Merge pull request #263 from gdevanla/master

add TopLevel placeHolder to builtins module

src/Nix/Builtins.hs

@@ -167,6 +167,7 @@ builtinsList = sequence [
     , add  Normal   "parseDrvName"               parseDrvName
     , add2 Normal   "partition"                  partition_
     , add  Normal   "pathExists"                 pathExists_
+    , add  TopLevel "placeholder"                placeHolder
     , add  Normal   "readDir"                    readDir_
     , add  Normal   "readFile"                   readFile_
     , add2 TopLevel "removeAttrs"                removeAttrs
@@ -766,6 +767,11 @@ hashString algo s = Prim $ do
             ++ "expected \"md5\", \"sha1\", \"sha256\", or \"sha512\", got " ++ show algo
     pure $ decodeUtf8 $ Base16.encode $ hash $ encodeUtf8 s
 
+placeHolder :: MonadNix e m => m (NValue m) -> m (NValue m)
+placeHolder = fromValue @Text >=> \_ -> hash $ Text.pack "fdasdfas"
+  where
+    hash x = (toBuiltin "") . hashString (Text.pack "sha256") $ x
+
 absolutePathFromValue :: MonadNix e m => NValue m -> m FilePath
 absolutePathFromValue = \case
     NVStr pathText _ -> do

tests/EvalTests.hs

@@ -144,6 +144,9 @@ let
 in [ (fix toFixFold) (fix toFix) ]
 |]
 
+case_placeholder =
+  constantEqualText "\"ed0d01fb5aba979d0beeffb3c2bdffb5cfda021955b776cce0a47058708b3157\"" "builtins.placeholder \"out\""
+
 -----------------------
 
 tests :: TestTree