b2), and (c1 ~X3 c2) --- (where X1, X2, and X3, are the roles given by tyConRolesX tc X) --- See also Note [Decomposing equality] in "GHC.Tc.Solver.Canonical" +-- (where r is the role passed in): +-- If (T a1 b1 c1) ~r (T a2 b2 c2), then (a1 ~r1 a2), (b1 ~r2 b2), and (c1 ~r3 c2) +-- (where r1, r2, and r3, are the roles given by tyConRolesX tc r) +-- See also Note [Decomposing TyConApp equalities] in "GHC.Tc.Solver.Canonical" isInjectiveTyCon :: TyCon -> Role -> Bool -isInjectiveTyCon _ Phantom = False +isInjectiveTyCon _ Phantom = True -- Vacuously; (t1 ~P t2) holes for all t1, t2! + isInjectiveTyCon (AlgTyCon {}) Nominal = True isInjectiveTyCon (AlgTyCon {algTcRhs = rhs}) Representational = isGenInjAlgRhs rhs @@ -2139,9 +2140,9 @@ isInjectiveTyCon (TcTyCon {}) _ = True -- See Note [How TcTyCons work] item (1) in GHC.Tc.TyCl -- | 'isGenerativeTyCon' is true of 'TyCon's for which this property holds --- (where X is the role passed in): --- If (T tys ~X t), then (t's head ~X T). --- See also Note [Decomposing equality] in "GHC.Tc.Solver.Canonical" +-- (where r is the role passed in): +-- If (T tys ~r t), then (t's head ~r T). +-- See also Note [Decomposing TyConApp equalities] in "GHC.Tc.Solver.Canonical" isGenerativeTyCon :: TyCon -> Role -> Bool isGenerativeTyCon (FamilyTyCon { famTcFlav = DataFamilyTyCon _ }) Nominal = True isGenerativeTyCon (FamilyTyCon {}) _ = False |