Add support for the multi unit argument syntax introduced in GHC 9.4: https://downloads.haskell.org/ghc/9.4.4/docs/users_guide/using.html#multiple-home-units

We now support arguments of the form
```
-unit @unitA -unit @unitb
```

where the response files `unitA` and `unitB` contain the actual list of arguments for that unit:

```
-this-unit-id a-0.1.0.0
-i
-isrc
A1
A2
```

Also refactor the session loader and simplify it.

Also adds error messages on GHC 9.4 if the units are not closed (#3422).

fixes

Fix closure check

session-loader: override old units with new in multi-unit support

Author: wz1000

ghcide/ghcide.cabal

@@ -170,6 +170,7 @@ library
         Development.IDE.Core.UseStale
         Development.IDE.GHC.Compat
         Development.IDE.GHC.Compat.Core
+        Development.IDE.GHC.Compat.CmdLine
         Development.IDE.GHC.Compat.Env
         Development.IDE.GHC.Compat.Iface
         Development.IDE.GHC.Compat.Logger

ghcide/session-loader/Development/IDE/Session.hs

@@ -0,0 +1,48 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE RankNTypes #-}
+
+-- | Compat module Interface file relevant code.
+module Development.IDE.GHC.Compat.CmdLine (
+          processCmdLineP
+        , CmdLineP (..)
+        , getCmdLineState
+        , putCmdLineState
+        , Flag(..)
+        , OptKind(..)
+        , EwM
+        , defFlag
+        , liftEwM
+    ) where
+
+#if MIN_VERSION_ghc(9,3,0)
+import GHC.Driver.Session (processCmdLineP, CmdLineP (..), getCmdLineState, putCmdLineState)
+import GHC.Driver.CmdLine
+#else
+
+#if MIN_VERSION_ghc(9,0,0)
+import GHC.Driver.CmdLine
+#else
+import CmdLineParser
+#endif
+
+import Control.Monad.IO.Class
+import Control.Monad.Trans.State
+import GHC (Located, mkGeneralLocated)
+import GHC.ResponseFile
+import Control.Exception
+#endif
+
+#if !MIN_VERSION_ghc(9,3,0)
+-- | A helper to parse a set of flags from a list of command-line arguments, handling
+-- response files.
+processCmdLineP
+    :: forall s m. MonadIO m
+    => [Flag (CmdLineP s)]  -- ^ valid flags to match against
+    -> s                    -- ^ current state
+    -> [Located String]     -- ^ arguments to parse
+    -> m (([Located String], [Err], [Warn]), s)
+                            -- ^ (leftovers, errors, warnings)
+processCmdLineP activeFlags s0 args =
+    pure $ runCmdLine (processArgs activeFlags args) s0
+
+#endif

ghcide/src/Development/IDE/GHC/Compat/CmdLine.hs

@@ -51,6 +51,7 @@ module Development.IDE.GHC.Compat.Env (
     Backend,
     setBackend,
     Development.IDE.GHC.Compat.Env.platformDefaultBackend,
+    workingDirectory
     ) where
 
 import           GHC                                 (setInteractiveDynFlags)
@@ -110,6 +111,11 @@ hsc_EPS :: HscEnv -> UnitEnv
 hsc_EPS = hsc_unit_env
 #endif
 
+#if !MIN_VERSION_ghc(9,3,0)
+workingDirectory :: a -> Maybe b
+workingDirectory _ = Nothing
+#endif
+
 #if !MIN_VERSION_ghc(9,2,0)
 type UnitEnv = ()
 newtype Logger = Logger { log_action :: LogAction }

ghcide/src/Development/IDE/GHC/Compat/Env.hs

@@ -5,9 +5,7 @@
 module Development.IDE.GHC.Compat.Units (
     -- * UnitState
     UnitState,
-#if MIN_VERSION_ghc(9,3,0)
     initUnits,
-#endif
     oldInitUnits,
     unitState,
     getUnitName,
@@ -160,8 +158,12 @@ initUnits unitDflags env = do
         , ue_eps             = ue_eps (hsc_unit_env env)
         }
   pure $ hscSetFlags dflags1 $ hscSetUnitEnv unit_env env
+#else
+initUnits :: [DynFlags] -> HscEnv -> IO HscEnv
+initUnits _df env = pure env -- Can't do anything here, oldInitUnits should already be called
 #endif
 
+
 -- | oldInitUnits only needs to modify DynFlags for GHC <9.2
 -- For GHC >= 9.2, we need to set the hsc_unit_env also, that is
 -- done later by initUnits

ghcide/src/Development/IDE/GHC/Compat/Units.hs

@@ -0,0 +1,18 @@
+-this-package-name
+a
+-working-dir
+a
+-fbuilding-cabal-package
+-O0
+-i.
+-this-unit-id
+a-1.0.0-inplace
+-hide-all-packages
+-Wmissing-home-modules
+-no-user-package-db
+-package
+base
+-package
+text
+-XHaskell98
+A

ghcide/test/data/multi-unit/a-1.0.0-inplace

@@ -0,0 +1,3 @@
+module A(foo) where
+import Data.Text
+foo = ()

ghcide/test/data/multi-unit/a/A.hs

@@ -0,0 +1,19 @@
+-this-package-name
+b
+-working-dir
+b
+-fbuilding-cabal-package
+-O0
+-i
+-i.
+-this-unit-id
+b-1.0.0-inplace
+-hide-all-packages
+-Wmissing-home-modules
+-no-user-package-db
+-package-id
+a-1.0.0-inplace
+-package
+base
+-XHaskell98
+B

ghcide/test/data/multi-unit/b-1.0.0-inplace

@@ -0,0 +1,3 @@
+module B(module B) where
+import A
+qux = foo

ghcide/test/data/multi-unit/b/B.hs

@@ -0,0 +1,19 @@
+-this-package-name
+c
+-working-dir
+c
+-fbuilding-cabal-package
+-O0
+-i
+-i.
+-this-unit-id
+c-1.0.0-inplace
+-hide-all-packages
+-Wmissing-home-modules
+-no-user-package-db
+-package-id
+a-1.0.0-inplace
+-package
+base
+-XHaskell98
+C

ghcide/test/data/multi-unit/c-1.0.0-inplace

@@ -0,0 +1,3 @@
+module C(module C) where
+import A
+cux = foo

ghcide/test/data/multi-unit/c/C.hs

@@ -0,0 +1,2 @@
+packages: a b c
+multi-repl: True

ghcide/test/data/multi-unit/cabal.project

@@ -0,0 +1,6 @@
+cradle:
+  direct:
+    arguments: ["-unit" ,"@a-1.0.0-inplace"
+               ,"-unit" ,"@b-1.0.0-inplace" 
+               ,"-unit" ,"@c-1.0.0-inplace"
+               ]