[Git][ghc/ghc][wip/jeltsch/smaller-pit] Make `IfaceBinHandle` a type synonym family

12 Oct 2026


      Wolfgang Jeltsch pushed to branch wip/jeltsch/smaller-pit at Glasgow Haskell Compiler / GHC


Commits:
969e7ea7 by Wolfgang Jeltsch at 2026-10-12T17:42:15+03:00
Make `IfaceBinHandle` a type synonym family

This brings the handling of `IfaceBinHandle` somewhat in line with how
other phase-dependent data is handled. Note that `mi_hi_bytes_` now
includes the `Strict.Maybe` layer itself, independently of the phase.
This is necessary, because with a type family instead of a GADT
`clear_mi_hi_bytes` cannot determine the phase at runtime anymore and
thus has to set `mi_hi_bytes_` to `Strict.Nothing` for every phase.

- - - - -


3 changed files:

- compiler/GHC/Iface/Binary.hs
- compiler/GHC/Iface/Make.hs
- compiler/GHC/Unit/Module/ModIface.hs


Changes:

=====================================
compiler/GHC/Iface/Binary.hs
=====================================
@@ -197,7 +197,7 @@ getIfaceWithExtFields name_cache bh = do
   modIfaceBinData <- freezeBinHandle bh start
   pure $ mod_iface
     & set_mi_ext_fields extFields
-    & set_mi_hi_bytes (FullIfaceBinHandle $ Strict.Just modIfaceBinData)
+    & set_mi_hi_bytes (Strict.Just modIfaceBinData)
 
 -- | This performs a get action after reading the dictionary and symbol
 -- table. It is necessary to run this before trying to deserialise any
@@ -276,10 +276,10 @@ writeBinIface profile traceBinIface compressionLevel hi_path mod_iface = do
 putIfaceWithExtFields :: TraceBinIFace -> CompressionIFace -> WriteBinHandle -> ModIface -> IO ()
 putIfaceWithExtFields traceBinIface compressionLevel bh mod_iface =
   case mi_hi_bytes mod_iface of
-    FullIfaceBinHandle Strict.Nothing -> do
+    Strict.Nothing -> do
       forwardPutRel_ bh (\_ -> put_ bh (mi_ext_fields mod_iface)) $ do
         putWithUserData traceBinIface compressionLevel bh mod_iface
-    FullIfaceBinHandle (Strict.Just binData) -> putFullBinData bh binData
+    Strict.Just binData -> putFullBinData bh binData
 
 -- | Put a piece of data with an initialised `UserData` field. This
 -- is necessary if you want to serialise Names or FastStrings.


=====================================
compiler/GHC/Iface/Make.hs
=====================================
@@ -77,6 +77,7 @@ import GHC.Iface.Binary
 
 import GHC.Data.FastString
 import GHC.Data.Maybe
+import qualified GHC.Data.Strict as Strict
 
 import GHC.HsToCore.Docs
 import GHC.HsToCore.Usage
@@ -394,7 +395,7 @@ mkIface_ hsc_env
           & set_mi_docs             docs
           & set_mi_abi_hashes       ()
           & set_mi_ext_fields       emptyExtensibleFields
-          & set_mi_hi_bytes         PartialIfaceBinHandle
+          & set_mi_hi_bytes         Strict.Nothing
 
   where
      cmp_rule     = lexicalCompareFS `on` ifRuleName


=====================================
compiler/GHC/Unit/Module/ModIface.hs
=====================================
@@ -70,7 +70,7 @@ module GHC.Unit.Module.ModIface
    , set_mi_hash_fn
    , completePartialModIface
    , shrinkModIface
-   , IfaceBinHandle(..)
+   , IfaceBinHandle
    , PartialModIface
    , RetainedModIface
    , IfaceAbiHashes (..)
@@ -160,6 +160,7 @@ import GHC.Utils.Binary
 
 import Control.DeepSeq
 import Control.Exception
+import Data.Void (Void)
 
