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authorAlec Theriault <alec.theriault@gmail.com>2018-01-05 09:59:59 -0800
committerAlexander Biehl <alexbiehl@gmail.com>2018-02-01 14:58:18 +0100
commit6ed6c110c874a746b002aca148192c3cbc819d7f (patch)
tree0bd3be02e0b402affbc474fd695db523021772ab /haddock-api/src/Haddock/Interface
parent9fd7f8bff6bdb6459fbecdc02db09789cfb6c816 (diff)
Fix infinite loop when specializing instance heads (#723)
* Fix infinite loop when specializing instance heads The bug can only be triggered from TH, hence why it went un-noticed for so long. * Add test for #679 and #710
Diffstat (limited to 'haddock-api/src/Haddock/Interface')
-rw-r--r--haddock-api/src/Haddock/Interface/Specialize.hs20
1 files changed, 10 insertions, 10 deletions
diff --git a/haddock-api/src/Haddock/Interface/Specialize.hs b/haddock-api/src/Haddock/Interface/Specialize.hs
index 6d2888d3..bb27f10c 100644
--- a/haddock-api/src/Haddock/Interface/Specialize.hs
+++ b/haddock-api/src/Haddock/Interface/Specialize.hs
@@ -31,23 +31,23 @@ import qualified Data.Set as Set
specialize :: forall name a. (Ord (IdP name), DataId name, NamedThing (IdP name))
=> Data a
=> [(IdP name, HsType name)] -> a -> a
-specialize specs = go
+specialize specs = go spec_map0
where
- go :: forall x. Data x => x -> x
- go = everywhereButType @name $ mkT $ sugar . strip_kind_sig . specialize_ty_var
+ go :: forall x. Data x => Map name (HsType name) -> x -> x
+ go spec_map = everywhereButType @name $ mkT $ sugar . strip_kind_sig . specialize_ty_var spec_map
strip_kind_sig :: HsType name -> HsType name
strip_kind_sig (HsKindSig (L _ t) _) = t
strip_kind_sig typ = typ
- specialize_ty_var :: HsType name -> HsType name
- specialize_ty_var (HsTyVar _ (L _ name'))
+ specialize_ty_var :: Map name (HsType name) -> HsType name -> HsType name
+ specialize_ty_var spec_map (HsTyVar _ (L _ name'))
| Just t <- Map.lookup name' spec_map = t
- specialize_ty_var typ = typ
- -- This is a tricky recursive definition that is guaranteed to terminate
- -- because a type binder cannot be instantiated with a type that depends
- -- on that binder. i.e. @a -> Maybe a@ is invalid
- spec_map = Map.fromList [ (n, go t) | (n, t) <- specs]
+ specialize_ty_var _ typ = typ
+
+ -- This is a tricky recursive definition. By adding in the specializations
+ -- one by one, we should avoid infinite loops.
+ spec_map0 = foldr (\(n,t) acc -> Map.insert n (go acc t) acc) mempty specs
-- | Instantiate given binders with corresponding types.