add a readonly computeStorePathForPath

hnix-store-core/src/System/Nix/ReadonlyStore.hs

@@ -12,7 +12,9 @@ import qualified Data.Text                     as T
 import qualified Data.HashSet                  as HS
 import           Data.Text.Encoding
 import           System.Nix.Hash
+import           System.Nix.Nar
 import           System.Nix.StorePath
+import           Control.Monad.State.Strict
 
 
 makeStorePath
@@ -45,9 +47,7 @@ makeTextPath fp nm h refs = makeStorePath fp ty h nm
 
 makeFixedOutputPath
   :: forall hashAlgo
-  . ( ValidAlgo hashAlgo
-    , NamedAlgo hashAlgo
-    )
+  . (NamedAlgo hashAlgo)
   => FilePath
   -> Bool
   -> Digest hashAlgo
@@ -69,3 +69,22 @@ makeFixedOutputPath fp recursive h =
 computeStorePathForText
   :: FilePath -> StorePathName -> ByteString -> (StorePathSet -> StorePath)
 computeStorePathForText fp nm = makeTextPath fp nm . hash
+
+computeStorePathForPath
+  :: StorePathName        -- ^ Name part of the newly created `StorePath`
+  -> FilePath             -- ^ Local `FilePath` to add
+  -> Bool                 -- ^ Add target directory recursively
+  -> (FilePath -> Bool)   -- ^ Path filter function
+  -> Bool                 -- ^ Only used by local store backend
+  -> IO StorePath
+computeStorePathForPath name pth recursive _pathFilter _repair = do
+  selectedHash <- if recursive then recursiveContentHash else flatContentHash
+  pure $ makeFixedOutputPath "/nix/store" recursive selectedHash name
+ where
+  recursiveContentHash :: IO (Digest 'SHA256)
+  recursiveContentHash = finalize <$> execStateT streamNarUpdate (initialize @'SHA256)
+  streamNarUpdate :: StateT (AlgoCtx 'SHA256) IO ()
+  streamNarUpdate = streamNarIO (modify . flip (update @'SHA256)) narEffectsIO pth
+
+  flatContentHash :: IO (Digest 'SHA256)
+  flatContentHash = hashLazy <$> narReadFile narEffectsIO pth