Revert back to GhcSession rule

Depending on GhcSessionDeps means we do not need to reload all the module
dependencies in the GHC session. On the other hand, with the GhcSession
dependency we *do* have to reload them (from interface files, hopefully)

Unfortunately, the ModSummary objects that GhcSessionDeps puts in the GHC
session are not suitable for reuse since they clear out the timestamps to avoid
internal bugs. This can probably be relaxed so that plugins like Eval can reuse
them.

Author: pepeiborra

src/Ide/Plugin/Eval.hs

@@ -36,7 +36,7 @@ import qualified Data.Text                      as T
 import           Data.Time                      (getCurrentTime)
 import           Development.IDE.Core.Rules     (runAction)
 import           Development.IDE.Core.RuleTypes (GetModSummary (..),
-                                                 GhcSessionDeps (..))
+                                                 GhcSession (..))
 import           Development.IDE.Core.Shake     (use_)
 import           Development.IDE.GHC.Util       (evalGhcEnv, hscEnv,
                                                  textToStringBuffer)
@@ -169,10 +169,22 @@ runEvalCmd lsp state EvalParams {..} = response' $ do
   contents <- liftIO $ getVirtualFileFunc lsp $ toNormalizedUri _uri
   text <- handleMaybe "contents" $ virtualFileText <$> contents
 
+{- Note: GhcSessionDeps
+
+Depending on GhcSession means we do need to reload all the module
+dependencies in the GHC session(from interface files, hopefully).
+
+The GhcSessionDeps dependency would allow us to reuse a GHC session preloaded
+with all the dependencies. Unfortunately, the ModSummary objects that
+GhcSessionDeps puts in the GHC session are not suitable for reuse since they
+clear out the timestamps; this is done to avoid internal ghcide bugs and
+can probably be relaxed so that plugins like Eval can reuse them. Once that's
+done, we want to switch back to GhcSessionDeps
+ -}
   session <-
     liftIO $
       runAction "runEvalCmd.ghcSession" state $
-        use_ GhcSessionDeps $
+        use_ GhcSession $ -- See the note on GhcSessionDeps
           toNormalizedFilePath' $
             fp