Output lint errors on stderr, small comment about more lint opportuni…

…ties

Development/Shake/Core.hs

@@ -72,6 +72,7 @@ import Data.Time.Clock (UTCTime, NominalDiffTime, getCurrentTime, diffUTCTime)
 import Data.Foldable (traverse_)
 
 import System.Environment
+import System.IO
 import System.IO.Unsafe (unsafePerformIO) -- For command line parsing hack only
 
 import GHC.Conc (numCapabilities)
@@ -858,5 +859,5 @@ runActLinted creates_fps e action = do
     -- User code transitioned from ss to ss' before returning without needing anything else
     mb_sss <- retakeSnapshot []
     -- FIXME: accumulate errors rather than showing them eagerly like this
-    liftIO $ mapM_ putStrLn $ lintSnapshots creates_fps (reverse $ maybe id (:) mb_sss (as_snapshots final_nested_s))
+    liftIO $ mapM_ (hPutStrLn stderr) $ lintSnapshots creates_fps (reverse $ maybe id (:) mb_sss (as_snapshots final_nested_s))
     return (as_this_history final_nested_s, res)

Development/Shake/Files.hs

@@ -136,6 +136,7 @@ instance Namespace CanonicalFilePath where
              then return (seen', S.insert fp seen_files)
              else getDirectoryContents (canonicalFilePath fp) >>= (foldM (explore fp) (seen', seen_files) . map (originalFilePath fp </>))
 
+    -- TODO: I could lint modification times as well? For example, you should probably not modify a file you need
     lintSnapshots building_fps = go S.empty S.empty S.empty
       where
         go needed accessed accessed_without_need history = case history of