Merge: Remove exitSuccess from diffEbuilds

The diffEbuilds function calls exitSuccess which terminates the program
and prevents any more output from being displayed. This seems like a
mistake, and in any event it prevents warnings from being displayed at
the end of the output.

Signed-off-by: hololeap <[email protected]>

src/Merge.hs

@@ -55,7 +55,7 @@ import           System.Directory ( getCurrentDirectory
                         )
 import           System.Process
 import           System.FilePath ((</>),(<.>))
-import           System.Exit (ExitCode(ExitSuccess), exitSuccess)
+import           System.Exit (ExitCode(ExitSuccess))
 
 -- hackport
 import qualified AnsiColor as A
@@ -89,11 +89,10 @@ Requested features:
 -}
 
 -- | Call @diff@ between two ebuilds.
-diffEbuilds :: FilePath -> Portage.PackageId -> Portage.PackageId -> IO ()
-diffEbuilds fp a b = do _ <- system $ "diff -u --color=auto "
-                             ++ fp </> Portage.packageIdToFilePath a ++ " "
-                             ++ fp </> Portage.packageIdToFilePath b
-                        exitSuccess
+diffEbuilds :: FilePath -> Portage.PackageId -> Portage.PackageId -> IO ExitCode
+diffEbuilds fp a b = system $ "diff -u --color=auto "
+    ++ fp </> Portage.packageIdToFilePath a ++ " "
+    ++ fp </> Portage.packageIdToFilePath b
 
 -- | Given a list of available packages, and maybe a preferred version,
 -- return the available package with that version. Latest version is chosen
@@ -196,8 +195,11 @@ merge repoContext packageString users_cabal_flags
       newPkgId = Portage.fromCabalPackageId cat cabal_pkgId
   pkgDir <- liftIO $ listDirectory pkgPath
   case Merge.getPreviousPackageId pkgDir newPkgId of
-    Just validPkg -> do info "Generating a diff..."
-                        liftIO $ diffEbuilds overlayPath validPkg newPkgId
+    Just validPkg -> do
+      info "Generating a diff..."
+      -- Ignore the ExitCode generated by diff
+      _ <- liftIO $ diffEbuilds overlayPath validPkg newPkgId
+      pure ()
     _ -> info "Nothing to diff!"
 
 -- used to be FlagAssignment in Cabal but now it's an opaque type