hls-notes-plugin: Improve "Note not found" error message

Author: jvanbruegge

plugins/hls-notes-plugin/src/Ide/Plugin/Notes.hs

@@ -87,7 +87,7 @@ jumpToNote state _ param
         note <- err "No note at this position" $ listToMaybe $
             mapMaybe (atPos $ fromIntegral c) $ matchAllText noteRefRegex line
         notes <- runActionE "notes.definedNotes" state $ useE MkGetNotes nfp
-        (noteFp, pos) <- err "Note not found" (HM.lookup note notes)
+        (noteFp, pos) <- err ("Note definition (a comment of the form `{- Note [" <> note <> "]\\n~~~ ... -}`") (HM.lookup note notes)
         pure $ InL (Definition (InL
                 (Location (fromNormalizedUri $ normalizedFilePathToUri noteFp) (Range pos pos))
             ))