Populate ms_hs_date in GetModSummary rule

src/Development/IDE/Core/Compile.hs

@@ -84,6 +84,8 @@ import           System.IO.Extra
 import Control.DeepSeq (rnf)
 import Control.Exception (evaluate)
 import Exception (ExceptionMonad)
+import Data.Time (getCurrentTime)
+import System.IO.Error (isDoesNotExistError)
 import TcEnv (tcLookup)
 
 
@@ -451,6 +453,10 @@ getModSummaryFromImports
   -> Maybe SB.StringBuffer
   -> ExceptT [FileDiagnostic] m ModSummary
 getModSummaryFromImports fp contents = do
+    fileModTime <- liftIO $ getModificationTime fp `catch` \e ->
+        if isDoesNotExistError e
+            then getCurrentTime -- Virtual file case
+            else throwIO e
     (contents, dflags) <- preprocessor fp contents
     (srcImports, textualImports, L _ moduleName) <-
         ExceptT $ liftIO $ first (diagFromErrMsgs "parser" dflags) <$> GHC.getHeaderImports dflags contents fp fp
@@ -469,10 +475,7 @@ getModSummaryFromImports fp contents = do
 #if MIN_GHC_API_VERSION(8,8,0)
                 , ms_hie_date     = Nothing
 #endif
-                , ms_hs_date      = error "Rules should not depend on ms_hs_date"
-        -- When we are working with a virtual file we do not have a file date.
-        -- To avoid silent issues where something is not processed because the date
-        -- has not changed, we make sure that things blow up if they depend on the date.
+                , ms_hs_date      = fileModTime
                 , ms_hsc_src      = sourceType
                 -- The contents are used by the GetModSummary rule
                 , ms_hspp_buf     = Just contents