updates Bindist functions as per https://gitlab.haskell.org/haskell/ghcup-hs/-/merge_requests/127#note_366702

lib/GHCup.hs

@@ -204,14 +204,13 @@ installGHCBindist :: ( MonadFail m
                        ()
 installGHCBindist dlinfo ver isoFilepath = do
   let tver = mkTVer ver
-  let isIsolatedInstall = isJust isoFilepath
-
 
   lift $ $(logDebug) [i|Requested to install GHC with #{ver}|]
 
+  case isoFilepath of
     -- we only care for already installed errors in regular (non-isolated) installs
-  when (not isIsolatedInstall) $
-    whenM (lift $ ghcInstalled tver) (throwE $ AlreadyInstalled GHC ver)
+    Nothing -> whenM (lift $ ghcInstalled tver) (throwE $ AlreadyInstalled GHC ver)
+    _ -> pure ()
 
   -- download (or use cached version)
   dl <- liftE $ downloadCached dlinfo Nothing
@@ -219,21 +218,16 @@ installGHCBindist dlinfo ver isoFilepath = do
   -- prepare paths
   ghcdir <- lift $ ghcupGHCDir tver
 
-  let isoDir = if isIsolatedInstall
-               then fromJust isoFilepath
-               else mempty :: FilePath
-
-  if isIsolatedInstall
-  then do
+  case isoFilepath of
+    Just isoDir -> do                        -- isolated install
       lift $ $(logInfo) [i|isolated installing GHC to #{isoDir}|]
       liftE $ installPackedGHC dl (view dlSubdir dlinfo) isoDir ver
-  else do
+    Nothing -> do                            -- regular install
       toolchainSanityChecks
       liftE $ installPackedGHC dl (view dlSubdir dlinfo) ghcdir ver
 
       -- make symlinks & stuff when regular install,
-  -- don't make any for isolated installs.
-  whenM (pure $ not isIsolatedInstall) (liftE $ postGHCInstall tver)
+      liftE $ postGHCInstall tver
 
  where
   toolchainSanityChecks = do
@@ -419,10 +413,8 @@ installCabalBindist dlinfo ver isoFilepath = do
   PlatformRequest {..} <- lift getPlatformReq
   Dirs {..} <- lift getDirs
 
-  let isIsolatedInstall = isJust isoFilepath
-
-  -- check if cabal already installed in regular (non-isolated) installs
-  when (not isIsolatedInstall) $
+  case isoFilepath of
+    Nothing -> -- for regular install check if any previous versions installed
       whenM
         (lift (cabalInstalled ver) >>= \a -> liftIO $
           handleIO (\_ -> pure False)
@@ -432,6 +424,8 @@ installCabalBindist dlinfo ver isoFilepath = do
         )
         (throwE $ AlreadyInstalled Cabal ver)
 
+    _ -> pure () -- check isn't required in isolated installs
+
   -- download (or use cached version)
   dl <- liftE $ downloadCached dlinfo Nothing
 
@@ -443,18 +437,15 @@ installCabalBindist dlinfo ver isoFilepath = do
   -- the subdir of the archive where we do the work
   workdir <- maybe (pure tmpUnpack) (liftE . intoSubdir tmpUnpack) (view dlSubdir dlinfo)
 
-  let isoDir = fromJust isoFilepath
-
-  if isIsolatedInstall
-  then do
+  case isoFilepath of
+    Just isoDir -> do             -- isolated install
       lift $ $(logInfo) [i|isolated installing Cabal to #{isoDir}|]
       liftE $ installCabalUnpacked workdir isoDir ver
-  else do
+
+    Nothing -> do                 -- regular install
       liftE $ installCabalUnpacked workdir binDir ver
 
-  -- create symlink if this is the latest version
-  -- not applicable for isolated installs  
-  whenM (pure $ not isIsolatedInstall) $ do
+      -- create symlink if this is the latest version for regular installs
       cVers <- lift $ fmap rights getInstalledCabals
       let lInstCabal = headMay . reverse . sort $ cVers
       when (maybe True (ver >=) lInstCabal) $ liftE $ setCabal ver
@@ -552,13 +543,14 @@ installHLSBindist dlinfo ver isoFilepath = do
   PlatformRequest {..} <- lift getPlatformReq
   Dirs {..} <- lift getDirs
 
-  let isIsolatedInstall = isJust isoFilepath
-
+  case isoFilepath of
+    Nothing ->
       -- we only check for already installed in regular (non-isolated) installs
-  when (not isIsolatedInstall) $
       whenM (lift (hlsInstalled ver))
       (throwE $ AlreadyInstalled HLS ver)
 
+    _ -> pure ()
+
   -- download (or use cached version)
   dl <- liftE $ downloadCached dlinfo Nothing
 
@@ -569,21 +561,21 @@ installHLSBindist dlinfo ver isoFilepath = do
 
   -- the subdir of the archive where we do the work
   workdir <- maybe (pure tmpUnpack) (liftE . intoSubdir tmpUnpack) (view dlSubdir dlinfo)
-  let isoDir = fromJust isoFilepath
 
-  if isIsolatedInstall
-  then do
+  case isoFilepath of
+    Just isoDir -> do
       lift $ $(logInfo) [i|isolated installing HLS to #{isoDir}|]
       liftE $ installHLSUnpacked workdir isoDir ver
-  else do
+
+    Nothing -> do
       liftE $ installHLSUnpacked workdir binDir ver
 
       -- create symlink if this is the latest version in a regular install
-  whenM (pure $ not isIsolatedInstall) $ do
       hlsVers <- lift $ fmap rights getInstalledHLSs
       let lInstHLS = headMay . reverse . sort $ hlsVers
       when (maybe True (ver >=) lInstHLS) $ liftE $ setHLS ver
 
+
 -- | Install an unpacked hls distribution.
 installHLSUnpacked :: (MonadFail m, MonadLogger m, MonadCatch m, MonadIO m)
               => FilePath      -- ^ Path to the unpacked hls bindist (where the executable resides)
@@ -730,12 +722,13 @@ installStackBindist dlinfo ver isoFilepath = do
   PlatformRequest {..} <- lift getPlatformReq
   Dirs {..} <- lift getDirs
 
-  let isIsolatedInstall = isJust isoFilepath
-
-  when (not isIsolatedInstall) $ 
+  case isoFilepath of
+    Nothing ->             -- check previous versions in case of regular installs
       whenM (lift (stackInstalled ver))
       (throwE $ AlreadyInstalled Stack ver)
 
+    _ -> pure ()           -- don't do shit for isolates
+
   -- download (or use cached version)
   dl <- liftE $ downloadCached dlinfo Nothing
 
@@ -747,17 +740,14 @@ installStackBindist dlinfo ver isoFilepath = do
   -- the subdir of the archive where we do the work
   workdir <- maybe (pure tmpUnpack) (liftE . intoSubdir tmpUnpack) (view dlSubdir dlinfo)
 
-  let isoDir = fromJust isoFilepath
-
-  if isIsolatedInstall
-  then do
+  case isoFilepath of
+    Just isoDir -> do                 -- isolated install
       lift $ $(logInfo) [i|isolated installing Stack to #{isoDir}|]
       liftE $ installStackUnpacked workdir isoDir ver
-  else do
+    Nothing -> do                     -- regular install
       liftE $ installStackUnpacked workdir binDir ver
 
       -- create symlink if this is the latest version and a regular install
-  whenM (pure $ not isIsolatedInstall) $ do
       sVers <- lift $ fmap rights getInstalledStacks
       let lInstStack = headMay . reverse . sort $ sVers
       when (maybe True (ver >=) lInstStack) $ liftE $ setStack ver