Fix positionMapping in stale data

Author: soulomoon

ghcide/src/Development/IDE/Core/PositionMapping.hs

@@ -123,6 +123,10 @@ mkDelta cs = foldl' applyChange idDelta cs
 addDelta :: PositionDelta -> PositionMapping -> PositionMapping
 addDelta delta (PositionMapping pm) = PositionMapping (composeDelta delta pm)
 
+-- | Add a old delta onto a Mapping k n to make a Mapping (k - 1) n
+addOldDelta :: PositionDelta -> PositionMapping -> PositionMapping
+addOldDelta delta (PositionMapping pm) = PositionMapping (composeDelta pm delta )
+
 -- TODO: We currently ignore the right hand side (if there is only text), as
 -- that was what was done with lsp* 1.6 packages
 applyChange :: PositionDelta -> TextDocumentContentChangeEvent -> PositionDelta

ghcide/src/Development/IDE/Core/Shake.hs

@@ -443,7 +443,7 @@ lastValueIO s@ShakeExtras{positionMapping,persistentKeys,state} k file = do
                               `catch` (\(_ :: IOException) -> pure Nothing)
                 atomicallyNamed "lastValueIO 2" $ do
                   STM.focus (Focus.alter (alterValue $ Stale (Just del) actual_version (toDyn v))) (toKey k file) state
-                  Just . (v,) . addDelta del <$> mappingForVersion positionMapping file actual_version
+                  Just . (v,) . addOldDelta del <$> mappingForVersion positionMapping file actual_version
 
         -- We got a new stale value from the persistent rule, insert it in the map without affecting diagnostics
         alterValue new Nothing = Just (ValueWithDiagnostics new mempty) -- If it wasn't in the map, give it empty diagnostics
@@ -459,7 +459,7 @@ lastValueIO s@ShakeExtras{positionMapping,persistentKeys,state} k file = do
         Succeeded ver (fromDynamic -> Just v) ->
             atomicallyNamed "lastValueIO 5"  $ Just . (v,) <$> mappingForVersion positionMapping file ver
         Stale del ver (fromDynamic -> Just v) ->
-            atomicallyNamed "lastValueIO 6"  $ Just . (v,) . maybe id addDelta del <$> mappingForVersion positionMapping file ver
+            atomicallyNamed "lastValueIO 6"  $ Just . (v,) . maybe id addOldDelta del <$> mappingForVersion positionMapping file ver
         Failed p | not p -> readPersistent
         _ -> pure Nothing