Allow to use Hadrian as build system, fixes #35

app/ghcup/Main.hs

@@ -183,6 +183,7 @@ data GHCCompileOptions = GHCCompileOptions
   , setCompile   :: Bool
   , ovewrwiteVer :: Maybe Version
   , buildFlavour :: Maybe String
+  , hadrian      :: Bool
   }
 
 data UpgradeOpts = UpgradeInplace
@@ -995,6 +996,9 @@ ghcCompileOpts =
               "Set the compile build flavour (this value depends on the build system type: 'make' vs 'hadrian')"
             )
           )
+    <*> switch
+          (long "hadrian" <> help "Use the hadrian build system instead of make (only git versions seem to be properly supported atm)"
+          )
 
 
 toolVersionParser :: Parser ToolVersion
@@ -1914,6 +1918,9 @@ Report bugs at <https://gitlab.haskell.org/haskell/ghcup-hs/issues>|]
                         runLogger $ $(logError) $ T.pack $ prettyShow e
                         pure $ ExitFailure 8
 
+            Compile (CompileGHC GHCCompileOptions { hadrian = True, crossTarget = Just _ }) -> do
+              runLogger $ $(logError) "Hadrian cross compile support is not yet implemented!"
+              pure $ ExitFailure 9
             Compile (CompileGHC GHCCompileOptions {..}) ->
               runCompileGHC (do
                 case targetGhc of
@@ -1935,6 +1942,7 @@ Report bugs at <https://gitlab.haskell.org/haskell/ghcup-hs/issues>|]
                             patchDir
                             addConfArgs
                             buildFlavour
+                            hadrian
                 GHCupInfo { _ghcupDownloads = dls } <- lift getGHCupInfo
                 let vi = getVersionInfo (_tvVersion targetVer) GHC dls
                 when setCompile $ void $ liftE $