#12415: Fancy BinIface encoding for tuples is broken for constraint tuples -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #12357 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by bgamari: @@ -26,1 +26,2 @@ - to identify them for special handling during serialization. + to identify them for special handling during serialization, when we only + have the `Name` to look at. New description: We have a special way of encoding tuple-related names in the interface file symbol table. See `Note [Symbol table representation of names]`. However, it was broken for constraint tuples by ffc21506894c7887d3620423aaf86bc6113a1071. Namely, `putName` now panics when given a constraint tuple, {{{#!hs putTupleName_ :: BinHandle -> TyCon -> TupleSort -> Word32 -> IO () putTupleName_ bh tc tup_sort thing_tag = -- ASSERT(arity < 2^(30 :: Int)) put_ bh (0x80000000 .|. (sort_tag `shiftL` 28) .|. (thing_tag `shiftL` 26) .|. arity) where (sort_tag, arity) = case tup_sort of BoxedTuple -> (0, fromIntegral (tyConArity tc)) UnboxedTuple -> (1, fromIntegral (tyConArity tc `div` 2)) -- See Note [Unboxed tuple RuntimeRep vars] in TyCon ConstraintTuple -> pprPanic "putTupleName:ConstraintTuple" (ppr tc) }}} While this currently doesn't break anything, this is only because the clever encoding isn't used for constraint tuples. I believe the problem is very similar to the one which prevented us from encoding tuple type representations in #12357 (see ticket:12357#comment:31). By unwiring constraint tuples it becomes harder to identify them for special handling during serialization, when we only have the `Name` to look at. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12415#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler