Make cabal sdist fail with an informative error message`

Setup.hs

@@ -28,7 +28,7 @@ main = defaultMainWithHooks simpleUserHooks{ preBuild  = gfPreBuild
                                            , postInst  = gfPostInst
                                            , preCopy   = const . checkRGLArgs
                                            , postCopy  = gfPostCopy
---                                         , sDistHook = sdistRGL
+                                           , sDistHook = sdistError
                                            }
   where
     gfPreBuild args  = gfPre args . buildDistPref
@@ -182,6 +182,12 @@ sdistRGL pkg mb_lbi hooks flags = do
                else return paths
         else getRGLFiles path paths
 -}
+
+-- | Cabal doesn't know how to correctly create the source distribution, so
+-- we print an error message with the correct instructions when someone tries
+-- `cabal sdist`.
+sdistError _ _ _ _ = fail "Error: Use `make sdist` to create the source distribution file"
+
 rgl_src_dir         = "lib" </> "src"
 rgl_dst_dir lbi = buildDir lbi </> "rgl"