 
 {- Note [Interface file stages]
@@ -236,15 +237,10 @@ data ModIfacePhase
 -- | In-memory byte array representation of a 'ModIface'.
 --
 -- See Note [Sharing of ModIface] for why we need this.
-data IfaceBinHandle (phase :: ModIfacePhase) where
-  -- | A partial 'ModIface' cannot be serialised to disk.
-  PartialIfaceBinHandle :: IfaceBinHandle 'ModIfaceCore
-  -- | Optional 'FullBinData' that can be serialised to disk directly.
-  --
-  -- See Note [Private fields in ModIface] for when this fields needs to be cleared
-  -- (e.g., set to 'Nothing').
-  FullIfaceBinHandle :: !(Strict.Maybe FullBinData) -> IfaceBinHandle 'ModIfaceFinal
-  RetainedIfaceBinHandle :: IfaceBinHandle 'ModIfaceRetained
+type family IfaceBinHandle (phase :: ModIfacePhase) where
+  IfaceBinHandle 'ModIfaceCore     = Void
+  IfaceBinHandle 'ModIfaceFinal    = FullBinData
+  IfaceBinHandle 'ModIfaceRetained = Void
 
 type family IfaceSelfRecompData (phase :: ModIfacePhase) where
   IfaceSelfRecompData 'ModIfaceCore     = Maybe IfaceSelfRecomp
@@ -322,11 +318,22 @@ withSelfRecomp iface nk jk =
 -- fields.
 data ModIface_ (phase :: ModIfacePhase)
   = PrivateModIface {
-        mi_hi_bytes_ :: !(IfaceBinHandle phase),
-                -- ^ A serialised in-memory buffer of this 'ModIface'.
-                -- If this handle is given, we can avoid serialising the 'ModIface'
-                -- when writing this 'ModIface' to disk, and write this buffer to disk instead.
-                -- See Note [Sharing of ModIface].
+        mi_hi_bytes_ :: !(Strict.Maybe (IfaceBinHandle phase)),
+                -- ^ Optionally an in-memory buffer that contains the
+                --   serialization of this 'ModIface'. If such a buffer is
+                --   present, we can avoid serialising the 'ModIface' when
+                --   writing it to disk and write this buffer instead. See
+                --   Note [Sharing of ModIface] and
+                --   Note [Private fields in ModIface].
+                --
+                --   Only in the 'ModIfaceFinal' phase, there can be a buffer
+                --   with the serialization. Both @IfaceBinHandle 'ModIfaceCore@
+                --   and @IfaceBinHandle 'ModIfaceRetained@ are defined to be
+                --   'Void', so that the 'mi_hi_bytes' field gets the type
+                --   @Strict.Maybe Void@. This type is isomorphic to '()', even
+                --   when taking partially defined values into account, because
+                --   @Strict.Just undefined@ is @undefined@ and so @Nothing@ and
+                --   @undefined@ are the only inhabitants of that type.
         mi_iface_hash_  :: Fingerprint, -- A hash of the whole interface
 
         mi_mod_info_     :: IfaceModInfo,
@@ -718,7 +725,7 @@ instance Binary ModIface where
                  -- We can't populate this field here, as we are
                  -- missing the 'mi_ext_fields_' field, which is
                  -- handled in 'getIfaceWithExtFields'.
-                 mi_hi_bytes_    = FullIfaceBinHandle Strict.Nothing
+                 mi_hi_bytes_    = Strict.Nothing
                  })
 
 instance Binary IfaceModInfo where
@@ -833,7 +840,7 @@ emptyPartialModIface mod
   = PrivateModIface
       { mi_mod_info_    = emptyIfaceModInfo mod,
         mi_iface_hash_  = fingerprint0,
-        mi_hi_bytes_    = PartialIfaceBinHandle,
+        mi_hi_bytes_    = Strict.Nothing,
         mi_deps_        = noDependencies,
         mi_public_      = emptyPublicModIface [] [] [] [] [] [] [] (),
         mi_simplified_core_ = Nothing,
@@ -907,7 +914,7 @@ emptyFullModIface :: Module -> ModIface
 emptyFullModIface mod =
     (emptyPartialModIface mod)
       { mi_public_ = emptyPublicModIface [] [] [] [] [] [] [] emptyIfaceBackend
-      , mi_hi_bytes_ = FullIfaceBinHandle Strict.Nothing
+      , mi_hi_bytes_ = Strict.Nothing
       }
 
 
@@ -940,7 +947,7 @@ instance ( NFData (IfaceSelfRecompData phase)
          , NFData (IfaceAbiHashesData phase)
          ) => NFData (ModIface_ phase) where
   rnf (PrivateModIface a1 a2 a3 a4 a5 a6 a7 a8 a9 a10)
-    = (a1 :: IfaceBinHandle phase)
+    = a1
     `seq` rnf a2
     `seq` rnf a3
     `seq` rnf a4
@@ -1051,7 +1058,7 @@ completePartialModIface :: PartialModIface
 completePartialModIface partial iface_hash decls extra_decls final_exts cache = partial
   { mi_public_ = completePublicModIface decls final_exts cache (mi_public_ partial)
   , mi_simplified_core_ = extra_decls
-  , mi_hi_bytes_ = FullIfaceBinHandle Strict.Nothing
+  , mi_hi_bytes_ = Strict.Nothing
   , mi_iface_hash_ = iface_hash
   }
 
@@ -1072,7 +1079,7 @@ shrinkModIface :: ModIface -> RetainedModIface
 shrinkModIface PrivateModIface {..}
   = PrivateModIface
     {
-      mi_hi_bytes_        = RetainedIfaceBinHandle,
+      mi_hi_bytes_        = Strict.Nothing,
       mi_public_          = shrinkIfacePublic mi_public_,
       mi_self_recomp_     = (),
       mi_simplified_core_ = (),
@@ -1100,7 +1107,7 @@ set_mi_mod_info val iface = clear_mi_hi_bytes $ iface { mi_mod_info_ = val }
 set_mi_self_recomp :: IfaceSelfRecompData phase -> ModIface_ phase -> ModIface_ phase
 set_mi_self_recomp val iface = clear_mi_hi_bytes $ iface { mi_self_recomp_ = val }
 
-set_mi_hi_bytes :: IfaceBinHandle phase -> ModIface_ phase -> ModIface_ phase
+set_mi_hi_bytes :: Strict.Maybe (IfaceBinHandle phase) -> ModIface_ phase -> ModIface_ phase
 set_mi_hi_bytes val iface = iface { mi_hi_bytes_ = val }
 
 set_mi_deps :: Dependencies -> ModIface_ phase -> ModIface_ phase
@@ -1203,12 +1210,7 @@ set_mi_mod_info_field f iface = clear_mi_hi_bytes $ iface { mi_mod_info_ = f (mi
 
 -- | Invalidate any byte array buffer we might have.
 clear_mi_hi_bytes :: ModIface_ phase -> ModIface_ phase
-clear_mi_hi_bytes iface = iface
-  { mi_hi_bytes_ = case mi_hi_bytes iface of
-      PartialIfaceBinHandle  -> PartialIfaceBinHandle
-      FullIfaceBinHandle _   -> FullIfaceBinHandle Strict.Nothing
-      RetainedIfaceBinHandle -> RetainedIfaceBinHandle
-  }
+clear_mi_hi_bytes iface = iface { mi_hi_bytes_ = Strict.Nothing }
 
 -- ----------------------------------------------------------------------------
 -- 'ModIface' pattern synonyms to keep breakage low.
@@ -1319,7 +1321,7 @@ pattern ModIface ::
   -> Maybe Docs
   -> IfaceAbiHashesData phase
   -> ExtensibleFieldsData phase
-  -> IfaceBinHandle phase
+  -> Strict.Maybe (IfaceBinHandle phase)
   -> IfaceSelfRecompData phase
   -> (OccName -> Maybe Fixity)
   -> (OccName -> Maybe (OccName, Fingerprint))



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/969e7ea7de61ae6ad2976042e4449ef3...

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/969e7ea7de61ae6ad2976042e4449ef3...
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Wolfgang Jeltsch (＠jeltsch)

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