feat: add --file flag (#64)

src/NixTree/Main.hs

@@ -20,6 +20,7 @@ version = VERSION_nix_tree
 data Opts = Opts
   { oInstallables :: [Installable],
     oStore :: Maybe String,
+    oFile :: Maybe FilePath,
     oVersion :: Bool,
     oDerivation :: Bool,
     oImpure :: Bool,
@@ -64,6 +65,15 @@ optsParser =
                     )
               )
           )
+        <*> optional
+          ( Opts.strOption
+              ( Opts.long "file"
+                  <> Opts.metavar "FILE"
+                  <> Opts.helpDoc
+                    ( Just $ Opts.vsep ["Interpret installables as attribute paths relative to the Nix expression stored in file."]
+                    )
+              )
+          )
         <*> Opts.switch (Opts.long "version" <> Opts.help "Show the nix-tree version")
         <*> Opts.switch (Opts.long "derivation" <> Opts.help "Operate on the store derivation rather than its outputs")
         <*> Opts.switch (Opts.long "impure" <> Opts.help "Allow access to mutable paths and repositories")
@@ -113,7 +123,8 @@ main = do
         StoreEnvOptions
           { seoIsDerivation = opts & oDerivation,
             seoIsImpure = opts & oImpure,
-            seoStoreURL = opts & oStore
+            seoStoreURL = opts & oStore,
+            seoFile = opts & oFile
           }
 
   withStoreEnv seo installables $ \env' -> do

src/NixTree/StorePath.hs

@@ -154,7 +154,8 @@ data PathInfoOptions = PathInfoOptions
   { pioIsRecursive :: Bool,
     pioIsDerivation :: Bool,
     pioIsImpure :: Bool,
-    pioStoreURL :: Maybe FilePath
+    pioStoreURL :: Maybe FilePath,
+    pioFile :: Maybe FilePath
   }
 
 getPathInfo :: NixStore -> NixVersion -> PathInfoOptions -> NonEmpty Installable -> IO (NonEmpty (StorePath s (StoreName s) ()))
@@ -172,6 +173,10 @@ getPathInfo nixStore nixVersion options names = do
                        Nothing -> []
                        Just url -> ["--store", url]
                    )
+                ++ ( case options & pioFile of
+                       Nothing -> []
+                       Just file -> ["--file", file]
+                   )
                 ++ (if nixVersion >= Nix2_4 then ["--extra-experimental-features", "nix-command flakes"] else [])
                 ++ map (toString . installableToText) (toList names)
             )
@@ -213,7 +218,8 @@ data StoreEnv s payload = StoreEnv
 data StoreEnvOptions = StoreEnvOptions
   { seoIsDerivation :: Bool,
     seoIsImpure :: Bool,
-    seoStoreURL :: Maybe String
+    seoStoreURL :: Maybe String,
+    seoFile :: Maybe String
   }
 
 withStoreEnv ::
@@ -223,7 +229,7 @@ withStoreEnv ::
   NonEmpty Installable ->
   (forall s. StoreEnv s () -> m a) ->
   m a
-withStoreEnv StoreEnvOptions {seoIsDerivation, seoIsImpure, seoStoreURL} names cb = do
+withStoreEnv StoreEnvOptions {seoIsDerivation, seoIsImpure, seoStoreURL, seoFile} names cb = do
   nixStore <- liftIO $ getStoreDir seoStoreURL
 
   -- See: https://github.com/utdemir/nix-tree/issues/12
@@ -238,15 +244,15 @@ withStoreEnv StoreEnvOptions {seoIsDerivation, seoIsImpure, seoStoreURL} names c
       getPathInfo
         nixStore
         nixVersion
-        (PathInfoOptions {pioIsDerivation = seoIsDerivation, pioIsRecursive = False, pioIsImpure = seoIsImpure, pioStoreURL = seoStoreURL})
+        (PathInfoOptions {pioIsDerivation = seoIsDerivation, pioIsRecursive = False, pioIsImpure = seoIsImpure, pioStoreURL = seoStoreURL, pioFile = seoFile})
         names
 
   paths <-
     liftIO $
       getPathInfo
         nixStore
         nixVersion
-        (PathInfoOptions {pioIsDerivation = seoIsDerivation, pioIsRecursive = True, pioIsImpure = seoIsImpure, pioStoreURL = seoStoreURL})
+        (PathInfoOptions {pioIsDerivation = seoIsDerivation, pioIsRecursive = True, pioIsImpure = seoIsImpure, pioStoreURL = seoStoreURL, pioFile = seoFile})
         (Installable . toText . storeNameToPath . spName <$> roots)
 
   let env =