-setSrcSpan loc thing_inside
- | isGoodSrcSpan loc = updLclEnv (\env -> env { tcl_loc = loc }) thing_inside
- | otherwise = thing_inside -- Don't overwrite useful info with useless
+setSrcSpan loc@(RealSrcSpan _) thing_inside
+ = updLclEnv (\env -> env { tcl_loc = loc }) thing_inside
+-- Don't overwrite useful info with useless:
+setSrcSpan (UnhelpfulSpan _) thing_inside = thing_inside