2 files changed, 38 insertions, 4 deletions
diff --git a/src/CabalHelper/Compiletime/Program/Stack.hs b/src/CabalHelper/Compiletime/Program/Stack.hs
index 33ba031..518e7f9 100644
--- a/src/CabalHelper/Compiletime/Program/Stack.hs
+++ b/src/CabalHelper/Compiletime/Program/Stack.hs
@@ -83,11 +83,35 @@ paths qe@QueryEnv{qeProjLoc=ProjLocStackYaml stack_yaml} cwd
     split l = let (key, ' ' : val) = span (not . isSpace) l in (key, val)
 
 listPackageCabalFiles :: QueryEnvI c 'Stack -> IO [CabalFile]
-listPackageCabalFiles qe@QueryEnv{qeProjLoc=ProjLocStackYaml stack_yaml} = do
+listPackageCabalFiles qe@QueryEnv{qeProjLoc=ProjLocStackYaml stack_yaml}
+  = handle ioerror $ do
   let projdir = takeDirectory stack_yaml
   out <- readStackCmd qe (Just projdir)
     [ "ide", "packages", "--cabal-files", "--stdout" ]
   return $ map CabalFile $ lines out
+  where
+    ioerror :: IOError -> IO a
+    ioerror ioe = (=<<) (fromMaybe (throwIO ioe)) $ runMaybeT $ do
+      stack_exe <- MaybeT $ findExecutable $ stackProgram $ qePrograms qe
+      stack_ver_str
+        <- liftIO $ trim <$> readStackCmd qe Nothing ["--numeric-version"]
+      stack_ver <- MaybeT $ return $ parseVerMay stack_ver_str
+      guard $ stack_ver < makeVersion [1,9,4]
+
+      let prog_cfg = ppShow $ qePrograms qe
+
+      liftIO $ hPutStrLn stderr $ printf
+        "\nerror: stack version too old!\
+        \\n\n\
+        \You have '%s' installed but cabal-helper needs at least\n\
+        \stack version 1.9.4+.\n\
+        \\n\
+        \FYI cabal-helper is using the following `stack` executable:\n\
+        \  %s\n\
+        \\n\
+        \Additional debugging info: QueryEnv qePrograms =\n\
+        \  %s\n" stack_ver_str stack_exe prog_cfg
+      mzero
 
 workdirArg :: QueryEnvI c 'Stack -> [String]
 workdirArg QueryEnv{qeDistDir=DistDirStack mworkdir} =
diff --git a/src/CabalHelper/Shared/Common.hs b/src/CabalHelper/Shared/Common.hs
index 4165ab0..2d4b037 100644
--- a/src/CabalHelper/Shared/Common.hs
+++ b/src/CabalHelper/Shared/Common.hs
@@ -104,6 +104,9 @@ parsePkgId bs =
 parseVer :: String -> Version
 parseVer vers = runReadP parseVersion vers
 
+parseVerMay :: String -> Maybe Version
+parseVerMay vers = runReadPMay parseVersion vers
+
 trim :: String -> String
 trim = dropWhileEnd isSpace
 
@@ -114,9 +117,16 @@ sameMajorVersionAs :: Version -> Version -> Bool
 sameMajorVersionAs a b = majorVer a == majorVer b
 
 runReadP :: ReadP t -> String -> t
-runReadP p i = case filter ((=="") . snd) $ readP_to_S p i of
-                 (a,""):[] -> a
-                 _ -> error $ "Error parsing: " ++ show i
+runReadP p i =
+  case runReadPMay p i of
+    Just x -> x
+    Nothing -> error $ "Error parsing version: " ++ show i
+
+runReadPMay :: ReadP t -> String -> Maybe t
+runReadPMay p i = case filter ((=="") . snd) $ readP_to_S p i of
+                 (a,""):[] -> Just a
+                 _ -> Nothing
+
 
 appCacheDir :: IO FilePath
 appCacheDir =