Cabal uses main as the unit id of all executable packages. This confused multi component sessions.

Solution: include the hash of the options in the unit id when the unit id is called "main".

Fixes #3513

Author: wz1000

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

@@ -484,7 +484,22 @@ loadSessionWithOptions recorder SessionLoadingOptions{..} dir = do
         packageSetup (hieYaml, cfp, opts, libDir) = do
           -- Parse DynFlags for the newly discovered component
           hscEnv <- emptyHscEnv ideNc libDir
-          (df, targets) <- evalGhcEnv hscEnv $ setOptions opts (hsc_dflags hscEnv)
+          (df', targets) <- evalGhcEnv hscEnv $ setOptions opts (hsc_dflags hscEnv)
+          let df =
+#if MIN_VERSION_ghc(9,3,0)
+                case unitIdString (homeUnitId_ df) of
+                     -- cabal uses main for the unit id of all executable packages
+                     -- This makes multi-component sessions confused about what
+                     -- options to use for that component.
+                     -- Solution: hash the options and use that
+                     "main" ->
+                       let hash = B.unpack $ B16.encode $ H.finalize $ H.updates H.init (map B.pack $ componentOptions opts)
+                           hashed_uid = Compat.toUnitId (Compat.stringToUnit ("main-"++hash))
+                       in setHomeUnitId_ hashed_uid df'
+#else
+                df'
+#endif
+
           let deps = componentDependencies opts ++ maybeToList hieYaml
           dep_info <- getDependencyInfo deps
           -- Now lookup to see whether we are combining with an existing HscEnv
@@ -499,6 +514,7 @@ loadSessionWithOptions recorder SessionLoadingOptions{..} dir = do
                   -- We will modify the unitId and DynFlags used for
                   -- compilation but these are the true source of
                   -- information.
+                  
                   new_deps = RawComponentInfo (homeUnitId_ df) df targets cfp opts dep_info
                                 : maybe [] snd oldDeps
                   -- Get all the unit-ids for things in this component