#15621: Error message involving type families points to wrong location -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler (Type | Version: 8.4.3 checker) | Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): In particular, applying this change on top of the previous commit (d4fa088350913233520ffa7163ef188a63666262) is enough to make the bug surface: {{{#!diff diff --git a/compiler/utils/UniqDFM.hs b/compiler/utils/UniqDFM.hs index 10e8aa9..3d4b1d6 100644 --- a/compiler/utils/UniqDFM.hs +++ b/compiler/utils/UniqDFM.hs @@ -147,8 +147,13 @@ addToUDFM (UDFM m i) k v = UDFM (M.insert (getKey $ getUnique k) (TaggedVal v i) m) (i + 1) addToUDFM_Directly :: UniqDFM elt -> Unique -> elt -> UniqDFM elt -addToUDFM_Directly (UDFM m i) u v = - UDFM (M.insert (getKey u) (TaggedVal v i) m) (i + 1) +addToUDFM_Directly (UDFM m i) u v + = UDFM (M.insertWith tf (getKey u) (TaggedVal v i) m) (i + 1) + where + tf (TaggedVal new_v _) (TaggedVal _ old_i) = TaggedVal new_v old_i + -- Keep the old tag, but insert the new value + -- This means that udfmToList typically returns elements + -- in the order of insertion, rather than the reverse addToUDFM_Directly_C :: (elt -> elt -> elt) -> UniqDFM elt -> Unique -> elt -> UniqDFM elt }}} Since that comment mentions that `udfmToList` now returns elements in a different order than it did previously, I wonder if there is some code which was sensitive to `udfmToList`'s order that wasn't updated properly... -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15621#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler