feat: do not invalidate hash when moving type in other module

Close tweag#202

cas/hashable/src/Data/CAS/ContentHashable.hs

@@ -227,6 +227,7 @@ contentHashUpdate_fingerprint :: (Monad m, Typeable a) => Context SHA256 -> a ->
 contentHashUpdate_fingerprint ctx = contentHashUpdate ctx . stableFingerPrint
 
 -- | This only changes when the typename change
+-- TODO: understand if that's really required.
 stableFingerPrint = show . typeOf
 
 -- | Update hash context by combining 'contentHashUpdate_fingerprint' and 'contentHashUpdate_storable'.
@@ -486,11 +487,15 @@ instance (Constructor c, GContentHashable m f) => GContentHashable m (C1 c f) wh
       nameCtx = hashUpdate ctx0 $ C8.pack (conName x)
 
 instance (Datatype d, GContentHashable m f) => GContentHashable m (D1 d f) where
-  gContentHashUpdate ctx0 x = packageCtx `seq` gContentHashUpdate packageCtx (unM1 x)
+  gContentHashUpdate ctx0 x = datatypeCtx `seq` gContentHashUpdate packageCtx (unM1 x)
     where
+      -- Only add the datatype context in the hash
+      -- Adding the module and package would lead to hash invalidation when
+      -- moving the type to another module
+      -- See https://github.com/tweag/funflow/issues/202
       datatypeCtx = hashUpdate ctx0 $ C8.pack (datatypeName x)
-      moduleCtx = hashUpdate datatypeCtx $ C8.pack (datatypeName x)
-      packageCtx = hashUpdate moduleCtx $ C8.pack (datatypeName x)
+      -- moduleCtx = hashUpdate datatypeCtx $ C8.pack (datatypeName x)
+      -- packageCtx = hashUpdate moduleCtx $ C8.pack (datatypeName x)
 
 instance GContentHashable m f => GContentHashable m (S1 s f) where
   gContentHashUpdate ctx x = gContentHashUpdate ctx (unM1 x)