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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2022-12-20 15:52:47 +0000 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2022-12-22 23:41:07 -0500 |
| commit | 317f45c154f6fe25d50ef2f3febcc5883ff1b1ca (patch) | |
| tree | 0b9c77e0ff666dce088f29c51c309d54dbd3f381 /compiler | |
| parent | 35267f077ac226d4fbe3f14fce2dd240fb61e188 (diff) | |
| download | haskell-317f45c154f6fe25d50ef2f3febcc5883ff1b1ca.tar.gz | |
Fix unifier bug: failing to decompose over-saturated type family
This simple patch fixes #22647
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/GHC/Core/Unify.hs | 28 |
1 files changed, 15 insertions, 13 deletions
diff --git a/compiler/GHC/Core/Unify.hs b/compiler/GHC/Core/Unify.hs index e0594cb811..0ac530d8bd 100644 --- a/compiler/GHC/Core/Unify.hs +++ b/compiler/GHC/Core/Unify.hs @@ -1054,20 +1054,11 @@ unify_ty env ty1 ty2 _kco ; unless (um_inj_tf env) $ -- See (end of) Note [Specification of unification] don'tBeSoSure MARTypeFamily $ unify_tys env noninj_tys1 noninj_tys2 } - | Just (tc1, _) <- mb_tc_app1 - , not (isGenerativeTyCon tc1 Nominal) - -- E.g. unify_ty (F ty1) b = MaybeApart - -- because the (F ty1) behaves like a variable - -- NB: if unifying, we have already dealt - -- with the 'ty2 = variable' case - = maybeApart MARTypeFamily + | isTyFamApp mb_tc_app1 -- A (not-over-saturated) type-family application + = maybeApart MARTypeFamily -- behaves like a type variable; might match - | Just (tc2, _) <- mb_tc_app2 - , not (isGenerativeTyCon tc2 Nominal) - , um_unif env - -- E.g. unify_ty [a] (F ty2) = MaybeApart, when unifying (only) - -- because the (F ty2) behaves like a variable - -- NB: we have already dealt with the 'ty1 = variable' case + | isTyFamApp mb_tc_app2 -- A (not-over-saturated) type-family application + , um_unif env -- behaves like a type variable; might unify = maybeApart MARTypeFamily -- TYPE and CONSTRAINT are not Apart @@ -1169,6 +1160,17 @@ unify_tys env orig_xs orig_ys -- Possibly different saturations of a polykinded tycon -- See Note [Polykinded tycon applications] +isTyFamApp :: Maybe (TyCon, [Type]) -> Bool +-- True if we have a saturated or under-saturated type family application +-- If it is /over/ saturated then we return False. E.g. +-- unify_ty (F a b) (c d) where F has arity 1 +-- we definitely want to decompose that type application! (#22647) +isTyFamApp (Just (tc, tys)) + = not (isGenerativeTyCon tc Nominal) -- Type family-ish + && not (tys `lengthExceeds` tyConArity tc) -- Not over-saturated +isTyFamApp Nothing + = False + --------------------------------- uVar :: UMEnv -> InTyVar -- Variable to be unified |