Demote home unit closure errors to warnings.

Users can't really do anything to fix them until cabal 3.12 is released.
Perhaps they could previously get by despite the unsoundess before we started
throwing these errors.

So demote them to warnings to allow HLS to continue to "function" despite them.

Author: wz1000

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

@@ -817,71 +817,66 @@ newComponentCache recorder exts cradlePath _cfp hsc_env old_cis new_cis = do
           home_unit_id <- uids
           home_unit_env <- maybeToList $ unitEnv_lookup_maybe home_unit_id $ hsc_HUG hscEnv'
           map (home_unit_id,) (map (Compat.toUnitId . fst) $ explicitUnits $ homeUnitEnv_units home_unit_env)
-
-    case closure_errs of
-      errs@(_:_) -> do
-        let rendered_err = map (ideErrorWithSource (Just "cradle") (Just DiagnosticSeverity_Error) _cfp . T.pack . Compat.printWithoutUniques) errs
-            res = (rendered_err,Nothing)
-            dep_info = foldMap componentDependencyInfo (filter isBad $ Map.elems cis)
-            bad_units = OS.fromList $ concat $ do
-              x <- bagToList $ mapBag errMsgDiagnostic $ unionManyBags $ map Compat.getMessages errs
-              DriverHomePackagesNotClosed us <- pure x
-              pure us
-            isBad ci = (homeUnitId_ (componentDynFlags ci)) `OS.member` bad_units
-        return [([TargetDetails (TargetFile _cfp) res dep_info [_cfp]],(res,dep_info))]
-      [] -> do
+        multi_errs = map (ideErrorWithSource (Just "cradle") (Just DiagnosticSeverity_Warning) _cfp . T.pack . Compat.printWithoutUniques) closure_errs
+        dep_info = foldMap componentDependencyInfo (filter isBad $ Map.elems cis)
+        bad_units = OS.fromList $ concat $ do
+            x <- bagToList $ mapBag errMsgDiagnostic $ unionManyBags $ map Compat.getMessages closure_errs
+            DriverHomePackagesNotClosed us <- pure x
+            pure us
+        isBad ci = (homeUnitId_ (componentDynFlags ci)) `OS.member` bad_units
 #else
-    do
+    let isBad = const False
+        multi_errs = []
 #endif
-        -- Whenever we spin up a session on Linux, dynamically load libm.so.6
-        -- in. We need this in case the binary is statically linked, in which
-        -- case the interactive session will fail when trying to load
-        -- ghc-prim, which happens whenever Template Haskell is being
-        -- evaluated or haskell-language-server's eval plugin tries to run
-        -- some code. If the binary is dynamically linked, then this will have
-        -- no effect.
-        -- See https://github.com/haskell/haskell-language-server/issues/221
-        -- We need to do this after the call to setSessionDynFlags initialises
-        -- the loader
-        when (os == "linux") $ do
-          initObjLinker hscEnv'
-          res <- loadDLL hscEnv' "libm.so.6"
-          case res of
-            Nothing  -> pure ()
-            Just err -> logWith recorder Error $ LogDLLLoadError err
-
-        forM (Map.elems cis) $ \ci -> do
-          let df = componentDynFlags ci
-          let createHscEnvEq = maybe newHscEnvEqPreserveImportPaths newHscEnvEq cradlePath
-          thisEnv <- do
+    -- Whenever we spin up a session on Linux, dynamically load libm.so.6
+    -- in. We need this in case the binary is statically linked, in which
+    -- case the interactive session will fail when trying to load
+    -- ghc-prim, which happens whenever Template Haskell is being
+    -- evaluated or haskell-language-server's eval plugin tries to run
+    -- some code. If the binary is dynamically linked, then this will have
+    -- no effect.
+    -- See https://github.com/haskell/haskell-language-server/issues/221
+    -- We need to do this after the call to setSessionDynFlags initialises
+    -- the loader
+    when (os == "linux") $ do
+      initObjLinker hscEnv'
+      res <- loadDLL hscEnv' "libm.so.6"
+      case res of
+        Nothing  -> pure ()
+        Just err -> logWith recorder Error $ LogDLLLoadError err
+
+    forM (Map.elems cis) $ \ci -> do
+      let df = componentDynFlags ci
+      let createHscEnvEq = maybe newHscEnvEqPreserveImportPaths newHscEnvEq cradlePath
+      thisEnv <- do
 #if MIN_VERSION_ghc(9,3,0)
-                -- In GHC 9.4 we have multi component support, and we have initialised all the units
-                -- above.
-                -- We just need to set the current unit here
-                pure $ hscSetActiveUnitId (homeUnitId_ df) hscEnv'
+            -- In GHC 9.4 we have multi component support, and we have initialised all the units
+            -- above.
+            -- We just need to set the current unit here
+            pure $ hscSetActiveUnitId (homeUnitId_ df) hscEnv'
 #else
-                -- This initializes the units for GHC 9.2
-                -- Add the options for the current component to the HscEnv
-                -- We want to call `setSessionDynFlags` instead of `hscSetFlags`
-                -- because `setSessionDynFlags` also initializes the package database,
-                -- which we need for any changes to the package flags in the dynflags
-                -- to be visible.
-                -- See #2693
-                evalGhcEnv hscEnv' $ do
-                  _ <- setSessionDynFlags df
-                  getSession
+            -- This initializes the units for GHC 9.2
+            -- Add the options for the current component to the HscEnv
+            -- We want to call `setSessionDynFlags` instead of `hscSetFlags`
+            -- because `setSessionDynFlags` also initializes the package database,
+            -- which we need for any changes to the package flags in the dynflags
+            -- to be visible.
+            -- See #2693
+            evalGhcEnv hscEnv' $ do
+              _ <- setSessionDynFlags df
+              getSession
 #endif
-          henv <- createHscEnvEq thisEnv (zip uids dfs)
-          let targetEnv = ([], Just henv)
-              targetDepends = componentDependencyInfo ci
-              res = ( targetEnv, targetDepends)
-          logWith recorder Debug $ LogNewComponentCache res
-          evaluate $ liftRnf rwhnf $ componentTargets ci
+      henv <- createHscEnvEq thisEnv (zip uids dfs)
+      let targetEnv = (if isBad ci then multi_errs else [], Just henv)
+          targetDepends = componentDependencyInfo ci
+          res = ( targetEnv, targetDepends)
+      logWith recorder Debug $ LogNewComponentCache res
+      evaluate $ liftRnf rwhnf $ componentTargets ci
 
-          let mk t = fromTargetId (importPaths df) exts (targetId t) targetEnv targetDepends
-          ctargets <- concatMapM mk (componentTargets ci)
+      let mk t = fromTargetId (importPaths df) exts (targetId t) targetEnv targetDepends
+      ctargets <- concatMapM mk (componentTargets ci)
 
-          return (L.nubOrdOn targetTarget ctargets, res)
+      return (L.nubOrdOn targetTarget ctargets, res)
 
 {- Note [Avoiding bad interface files]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~